Aerosols, Clouds, and Trace gases Research Infrastructure Network

Project Information

ACTRIS

Grant agreement ID: 262254

Project closed

Start date 1 April 2011

End date 31 March 2015

Funded under

• Specific Programme "Capacities": Research infrastructures

Total cost € 11 598 422,20

EU contribution € 7 800 000,00

Coordinated by

CONSIGLIO NAZIONALE DELLE RICERCHE
Italy

Final Report Summary - ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network)

Executive Summary:
Strengthening the ground-based component of the Earth Observing System for key atmospheric variables has been unambiguously asserted in the IPCC Fourth Assessment Report and the EU Thematic Strategy on air pollution. Key climate variables not only concern CO2 and other greenhouse gases but also the short-lived components driving the interaction between solar radiation and the atmosphere, aerosols and clouds. Their radiative impact and the understanding of their evolution in gas-aerosolcloud- interactions constitute the main uncertainty in predicting future air quality and climate change.
The ACTRIS “Aerosols, Clouds, and Trace gases Research InfraStructure Network” project is an European Commission FP-7-Project aiming at integrating European ground-based stations equipped with advanced atmospheric probing instrumentation for aerosols, clouds, and short-lived gas-phase species. The project is coordinated by CNR (Italy) and CNRS (France) and has 29 partners. ACTRIS consortium represents 35 infrastructures in 24 European countries; furthermore, more than 60 sites are reporting ACTRIS labeled data.
The ACTRIS project is an essential pillar of the EU ground-based observing system that provides the long-term observations information required to understand current variability of the atmospheric aerosol components and better predict their impact on climate and air quality in a changing climate. ACTRIS provides the key information required to develop the proper level of understanding on the evolution of the aerosol cycle, including attribution of sources and sinks, assessment of climate forcing and possible climate feedbacks.
ACTRIS is developed in support of the EU research initiatives and designed and operated as an essential support of operational networks for long-term air quality monitoring and of the on-going development of atmospheric services within GMES/COPERNICUS. ACTRIS is supporting and complementing aircraft and satellite observations and has the important role in validation, integration, full exploitation of remote sensing data. The ACTRIS infrastructure deliver critical long-term datasets for the climate and air quality research including evaluation of weather forecast and climate models. ACTRIS is also linked to the main international coalition of Earth observations, the GEOSS, Global Earth Observation System of Systems. ACTIS data products are related to nearly all societal benefit areas of GEOSS: disasters, health, climate, water, weather, ecosystems, agriculture and biodiversity.
The strategic focus of ACTRIS is to ensure the long-term continuation of advanced measurements on aerosols, clouds and reactive gases in Europe in a coordinated and cost-efficient way. Thus the ACTRIS framework is focused to be part of the European Union research infrastructure landscape ensuring Europe’s competitiveness in “frontier” research.

Project Context and Objectives:
Climate change is for a large part governed by atmospheric processes, in particular the interaction between radiation and atmospheric components (e.g. aerosols, clouds, greenhouse and trace gases). Some of these components are also those with adverse health effects influencing air quality. Strengthening the ground-based component of the Earth Observing System for these key atmospheric variables has unambiguously been asserted in the IPCC Fourth Assessment Report and Thematic Strategy on air pollution of the EU. ACTRIS (Aerosols, Clouds and Trace gases Research InfraStructure Network) aims to coordinate the European ground-based network of stations equipped with advanced atmospheric probing instrumentation for aerosols, clouds and short-lived trace gases by integrating three existing research infrastructures EUSAAR, EARLINET, CLOUDNET, and a new trace gas network component into a single coordinated framework.
The main objectives of ACTRIS are:
• To provide long-term observational data relevant to climate and air quality research on the regional scale produced with standardized or comparable procedures throughout the network and to substantially increase the number of high-quality data accessible through the ACTRIS data centre.
• To provide a coordinated framework to support trans-national access to large infrastructures, strengthening high-quality collaboration in and outside the EU and access to high-quality information and services for the user communities and increasing the use of European advanced infrastructures for atmospheric research.
• To develop new integration tools to fully exploit the use of multiple atmospheric techniques at ground-based stations, in particular for the calibration/validation/integration of satellite sensors and for the improvement of global and regional scale climate and air quality models.
• To enhance training of new users in particular students, young scientists, and scientists from eastern European and non-EU developing countries in the field of atmospheric observation to become future leaders in the field and to promote scientific excellence in less-favoured regions in Europe.
• To promote the development of new technologies for atmospheric observation of aerosols, clouds and trace gases through close partnership with European SMEs.
ACTRIS establishes an operational network for long-term atmospheric observations makes an essential contribution for building the scientific knowledge required to support policy issues on air quality and climate change in Europe.

A key for ACTRIS success is that it is built on the basis of a consortium joining existing networks/observatories that were already providing consistent datasets of observations performed using state-of-the-art measurement technology and data processing. In particular the ACTRIS consortium merges two existing research infrastructures funded by the European Commission under FP6: EUSAAR (European Supersites for Atmospheric Aerosol Research) and EARLINET (European Aerosol Research Lidar Network). ACTRIS also includes the distributed infrastructure on aerosol – cloud interaction existing from a previous EU Research project CLOUDNET and by grouping the existing EU ground-based monitoring capacity for short-lived trace gases which is, at present, not coordinated at any level, besides EMEP (European Monitoring and Evaluation Programme) and GAW (Global Atmosphere Watch) caring for a few specific compounds. Therefore, ACTRIS represents an unprecedented effort towards integration of a distributed network of ground-based stations, covering most climatic regions of Europe, and responding to a strong demand from the atmospheric research community. ACTRIS represents a step towards better integration of aerosol, cloud and trace gases communities in Europe necessary to match the integration of high-quality long-term observations of aerosol, clouds and short-lived gas-phase species and for assessing their impact on climate and environment. ACTRIS outcomes will be used for supporting decisions in a wide range of policy areas, including air quality but also health, international protocols and research requirements.

ACTRIS is organized in Networking Activities, Transnational Access and Service Activities, and Joint Research Activities.

The data provision structure in ACTRIS involves four networking activities (NAs) that feed the data centre:
WP2: Remote sensing of vertical aerosol distribution
WP3: In-situ chemical, physical and optical properties of aerosols
WP4: Trace gases networking: Volatile organic carbon and nitrogen oxides
WP5: Clouds and aerosol quality-controlled observations
These networking activities are completed by a fifth networking activity aimed at integrating information from WP2-5 into a higher level of products required by users in the modelling and satellite-validation communities: WP6: Integration, outreach, and sustainability.

The activities of the research infrastructure have been oriented to a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardized data exchange format. ACTRIS has also strongly sustained effective partnership between users and data providers and pursued innovative initiatives to address the need of users. Moreover, standardization of procedures for the different measurement techniques and best practices across all stations and all European climatic regimes have been paramount to facilitate the coordinated expansion of the network in a sustainable and efficient way.

Transnational access activities and service activities enable users to conduct high-quality research by:
- Offering access to infrastructures with an excellent combination of instruments and expertise. This gives the opportunity to perform experiments using the state-of-art equipment in atmospheric research which could be used for measurement campaigns or instrument tests (WP7-17: Trans-National Access).
- Training a new generation of scientists. ACTRIS activities have been aimed at enhancing the accessibility to the observatories and the exploitation of technical resources and knowledge. This is organized through WP6 and WP7-17.
- Offering to the whole scientific community the use of a unique sun photometer calibration facility currently operational in the frame of PHOTONS/AERONET. This is performed in WP18: AERONET-EUROPE Calibration Service.
- Enhancing access to information on advanced aerosols, clouds and trace gases high-quality data in Europe through a Service Activity (WP19: The ACTRIS Service Centre: Access to observations and service products of the infrastructure). The data centre integrates measurement data from the ACTRIS infrastructure and other highly relevant networks. In addition to free access to atmospheric high-quality data, the data centre provides tools and applications for end users to facilitate the use of all measurements for broad user communities, offer a direct interface towards external users (e.g. MACC, GMES in-situ), and take into account the principles outlined in SEIS, INSPIRE, WIS and GEOSS.

Joint research activities have been conducted to support and promote the ACTRIS infrastructure by taking advantage of the synergistic effects of coordinating different observation capabilities. WP20 and WP22 address novel techniques and algorithms using a multi-sensor approach to improve observation performances and define new data products. WP21 focuses on investigating technological and methodological aspects of simultaneously networking real-time chemical composition of aerosols and trace gases. These JRAs are topically connected with networking activities and in cooperation with WP6 to ensure their results are assimilated for the whole ACTRIS infrastructure benefit.
At international level ACTRIS has operated in strong cooperation with the Global Atmospheric Watch Program of the WMO, the ARM Climate Research Program and all the relevant research networks as (i.e. AERONET, GALION, NDACC, etc.) for the establishment of the ground-based component of the Global Earth Observation System of Systems.
Many efforts were made to establish to conditions for long-term sustainability of the Research Infrastructure by developing the National ACTRIS framework supporting the ACTRIS application to the European ESFRI roadmap, submitted in March 2015 with official support of 21 countries.

Project Results:
Over the 4 years of activity, ACTRIS achieved the expected work programme, mainly aimed at consolidating the actions initiated in EUSAAR, EARLINET, and CLOUDNET on one side (WP2,WP3 and WP5), developing the Trace Gases component (WP4) and ensuring integration of these communities (WP6 and JRAs), its long-term sustainability and its visibility in the International observation system on the other side. It is clearly the case that ACTRIS is now recognized as a key player of the observing system, for its role in data provision to the scientific community but also for its action in observing metrology for aerosol, cloud, and trace gases. During the 4 years, ACTRIS developed the expected level of service recognized by an increasing number of users in different scientific communities.

WP2, implemented as a networking action addressing remote sensing of vertical aerosol distribution, i.e. the aerosol lidar component of the infrastructure, was organized in three main tasks:
- Task 2.1: Exchange of expertise
- Task 2.2: Quality assurance
- Task 2.3: Improvement of lidar techniques and data analysis for aerosol characterization.

Task 2.1 was the instrument to spread methods, good practices and knowledge generated in the work package and other work packages, as well as to achieve integration within the whole infrastructure and to provide outreach with the scientific community at large.
The achievements can be classified in terms of methodology, observations and integration and outreach.
1. Methodological achievements.
WP2 has enabled a well-defined and rigorous quality-assurance program for the instruments to guarantee the quality of lidar data. The program consists of two parts:
a) Direct intercomparison of instruments against standard systems. Ideally all the lidars in the infrastructure should by default be periodically (every few years) compared to a standard looking at the same atmosphere, either by moving the system, if it is possible, to the standard location or a standard (standard are transportable) to the location of the system to be tested. Priority is given to the intercomparison of new systems or those having undergone major upgrades. During the project span three such intercomparisons (L’Aquila system against Munich POLIS standard, Naples and Lecce systems against Potenza standard MUSA) have been carried out. In addition, technical support has been provided to new systems (Cork and Clermont-Ferrand).
b) Internal hardware checkups. A battery of tests to be performed by every station to check some aspects of the operation (alignment, interferences, synchronism, ratio between instrument constants in channels used for depolarization measurements…) has been defined. The tests must be performed and reported either at least once a year or whenever the system has undergone a major change, depending on the type of test. These tests have been fully documented in deliverable D2.12 and are ready to be included in the Single Calculus Chain (SCC) for lidar data processing.
Combing efforts carried out in tasks 2.2 and 2.3 a new quality assured product, the linear particle depolarization ratio, has been added to the set of aerosol profiling products and included into the SCC. Detailed procedures for calibrated depolarization measurement, including uncertainty estimation, are reported in deliverable D2.7
Methods have also been developed to automatically detect aerosol layers and determine their geometrical and optical properties. These are documented in deliverable D2.10.
The organization of task 2.1 workshops jointly with WP20 (JRA1: Lidar and sunphotometer – Improved instruments, integrated observations and combined algorithms) has resulted in a very effective dissemination among the ACTRIS lidar community of the methods developed in this joint research action, in particular regarding the lidar and sunphotometer combined algorithms. Many groups not formally involved in WP20 are using them and providing feedback for their improvement.
During the ACTRIS project the EARLINET database of lidar products has been integrated into the ACTRIS Data Center and it has expanded since ACTRIS start by nearly 17000 quality-assured datasets distributed into different categories: climatology, which is the essential and most populated one, plus others comprising special elements, events or observations (cirrus, stratosphere, Saharan dust outbreaks, volcanic eruptions, forest fires, photochemical smog, rural/urban aerosol, diurnal cycles, correlative measurements with CALIPSO overpasses).
Also two new lidar station (Clermont-Ferrand and Lille) have become active into the infrastructure, bringing the count of active stations to 29.
The web graphic interface to the SCC allows to decrease the time between measurement and public availability of data products by increasing the throughput of the product-generation process.

Integration (both within WP2 and across work packages) and outreach has been obtained in several ways:
- Contribution to campaigns.
EMEP/PEGASOS intensive observation period (IOP) between 8 June and 17 July 2012, to which ACTRIS WP2 contributed along with WP3 and WP4. In this IOP all the WP2 stations contributed with their regular climatology measurements and additional measurements associated to special events, such as forest fires and Saharan dust outbreaks. Moreover, 10 stations provided daily lidar-profiling measurements around sunset for the whole 8 June – 17 July 2012 period.
ChArMEx IOP from 25 June to 12 July 2012: within this campaign a demonstration was carried out of the capability of a coordinated set of many advanced aerosol lidar stations (10 in this case) spread over a wide geographical area (the Mediterranean basin in this case) to function as an operational network. This exercise involved the capability of the SCC to provide near real time products from data from many stations that can be assimilated into air-quality models.
ChArMEx/ADRIMED joint field campaign, between 10 June and 15 July 2013, aimed at the characterization of the typical “Mediterranean aerosol” and its direct radiative forcing (column closure and regional scale).
- Exchange of expertise with the aerosol lidar community outside ACTRIS.
One WP2-WP20 workshop (Lille, France, 28-31 October 2014) was especially devoted to exchanges with experts of WMO’s GAW Aerosol Lidar Observation Network (GALION). Twelve experts attended, with special representation (eight experts) of the Latin America Aerosol Lidar Network (LALINET).
- Publication and dissemination activites.
ACTRIS WP2 activities have resulted in numerous publications in peer-reviewed journals with high impact factor, reported in the publications list. It has also been present in the main conferences dealing with lidar aerosol remote sensing. In particular the 26th International Laser Radar Conference (Porto Heli, Greece, 25-29 June 2012) was organized by members of the National Technical University of Athens, the Aristotle University of Thessaloniki, and the National Observatory of Athens, active in ACTRIS WP2. ACTRIS WP2 contributed to more than 5% of the around 275 presentation in the conference. ACTRIS WP2 has also been present in the EGU annual meetings, having a special session devoted to EARLINET in the 2015 edition.
Regarding publications in peer-reviewed journals, a special issue devoted to EARLINET is underway in EGU’s Atmospheric Measurement Techniques journal, with some papers already published, where many of the results obtained in ACTRIS WP2 are or will be published.


In WP3 for the in-situ chemical, physical and optical properties of aerosols, the harmonization of mobility particle size spectrometer measurements to obtain of number size distribution measurements of submicrometer particles (particles larger than 10 nm) have been started in EUSAAR, leading to a recommendation article in 2012. This article has achieved a broad impact on the scientific and stakeholder community and is presently cited more than 100-times. These recommendations have been presently implemented 40 stations in Europe, performing particle number size distribution measurements. Since most of these instruments have in participating in the quality assurance program of ACTRIS central (intercomparison workshops or on-site intercomparisons), we can assume comparable data sets with known uncertainties for the entire ACTRIS network. The recommendations are also partly adopted for commercial instruments from SMEs. CEN/TC 264/WG 32 decided on the standardization for measurements of particle number concentration presently and works a draft for particle number size distribution measurements using mobility particle size spectrometer. The ACTRIS recommendations for particle number size distribution measurements are the base for the coming up CEN standardization.
Measurements of ion-cluster and Nanoparticles, especially smaller than 20nm in diameter have been related to high uncertainties in the beginning of ACTRIS. During ACTRIS, the standardization of Nano-mobility particle size spectrometers and ion spectrometer measurements (2-20nm) have been significantly improved and a measurement protocol is been developed for reliable aerosol particle number size distribution from 3 nm on. Ion cluster spectrometers are continuously used under standardized conditions at 6 European measurement sites within ACTRIS networks in parallel with mobility particle size spectrometers.
Quality assurances of particle light absorption photometers and Nephelometers (to obtain the particle light scattering coefficient) has started during the EUSAAR project. Correction methods for new types of Nephelometers have been developed, and furthermore knowledge was transferred to SMEs. Results of these activities have been published in three articles. Operating procedures and data protocols for particle absorption photometers and Nephelometers have been implemented. The existing protocols led to a high data quality during ACTRIS. A simplified correction formula was agreed on to transfer Aethalometer measurements to particle light absorption coefficients with an uncertainty of approximately 25%. Instruments specific differences of particle light absorption photometers stipulated the setup of a multi-wavelength reference method at the Leibniz Institute for Tropospheric research. The setup was planned to operate with ambient aerosol and to simulate ambient aerosols in the laboratory. The capability to measure absorption at multiple wavelengths was implemented to account for the growing interest in spectral absorption to detect organic aerosol. Protocols for calibrating multi wavelength absorption photometers are not yet developed.
Harmonized sampling and analysis of organic and elemental carbon was successfully implemented during the course of the ACTRIS project. During ACTRIS, the number of sites where organic and elemental carbon are regularly measured increased from 14 (12 partners + 2 associates) to 19 (15 partners + 4 associates). The sampling apparatus developed within EUSAAR to mitigate sampling artifacts has been implemented at 4 more sites (8 vs. 4), and the analytical protocol EUSAAR-2 is currently used by 7 more ACTRIS laboratories (17 vs. 10). The implementation of harmonized sampling and analytical methods considerably decreases the measurements’ uncertainties.
A good grip on data quality was obtained by running annual inter-laboratory comparisons for the measurement of total carbon (organic and elemental carbon) and elemental carbon. These exercises involved up to 16 participants (vs. 11 during the previous EUSAAR project), among which 6 are laboratories responsible for the analyses of organic and elemental carbon at the EMEP stations of their countries, and not partners in ACTRIS. Based on statistical techniques, we have determined the precision of the analytical method, and the performances of the participants.
We also made sustained efforts to get the technical results of ACTRIS disseminated beyond the project frame. The analytical protocol EUSAAR-2 was first adopted as the standard method by EMEP (Feb. 2014). The ad hoc working group of the Centre for European Normalization (CEN), who got the mandate from the European Commission to develop a European standard for the measurement of organic and elemental carbon in PM2.5 also chose EUSAAR-2 as the future standard protocol (March 2015). The development of a European standard for the measurement of organic and elemental carbon in PM2.5 will foster the implementation of the Directive 2008/50/EC which requires the chemical speciation of PM2.5 (incl. organic and elemental carbon) a rural background sites. It could also encourage European SMEs to develop and commercialize analytical instruments specifically conceived according to this new standard.
At the onset of ACTRIS, there was a definite lack of coordination regarding the methods for quantifying the atmospheric concentrations of relevant organic tracers. Quality-assured and intercomparable measurements of organic aerosol tracers are absolutely essential in order to be able to perform reliable OA source apportionment across Europe. This, in turn, is a prerequisite for measures taken to mitigate the PM population exposure, aimed at cost-efficient reduction of human health effects.
Within the ACTRIS time frame, considerable progress was made towards the establishment of standard operating procedures for major source categories, and to implement them at a wide variety of sites across Europe. Draft standard operating procedures for analysis of tracers for biomass burning have been published and are openly accessible on the ACTRIS web pages. These standard operating procedures, as well as other for other candidate organic aerosol tracers, were widely implemented on a voluntary basis at several European sites in coordination with various national and EU research projects. Work still remains to establish standard operating procedures for more source categories, and also for secondary organic aerosols. These standard operating procedures also need to be acknowledged by the larger air quality community, such as EMEP.
WP3 also involved the development of standardized protocols measurement protocols for size- and supersaturation-resolved cloud condensation nuclei measurements. Continuous or intermittent cloud condensation nuclei measurements, triggered by the EUCAARI project, were already available at some ACTRIS stations, by the start of the ACTRIS project. However, resulting data sets were neither homogeneous nor readily accessible for potential users due to a lack of a common standardized operation procedure. One task was the development of a standard operation procedure for calibration and routinely operation of counters for cloud condensation nuclei. This was successfully achieved including the implementation of data formats for reporting different levels cloud condensation nuclei data to the data center. The ACTRIS project has triggered the installation of additional instruments and enabled the exchange between experts and know-how transfer to new or less experienced users. By the end of the ACTRIS project, cloud condensation nuclei counters are permanently operated at 8 stations and comparable and quality assured data sets are available in EBAS. Other users such as the BACCHUS project already started using these data sets with the goal to achieve a better understanding of the anthropogenic influence on cloud properties. A key element here is that complementary data sets of particle number size distribution and composition are available at the ACTRIS stations, which is necessary to understand the sources and processes leading to formation of cloud condensation nuclei. In particular the composition measurements have been newly implemented within ACTRIS. This reflects how ACTRIS has improved the scientific value of the aerosol monitoring efforts for scientific users.


WP4 was devoted to the trace gases component of ACTRIS: Volatile organic carbon (VOC) and nitrogen oxides (NOx).

ACTRIS WP4-VOC achieved:
- harmonization and standardization of European VOC measurement by improved QA/QC, data evaluation and reporting
- an overview article on inter-laboratory comparability and VOC measurement quality in Europe
- development of controlled final data with uncertainty and metadata-information in EBAS
- growing VOC infrastructure in Europe and users

Within ACTRIS, VOC measurements at representative European measurement sites have progressed in many different aspects. Continuous measurements performed in EMEP (European Monitoring and Evaluation Programme) and GAW were the focus of the activities. For these on-going measurement programmes only a basic assessment of the quality of the submitted data by station providers has been performed. Within ACTRIS this was improved in two ways. First, new data quality objectives (DQOs) were defined, which progressed from the existing DQOs of WMO (World Meteorological Organization). These DQOs were tested within a pan-European round-robin exercise (see below). Furthermore, together with the ACTRIS Data Centre meta data was reformulated and homogenized for submission to EBAS. Second, each measurement is newly accompanied with information on its quality (i.e. expanded uncertainty, precision), which have been commonly discussed at 4 workshops during the ACTRIS project. Before final submission data is now re-evaluated, making use of a newly developed on-line tool which allows the comparison of data quality between different European measurement sites. This is a major step forward to a RI and brings the European measurement stations in a world-leading position.
The state of the European VOC measurements was checked with a huge round-robin exercise comprising 25 instruments (GC-FID/GC-MS/PTR-MS) at 22 measurement sites. This is the largest VOC intercomparison world-wide for nearly a decade. Results of this exercise were essential for checking the abilities of European laboratories to reach the new DQOs of ACTRIS. Results were extremely encouraging for GC-FIDs and the long-lived alkanes. For GC-MS calibration with whole air standards was found to be challenging and the intercomparison provided the incentive for laboratories to change their calibration procedure. Several short-comings were detected and fixed at continuous measurement sites, such as peak overlaps, degraded separation columns, incomplete trapping of very volatile compounds. In essence, ACTRIS provided the framework which allowed the community to check the quality and comparability of the Pan-European VOC data submitted under EMEP and continuous research activities. Additionally, this effort was reinforced by VOC-audits at selected ACTRIS sites by the WCC-VOC (KIT).
Furthermore, oxidised VOCs (OVOCs) were the subject of a specific side-by-side intercomparison at Hohenpeissenberg (Germany) in 2013. Here different instruments for these very challenging measurements were compared. This allows the further development of measurement strategies for OVOCs and their inclusion into the European network for example under a future RI.
Within NA4 also the potential of linking in-situ and remote sensing information was explored at the high-Alpine site of Jungfraujoch (JFJ). At ground level the site was predominantly influenced by European and North American emissions. While Asian emissions become more important for the mid troposphere. Therefore, an in-situ correction scheme was devised to assess the extent to which in-situ information propagates into the upper troposphere, which was tested using C2H6 data at JFJ.

ACTRIS WP4-NOx achieved:
- a survey of inter-laboratory comparability and measurement quality
- harmonization and standardization of measurement procedures, QA/QC, data evaluation and reporting
- progress towards quality controlled final data with uncertainty and metadata-information in EBAS
- growing NOx infrastructure community in Europe

During ACTRIS, a round robin intercomparison of NO and a side-by-side intercomparison of NO and NO2 were performed to assess and evaluate the quality of calibration gases in use in the European RI ACTRIS and the ability of laboratories to correctly determine ambient mixing ratios of NO and NO2. The NO round robin intercomparison mostly showed results in line with the data quality objective (DQO) by ACTRIS and GAW for NO measurements of 3% and demonstrated the calibration intercomparability. The side-by-side intercomparison brought together state-of-the-art commercial NOx instruments and research instruments for direct NO2 determination by optical methods. While for synthetic test mixtures results were mostly in line with the ACTRIS-DQO’s, only best performing instruments were appropriate in ambient air, especially for NO2. NO2 measurements by molybdenum converters failed in achieving data within the DQO’s. Thus, good results are possible with commercial instruments but need comprehensive QA/QC.
Results of the comparisons together with the joint ACTRIS expert knowledge enabled the formulation of the first available, standardized NOx measurement guidelines, first as draft to support the ACTRIS measurement in periods 1-3, then at the end of ACTRIS as finals SOP’s. These summarize the state-of-the-art recommendations for long-term NOx measurements and are the basis for GAW MG. They contain standard instrumentation and maintenance, sampling, artefact description and correction, QA and QC including standard and zero gas measurement, uncertainty determination and data reporting procedures to EBAS including the necessary metadata, uncertainty, precision, and flag information. Only data submissions complying with these rules have been decided to be labelled as ACTRIS data in EBAS.
The WCC-NOx (FZ-Juelich) developed an audit procedure and performed its first audit. WCC-NOx also developed procedures for standardized annual station data evaluations. Data and station performances were discussed during meetings and action items were given back to the stations in order to improve their data. It is essential to hold such data workshop every year to ensure, further develop, and sustain the high ACTRIS data and quality standards.
In four workshops, in campaigns, during numerous telephone conferences and through bi- and multilateral co-operations the European NOx infrastructure has greatly improved during ACTRIS.
The potential of linking in-situ and remote sensing information with regard to NO2 was explored at Hohenpeissenberg Observatory (HBP) by means of a MAxDOAS instrument. The results look very promising. The MAxDOAS technique seems to be able to give additional information on NOx profile and serves as a linkage between ground based and satellite based observations. This technique will become operational in the next few years.


In WP5 the activity was focused on extending the Cloudnet infrastructure to provide continuous high resolution observations of vertical profiles of cloud and aerosol properties observed with ground-based vertically-pointing radar and lidar, i) at more locations over Europe, ii) for more variables, iii) with quantified errors and iv) with improved metrics to evaluate forecast and climate models. These observed profiles were compared with their representation in seven operational weather forecast models run by five European Weather Services. The first step was to classify the targets as clouds (liquid/ice), aerosols, or clear air etc, then to derive the variables held in the models, such as cloud fraction and cloud water content (ice and liquid) and a measure of aerosol loading which, in some models, is subdivided into different aerosol types. These variables were then mapped on to the grids used by the various models, typically 2-25 km in the horizontal and 40-137 vertical levels for weather forecast models. Statistics on the performance of the forecast models can then be derived each month to identify the shortcomings of the models; when upgraded versions of the models are introduced any improvements in the model representation of clouds and aerosols can be rapidly quantified. The forecast model converts the cloud water into precipitation, so faithful representation of clouds is therefore a pre-requisite for accurate forecasts of precipitation and flash-floods, similarly, accurate representation of aerosol is needed for predicting episodes of high pollution with consequent health risks. Uncertainty in how to represent clouds in climate models has been identified as the major cause of the present unacceptable spread in the predictions of future global warming; climate models use essentially the same parameterisation schemes as weather forecasts models, so improving weather forecast models will give us increased confidence in the predictions of climate models
The Cloudnet infrastructure provides continuous profiles of clouds and aerosols using the backscatter signals from ground-based vertically-pointing lidars and radars and has the following advantages over satellite observations in evaluating cloud and aerosol representation in models:
a) Only two satellites in low earth-orbit , CloudSat and Calispso currently have active radar and lidar providing vertical profiles of aerosols and clouds, but the narrow swath (about 1km) leads to very sparse sampling, long revisit times, at the same time of day, so any diurnal cycle in clouds and aersosol properties cannot be resolved.
b) CloudSat and Calipso will shortly be replaced by the EarthCARE satellite, but it will have the same narrow swath and sun-sychronous orbit. There are currently no future satellites planned with cloud/aerosol profiling capability.
c) The ’Cloudnet’ ground based instruments within ACTRIS can provide cloud and aerosol profiles with a vertical resolution of 30/60m every 30 seconds rather than 500 m resolution from the occasional visits by the satellite.
The following improvements to the Cloudnet infrastructure have been made during ACTRIS:
Task 5.1: An increase in the number of Cloudnet stations from the original four at Chilboton (UK), Cabauw (NL), Palaiseau (F), and Lindenberg (D), to nine by the addition of five extra stations at Juelich (D), Leipzig (D) Mace Head (Ireland), Potenza (I) and Sodankyla (FI). The stations in Ireland (clean Atlantic air), Italy (Mediterranean), and Finland (Arctic) enable better sampling of the different European regional climates. Evolution of air masses in the prevailing westerly winds can be studied from changes in aerosol and cloud characteristics at Mace Head, Chilbolton, Cabauw, Palaiseau, Juelich, and Leipzig/Lindenberg.
Task 5.2 Additional cloud aerosol variables have been implemented: i) drizzle retrieval in and below clouds, drizzle optical depth, and in-cloud drizzle flux/rain rate. ii) Turbulent kinetic energy dissipation rate iii) (see details below).
Task 5.3 Provision of quantified errors for the observations. Essential for the model performance analysis, and the first step if the observed profiles are, at some future date, to be assimilated into the forecast models so that the forecast is initialized by a better representation of the true state of the atmosphere.
Task 5.4 Implementation of new metrics for evaluating model performance. Evaluating model performance is not a simple matter. Simple parameters such as the mean values of profiles of cloud fraction, cloud water content, and their probability distribution functions are very useful as a general indication of how well the model is performing. A new measure; the ‘skill score’ to reflect if the model has the right cloud in the right place at the right time The commonly used ‘equitable threat score’ is misleading as it depends upon the frequency of the event, but the new metric ‘SEDS – the Symmetric Extreme Dependency Score’ that does not have these difficulties has been implemented.

Summary of results on the shortcomings of cloud representation in operational forecast models:
i) All models underrepresent the frequency of mid-level cloud (3-7 km) by about a factor or two. This serious shortcoming has been known from pre-ACTRIS Cloudnet findings, but there has been little improvement during the past ten years.
ii) It has been suggested that the lack of mid-level cloud might arise from ‘snow’ not being classified as cloud in the model radiation scheme, but Cloudnet analysis shows this is a very small effect.
iii) All models have difficulty producing 100% cloud cover (overcast) for heights below 7 km. For example, over the altitude range 3-7 km the frequency of overcast skies in the models is only 10% of the observed value. This reflects a fundamental difficulty with current schemes whereby cloud fraction depends on the prescribed width of the spread of relative humidity around the mean value within the box, so that, even when mean humidity is 100%, the cloud cover is below 100%.
iv) The new ‘SEDS’ skill score of getting the right cloud in the right place at the right time is actually higher in the 3-7 km height range than < 3 km. This result is, however, spurious. It is reassuring to find that when the profiles are classified by temperature, then there is a much higher SEDS skill score for warm clouds (>0 degrees C) than cold clouds (<0 degrees C). This indicates that the representation of warm clouds in the boundary layer is rather good, and suggests that the difficulty may be that the prescribed rate of glaciation of supercooled clouds is too high. Generally speaking, water clouds are rather persistent, but once ice forms they tend to disperse.
v) The skill scores decline smoothly as the forecast lead times increase from 0-11 hours to 60-71 hours indicating that models do not have a major spin-up problem. For some models, however, there is a shift with forecast lead time in the model climatology for certain variables, indicating differences between the assimilation and forecast model states.
vi) Seasonal changes of the SEDS scores as a function of height, confirm that it is easiest to forecast the position and timing of ice clouds in the winter, presumably because these are formed by widespread synoptically-forced ascent that is well captured by the models. Skill scores are lowest for the position and timing of boundary layer clouds at all times of year and clouds at all heights in the summer, reflecting the difficulty of predicting the precise position of convective updrafts.
vii) Finally, the cloud fraction skill scores, SEDS, for the ‘best’ NWP models show no obvious increase from 2004 to 2015. The spread in skill scores between various models has declined sharply, so that after 2011 the skill scores in all models are virtually identical. One assumes this is as a result of intensive discussions between the various modelling centres so they all adopt the best practice.


The strategic aim of the WP-6 was to ensure the continuity of ACTRIS observations as a part of European future research infrastructures. One of the most important task of WP-6 was related to the actions to bring ACTRIS towards a joint “European Atmospheric Research Infrastructure” (ESFRI process). To support this strategic aim the practical actions were needed to integrate the ACTRIS sites and network components into more coherent and coordinated integrated observation system. WP-6 was also aimed to design and deliver a conceptual design of the prototype core ACTRIS station and to and construct the higher level products. Part of the WP-6 activities were also to enhance the knowledge transfer between different communities (WP2-5) and to facilitate the internal and external communication and to provide training on data analysis and a hands-on use practice on the state-of-the-art infrastructure.
The strategic vision of the future development ACTIS observation system was provided in the ACTRIS ROADMAP, which was released in June 2012 . Based on the roadmap recommendations the ACTRIS SSC and WP leaders started the consulting the initial end-user communities such as the AeroCom, the MACC consortium and the VAL subproject, EMEP and several EU projects in order to indentify the end-user needs for the ACTRIS data products. Also links to a new large-scale research and research infrastructure programmed called Pan Eurasian Experiment (PEEX) were established. One of the main interests of PEEX is the development of the research infrastructures and in situ observation networks in Russia and in China.
ACTRIS process towards a joint European Atmospheric Research Infrastructure was continued via internal query among ACTRIS partners on their national ACTRIS-ESFRI status. In 2014 started intensive preparations in order to submit ACTRSI-ESFRI proposal in March 2015. As part of the “ACTRIS - a joint European Atmospheric Research Infrastructure” -process ACTRIS consortium submitted the new ACTRIS-2 I3-project proposal to European commission in August 2014. As a result of successful evaluation the ACTRIS will continue as the EU H2020 project ACTRIS-2 (Aerosols, Clouds, and Trace gases Research InfraStructure) starting 1 May 2015 for a period of four years.

The actions for the operational integration of sites and network components were focused on the ACTRIS Near-Real-Time (NRT) data collection, processing, and establishing the dissemination infrastructure. The work was inherited from the EU-FP6 project European Supersites for Atmospheric Aerosol Research (EUSAAR). The development of the ACTRIS network data products were developed based on the dialogue with end-user communities (MACC, WMO and EMEP) via joint workshops. As one of the main outcome of this task was the implementation of interface for delivering NRT aerosol data to the European Centre for Medium-Range Weather Forecast (prime user) and establishing the connection between ACTRIS data centre and the WMO Information Service (WIS).

The baseline for the integrating essential components into one prototype - the ACTRIS core station was that there were active research infrastructures operating in the European scale, but at the same time there was a clear need for improving the concept of network of networks that can bring together a much larger set of independent networks into an informal federation of those existing activities. The detailed recommendations for the concept of this type of sustainable network has been indentified. The ACTRIS core station conceptual design covers detailed descriptions of the instruments setups, core parameters, data products and the synergy aspects with the other networks such as ICOS, EMEP and GAW.

Conceptual design and construction of higher level products requires the on hand scientific judgement and consultation of the data providers. Benchmark datasets were used for model evaluation of aerosol transport and climate models were assembled in a bundled form at the Met.No website (http://aerocom.met.no/download/). In a start, the prototype of the first component of the web had an interface to Higher Level products and held the access to higher level aerosol data sets assembled for the purpose of AeroCom model evaluation. Latter it was prepared to hold even larger amounts of benchmark data coming up from ACTRIS. The AeroCom visualization web interface to model evaluation - using these observational data, including ACTRIS data (http://aerocom.met.no/cgi-bin/aerocom/surfobs_annualrs.pl) was developed to provide any expert the information to judge current aerosol modelling. Several important steps were made within ACTRIS to make the optical aerosol data available to better constrain modelled radiative forcing, in particular in AeroCom. The preparation, visualization and testing of vertical profiles of aerosol extinction led to a new climatology of vertical distribution of key parameters over Europe. Trend datasets are now available for download as secondary datasets to test temporal evolution of optical parameters and aerosol number concentrations over the last decades. For the latter ACTRIS secondary datasets have been compiled of aerosol optical properties (Collaud Coen et al. 2013) and of aerosol number concentration (Asmi et al. 2013). Two products are developed in ACTRIS to constrain and evaluate models with respect to aerosol optical parameters: a) A joint benchmark visualization of the ACTRIS aerosol optical parameters and their usage for the evaluation of AeroCom phase II model results and b) a benchmark model evaluation protocol established to make use of the ACTRIS aerosol in-situ optical properties, sent out to the international modelling community. Exemplary surface and satellite data integration was prepared for ACTIRS AOD and satellite data and Earlinet aerosol extinction profiles as compared to CALIOP satellite derived extinction profiles on seasonal basis. The different data and visualizations are all accessible via the ACTRIS data portal (http://actris.nilu.no). The main result of this task was the succescfull development of the all originally planed the higher level data products: Long-term trends of aerosol properties; Climatology of vertical distribution of key parameters over Europe; Radiative forcing benchmark dataset; Satellite & surface data integration tool.

Moreover, University of Helsinki organized several ACTRIS related training course on measurements of atmospheric aerosols at the “SMEAR II” flagship station. During these courses the participants learned the techniques of these measurements, and got familiarized with the measurements on-site and methods of statistical data analysis. Tutorials were organized in the connection of annual meetings during annual meeting to improve knowledge transfer within ACTRIS.


Within ACTRIS transnational access was provided to 11 stations (WP7-WP17) representing research facilities with an excellent combination of advanced instruments and expertise, using state-of-the-art equipment for measurement campaigns and instrument testing.

In the frame of WP7, CIAO has hosted 7 projects: 4 of them have been mainly focussed around the training of PhD students and experienced researcher in the use of lidar (instruments and observations); 3 of them have been hosted with the aim to improve our knowledge of the physical process involving the tropospheric aerosols and to the use of low cost or automatic instruments to retrieve aerosol properties.
For the training projects, the mains results have been represented by the consolidation of existing lidar activities within ACTRIS (e.g. station in Clermont-Ferrand) and outside ACTRIS borders (e.g. Cuba).
The remaining project allowed us to provide the ACTRIS and the whole scientific community with the following results.
1. An extensive test of the performances of three commercial laser ceilometer vs an advanced Raman lidar for the quantitative study of aerosol in the boundary and free troposphere has revealed instability of ceilometers on the short and mid-term time range; therefore, technological improvements are needed to move ceilometers towards operational use in the monitoring of atmospheric aerosols in the low and free troposphere.
2. The study of dust profiles from EARLINET stations and dust models has allowed the identification of potentially interesting observed cases of dust coming from Sahara for modelling case studies and for the improvement of models predicting ice nucleation due to dust nuclei
3. The test of a commercial Raman lidar has allowed to identify problems in the instrument through a comparison with an advanced Raman lidar, allowing its improvements and ensuring an enhanced reliability over longer time periods.
Results from project held at CIAO in the last three months of ACTRIS will outcome by the end of 2015 and shared with the ACTRIS community.

In WP8, SIR-2 and SIR-3 TNA projects allowed two PhD students (one from ETH Zürich, Switzerland, and one from U. Münster, Germany), to develop the datasets they needed to carry out their PhD investigations. By accessing the SIRTA observatory, the two PhD students were able to deploy their experimental setup and to access to all measurements necessary for their research. The students finalized their PhD thesis in 2014 and 2015, respectively. Three peer-reviewed publications mentioning the support of the ACTRIS project were published in 2014 and 2015. SIR-5 TNA project allowed training of a PhD student from the U. of Sofia, Bulgaria, and provided the student with access to data necessary for him to carry out his research.
SIR-4 TNA project allowed several users to participate in the first international intercalibration campaign of Aerosol Chemical Speciation Monitors (ACSM). This campaign demonstrated the possibility to carry out such inter-comparison, and validated the methodology. It is the basis upon which an ACSM calibration service is now included in the ACTRIS-2 European aerosol calibration services.

In WP9, 3 projects were related to the analysis of the first data from the new solar-observing Fourier-transform infrared spectrometer (FTIR) installed in the new high-altitude observatory on the Maïdo mountain on Reunion Island in March 2013. This Maïdo observatory is one of very few multi-instrumented stations in the Southern hemisphere, which all contribute data to various international observation networks. Focus has been done on the comparison of the analyzed FTIR data obtained at the Maïdo altitude station and the second instrument at sea level in order to extract informations on the gaz composition (CO, CH4, and CO2 measurements) of the boundary layer and lowermost troposphere between the two stations. The WV-PROFILES-MAIDO project was focused on the crucial role of water vapour as a climate variable. It strongly controls the energy budget of our planet via its greenhouse effect (e.g. Kiehl and Trenberth, 1997). It plays a key role in many aspects of UTLS chemistry, e.g. being the main precursour of HOx radicals contributing to the catalytic destruction of ozone in the lower stratosphere (e.g. Wennberg et al., 1994). Stratospheric water vapor is an important driver of decadal global surface climate change (Solomon et al., 2010). The scientific objective of this project is the analysis of accurate measurements of water vapour in vertical profiles performed at the Maïdo observatory in the framework of NDACC (Network for the Detection for Atmospheric Composition Changes) and ACTRIS programs during the MORGANE (Maïdo ObservatoRy Gaz and Aerosols Ndacc Experiment) field campaign. Reunion Island is appropriately located to monitor, how most air enters the stratosphere in the tropics (Holton et al., 1995) by a combination of rapid vertical motion in convection and slow diabatic ascent. Upper-air soundings of water vapor in the tropical band are of great interest as water vapor is a crucial climate variable.

The TNA activities to SMR (WP10) included all the components of the ACTRIS project, from emissions and concentrations of trace gases, aerosol physical, chemical and optical characterization, to aerosol vertical profiling with active remote sensing from ground level. A brief overview of the main results are given here.
Trace gases, aerosol precursors: in the OVOC-TOOC project an intercomparison of organic trace gas concentration measurements was performed. The results indicated a good agreement between the techniques (Kajos et al. 2015). Volatile organic compounds emitted by the biosphere oxidize in the atmosphere and form vapors that condense onto pre-existing aerosols or even form new aerosols. The results of ABSOA and DIMER (PI Glasius) measured and identified several organic acids and organosulfates of both biogenic and anthropogenic origin as well as three dimer esters from monoterpenes. Subsequent laboratory experiments probed into hygroscopicity and cloud condensation capacity of the organosulphates (Hansen et al. 2015).
Aerosol physical characterization, aerosol chemical composition, new particle formation and particularly aerosol measurements in sub-10 nm size range: within ACTRIS, the TNA activities were linked to large European research projects (PEGASOS) or US Department of Energy funded “BAECC”, (Petäjä et al. 2015). Pooling of resourced maximized the scientific outcomes. The TNA activity SDA ms-pulses (PI Seran) probed into the role of ionizing radiation and ion cluster formation, which brought novel instrumentation to SMR enabling detailed information on molecular ions and their variation at the site. MOVING (PI Massoli) and TOTAL DETECTION (PI Winkler) performed detailed on-line analysis on atmospheric nanoparticle composition and number concentrations in sub-3 nm particle size. The results underlined the importance of organics in the aerosol growth to cloud condensation nuclei sizes.
Aerosol optical properties: WetNephAtHyytiälä brought gap-filling instrumentation to SMR during PEGASOS Northern Mission. It was investigated the influence of water uptake on the particle light scattering at SMR with the following outcomes: 1) the scattering enchancement f(RH) was low in biogenically dominated region. The columnar closure was quite well established.
Vertical profiling of aerosols and clouds: Three TNA activities (SACS-BAECC, POLLY-XT at BAECC and BAECC-ERI,) were conducted during BAECC intensive providing unprecedented vertical profiling of aerosols, clouds and precipitation at SMR. These projects provided key observables and enabled comparison of European and US standard procedures for aerosol and cloud retrievals from ground-based remote sensing instrumentation. BAECC-ERI detected supercooled liquid layers, cloud condensation nuclei and cloud electrical properties with novel radiosondes. The analysis of these results are on-going, but the comparison against ground-based remote sensing has already been fruitful (Petäjä et al 2015).

The TNA opportunity for CESAR Observatory (WP11) has attracted activities across the full range of the ACTRIS domain. Researchers have visited the site to do experiments for trace gases, aerosols and cloud, albeit that the intention varied from training to learn about advanced instrumentation to participation in campaigns by bringing complementary instruments to the observatory. In particular young scientists used the TNA instrument to perform their research and built their network. The TNA-instrument has increased the mobility of the involved researchers, and has led to new scientific results – for example a deeper insight into how ice crystals grow when falling through super-cooled liquid water layers. The added value of TNA activities also manifested itself in the results of the regular work packages of ACTRIS: the collected data showed striking examples of cloud-aerosol interaction, and enabled a deeper insight into the quality of retrieved cloud properties. The TNA-instrument contributed significantly to the error characteristic of the observations and therefore to the quality of ACTRIS.

The impact of aerosols on climate via cloud formation remains to be an area of large uncertainty. Field measurements are required to further elucidate the importance of the various involved problems. This is especially the case for mixed-phase and glaciated clouds as it is very difficult to simulate all involved processes in the laboratory. While aircraft measurements have the advantage that they can fly to regions where clouds of interest are present they are limited by observation time. Ground-based measurements are therefore an indispensable means to study these processes. The Jungfraujoch (JFJ) is one of the very few places worldwide where such glaciated clouds can be studied in situ, with an infrastructure providing easy access throughout the year and the required space to perform the experiments. Not surprisingly, the majority of TNA accesses to the JFJ within ACTRIS (WP12) have focused on this topic. With innovative instrumentation the chemical and physical properties of ice residuals (which are thought to be the ice nuclei in small ice crystals) was determined. Another important result was the demonstration of the high inhomogeneity of clouds, with alternating pockets of liquid and glaciated clouds, adding further complexity to the cloud treatment in models. The experiments have not only been performed at the JFJ but in one case also at the Schilthorn (2970 m asl, 10 km air distance from the JFJ), as an out-of-cloud upwind site. The results will also serve as input to an explicit cloud-aerosol interaction model (ACPIM). If successful, these results are expected to strongly contribute to a further reduction of the uncertainties related to the aerosol impact on clouds and climate.
A second important topic area was the investigation of new particle formation in the free troposphere. New instrumentation has recently become available which allow today to study the involved processes with unprecedented detail. The results will be highly important in the comparison with results from recent laboratory results e.g. by the CLOUD collaboration at CERN.

TNA access was provided to Mace Head (WP13) which is the main marine research station in the ACTRIS network and is exposed to the clean NE Atlantic westerly air flow for about 50% of the time. The remainder of the time it is exposed to the most polluted continental air to modified marine and modified continental conditions. The TNA activities at Mace Head ranged from single individual access projects to one large-scale campaign. Studies included Reactive Iodine and Particle formation (RIPO), carbon isotope studies, Doppler Lidar/Radar studies and Marine aerosol formation and impacts on clouds (MaCloud). Countries accessing the facility included Finland, Germany, France, UK, Lithuania, Denmark. The majority of the TNA usage occurred early in the project because of the size of MaCLoud and the timing of MaCloud which was scheduled to avoid clashes and commitments with other international campaigns. The scientific outputs are listed on the ACTRIS website. They can be summarised as making significant advances in direct quantification of iodine oxidise involved in coastal new particle formation, evaluation of the role of organics in open ocean new particle production, the role of sea-salt in cloud droplet activation, and quantification of organic aerosol sources using isotopic methods.

AMO (WP14) supported a total of five TNA projects, three of which had training elements, two of which supported PhD students and two included elements of instrument intercomparison / validation: the project NH3measurement trained a visiting PhD student from BOKU, Vienna, in the measurement of NH3, using the instrumentation at AMO. This project has enabled BOKU to add NH3 as a further compound to laboratory studies of trace gas emissions from soils and leaf litter. AMEXME trained a visitor from the Univ. Politecnica, Madrid, in the operation of a wet chemistry gradient analyser for NH3 flux measurements. A similar instrument was then borrowed from NERC CEH to make the first NH3 flux measurements above Spanish vegetation. NOMAS funded the University L’Aquila to operate of a TD-LIF instrument for NOy compounds at AMO, during a nitrogen intensive measurement campaign. In addition to delivering measurements on NOy compound groups not usually measured at AMO and fluxes of NOy, this project provided useful information on artefacts of both the ongoing wet chemistry measurements at AMO and the TD-LIF. The OrganicN wetdep project provided access for a Spanish PhD student from the University of Navarra to AMO and the NERC CEH analytical lab to analyse wet deposition samples from AMO and Spanish fieldsites for total N and, by difference, organic N. The measurements showed that organic N makes a significant contribution to N wet deposition at the Spanish sites, whilst chemical analysis of the inorganic fraction at AMO is ongoing. Finally, the FOSE project supported scientists from the Catholic University at Brescia, Italy, to set up instrumentation for an intercomparison of fast-response flux sensors for O3. Analysis is ongoing.

At FKL (WP15), six TNA projects were selected and carried out during the entire period representing a total of 131 access units (research-person working days), i.e 31% above the initially planned number. The purpose of the first TNA project (FAME-2011) was to better characterize organic aerosols (OA) and gas precursors (sources and properties) in the Eastern Mediterranean during a period of the year (falls) when photochemistry offers the best conditions to investigate OA having different oxidation states. The aim of the second (POPLRTMED) was to advance the understanding of POP cycling far from sources by addressing key processes in the marine boundary layer in air masses characterized at a receptor site and influenced by regional and remote sources (concurrently with measurements at other sites in the receptor region. The aim of project Nutrient-solubility was to understand the factors controlling the amount of the soluble (<20nm) and dissolved (<200nm) Fe and/or P in rainwater deposited to the oceans and answer to key questions related to biogeochemical Fe cycling such as i) the processes controlling the concentration and partition of labile, soluble and dissolved Fe and P in dust from rainwater and ii) to clarify how Fe interact with P and trace metals in rainwater and affect their solubilities; The aim of the fourth project Volatile Organic Compound measurement Campaign in Crete, VOCCC was to understand ropospheric ozone (O3) and secondary organic aerosols (SOA) formation as a consequence of the degradation of atmospheric volatile organic compounds (VOCs). The general objectives of the fifth and six ADAMA and VAMOS-UAV projects were to derive optical, microphysical and chemical properties of the aerosol marine component and its mixture with dust, employing sophisticated instrumentation installed on Finokalia ACTRIS site. Specifically, aerosol characterization was studied by using ground‐based active/passive remote sensing techniques, surface in‐situ measurements and airborne UAV observations. The PMOD/WRC participated in the campaign providing spectral, high frequency AOD measurements with a new Precision SpectroRadiometer (PSR_003).

The scientific results of the WP 16 TNA projects have been strongly linked to side-by-side intercomparison activities at the GAW Global Station Hohenpeissenberg. Goal of these intercomparsions was to assess the current quality of ACTRIS stations to determine OVOC and NOx in simple and challenging synthetic test gas mixtures and in ambient air matrix. 16 state-of-the-art routine and research instruments participated in the NOx-, and 10 in the OVOC-intercomparison.
The side-by-side intercomparison of NO and NO2 was with participation of four TNA projects (HPB 1-3 and 6). In synthetic mixtures, deviations from reference values were generally < 3% for NO and < 5% for NO2. Ambient air measurements show partly substantial deviations, mostly due to issues with calibration, converter efficiency, or system malfunction. All instruments equipped with Mo converters failed for NO2 with too high mixing ratios. The ACTRIS/GAW-DQOs (level 1) are accessible with commercial CLD instruments as long as trace level instruments with pre-chamber and high-level QA are used. NO2 by direct methods (CRDS, LIF, CAPS, and CEAS) proved to be similar or better than by CLD.
The OVOC intercomparison at DWD-Hohenpeissenberg was with participation of three TNA projects (HPB 7-9). Measurements of the non-oxygenated VOC benzene, toluene and isoprene and the ketones acetone and MEK showed a good agreement between all instruments. For methanol, three GC systems showed high losses in ambient air measurements. For acetaldehyde clear deviations among the instruments were observed in both synthetic and ambient air with the GC systems often reported higher measurements than the PTR-MS. PTR-MS seem to better determine the critical OVOC compounds, however, drifting background and deviations between instruments at trace levels are issues. In contrast, GC based systems are able to resolve compounds with the same masses, however, are sensitive to surface-contact related artefacts.

In WP17, 107.5 days of access to RADO were provided (out of 95 days estimated at the project beginning) , within 4 TNA projects to 6 users:
- ARELISSES -Aerosol direct Radiative Effect based on LIdar and Sunphotometer measurements in an Eastern European AERONET/EARLINET Site.
- ACLIMEEA - Aerosols Classification by Lidar and ground based Measurements over Eastern European AERONET/EARLINET Site.
- ECAD - Error estimation in calibrated depolarization lidar measurements.
- QAT4LUW - Quality Assurance Training for Lidar operation at University of Warsaw.
A combination of theoretical and experimental research using available infrastructure at RADO, basically the multiwavelength depolarization Raman lidar have been performed during the TNA. Training sessions related to lidar (alignment, operation, inversion algorithms, data processing, specific tests - telescope cover, Rayleigh fit, depolarization calibration, data pre-processing) and instrument's performance; Hysplit, DREAM and MODIS synergetic approach for case studies have been offered to users. The correlation of the aerosol type and corresponding properties, in various atmospheric conditions at RADO, as well as evolution of the air flow properties thorough Poland and Romania and calibration methods influence of the lidar system polarizing sensitivity are main results obtained.
Several common proceeding /peer review papers are under preparation or submitted to journals. Also several results have been presented to conferences/workshops.


Within ACTRIS, TNA was provided also to the AERONET-EUROPE Calibration Service (WP18). The scientific fields covered by AERONET-Europe (AE) activities are of interest for a wide ensemble of users belonging to the academic world, to the operational world (including national meteorological service, air quality agencies, atmospheric modelling groups, space agencies, and aviation requesting volcanic ash wildfires and dust monitoring), to the industrial world (with SMEs manufacturing sun-photometers and LIDARs, with SMEs contracted by Space Agencies for data processing and finally, with SMEs involved in solar energy plants).
Thanks to EC funding, AE offered, since 2011, a unique calibration/maintenance/training remote TNA for CIMEL sun/sky photometers but, also, for other existing and in development technologies ranging from research to industrial projects (CIMEL & PREDE SMEs). As the AERONET network grew, AE Calibration Facility, managed by France (LOA/CNRS/Univ. Lille), in cooperation with Spain, took over almost all European calibrations under the ACTRIS umbrella. This highly helped AERONET to become a standard for aerosol research including validation of satellite remote sensing, model forecasts, multi-instrument data combination, etc…. Aerosol parameters produced by sun/sky photometers calibrated by AE are extensively used by the modeling community (eg. MACC-II, GMES Atmosphere Service) and by space agencies (for validation of satellite products, eg. CCI projects). AE also provided calibration access, through cooperative projects, to Northern Africa users and for reference instruments of AERONET-equivalent networks operating in China (CARSNET/CMA, SONET/CAS). The result has been an extremely accurate and dense network of sun/sky photometers providing near real-time aerosol properties at a scale commensurate with local, regional and global aerosol processes. Finally, additional development of a low cost handheld sun-photometer has been also performed for pedagogical purposes (TENUM/CALITOO SME).
Users and operators AE, now familiar with the TNA organization, all together contributed to (i) increase visibility and use of AE, (ii) favour the European capacity and autonomy, (iii) the integration of complementary communities, (iv) shape the new European identity of AERONET. For the future (ACTRIS-2), one can anticipate that network will become a new type of user, as for example, the future joint LIDAR/sun-photometer network from UK Met Office.


ACTRIS data centre (ACTRIS DC) (WP19) is a service activity aiming to act as a long-term sustainable data centre. It provides free and open access to all ACTRIS data resulting from the activities of the infrastructure and is complemented with data from other relevant networks. Furthermore, the service activity makes tools and applications available to the scientific community and other user communities, which facilitate the use of network data.

The overall goal of the ACTRIS Data Centre is to provide scientists and other user groups with access to the ACTRIS infrastructure data.

ACTRIS variables, ACTRIS data, and the ACTRIS Data Policy
An important fundament for efficient data management and provision of ACTRIS data was to work on an agreement across the consortium with a detailed overview of the ACTRIS variables, methodologies, and data based on the work in the various networking activities. Based on thorough discussions within the scientific steering committee and the consortium, this was established and is available here
http://www.actris.eu/Portals/97/Publications/data%20concept/ACTRIS_data_concept.pdf. Secondly, an open data policy is crucial for extensive use and access to data. The ACTRIS data policy and description of data management was approved by the consortium and is available online: http://actris.nilu.no/Content/Documents/DataPolicy.pdf. These documents are both important achievements and a fundamental for advanced and efficient data managements.

Highlights of ACTRIS Data Provision
The overall goal of the ACTRIS Data Centre relies on efficient data management and data flow from the contributing sites and measurement communities to the final user. Large efforts have been put into this to maintain, strengthen and ensure data flow from the data providers to the data centre and archiving of the data. The numerous measurement methodologies applied in ACTRIS, more than 25, result in a considerable diversity of the data collected. In accordance with these requirements, the measurement data contributing to the ACTRIS Data Centre are archived in three stand-alone topic databases, which are all linked in the ACTRIS data portal: http://actris.nilu.no. The topic databases are:
- EBAS for near surface aerosol and trace gas data http://ebas.nilu.no/ ,
- EARLINET DB for aerosol profile data: http://access.earlinet.org/EARLINET/
- CLOUDNET DB for Cloud data: http://www.cloud-net.org/data/

Quality controlled and quality assured data are submitted by the instrument principle investigators on an annual basis. As of 31 March 2015 the data management system in ACTRIS has compiled QC and QA ACTRIS measurement data from 66 sites and approximately 120 different atmospheric variables from 28 various instruments and methodologies. The variables include almost 90 different trace gases, 10 aerosol in situ variables, 8 aerosol profile variables and 8 cloud profile variables, with various time resolution. For almost 30 of the ACTRIS variables near real time (NRT) data flow is set up with direct interface between the data centre and the instrument. Currently ca 12 sites and 29 associated sites provide NRT data.

At the end of ACTRIS, the comprehensive ACTRIS data management of ground-based atmospheric data is unique in both the European and global perspective, documenting the archiving and access to data from a high number of sites, instruments and variables available through one portal. Continues support with a strong link between the data centres and scientific communities as well as the ACTRIS networking activities have proven to be the most important factor for successes with data flow, collection, documentation, quality assurance and archiving the data.

Examples of data access and user statistics
Monitoring the use of ACTRIS data from the data centre show the following core metrics since the start of ACTRIS:
- Near surface aerosol and trace gas data: More than 49 000 time series are downloaded and more than 12 500 time series are plotted and inspected in the data base. This performed by 1900 unique users from 68 countries distributed globally. One data set is one variable, independent of time period (full time series of 1 variable since measurement start is one data set 1 (e.g. 10 years of data with high time resolution count as 1)
- More than 1 400 200 aerosol profiles are downloaded by 210 unique users distributed globally from more than 36 countries. One data set contains at least 1 profile of one variable, it may contain of profiles covering up to 24 hours.
- For cloud data there are 66 external users, not involved in Cloudnet itself.

The MACC project has been using ACTRIS data for model evaluation, and data from ACTRIS appeared regularly in the three monthly validation reports from MACC. Furthermore, experimental usage of surface aerosol scattering coefficient was done to explore the use of this other source of near real term data from ACTRIS super sites.

Integration, interoperability, access to tools and secondary data products,
During ACTRIS all three topic databases archiving the measurement data were linked together by the ACTRIS data portal: http://actris.nilu.no. This was the first and essential integration step providing the joint portal for access to all ACTRIS data. The portal has developed during the project and it includes various tools to combine data across the topic databases.
Examples on functionality in the portal
- Dynamic maps for visualization of distribution of sites and variables. The maps provide tools for an easy overview of collocation of variables, sites and complementary data.
- Pins on the map contain relevant information about the sites, and point directly to the download via the links provided in the respective information boxes.
- Online analysis and plotting of ACTRIS data is implemented combining aerosol profiles with ground based data. Temporal colocation of profiles are visualised in time series plots of ground based data.
- Access to secondary data products and project data tools. This page includes a directory to the ACTRIS archive for secondary data sets (aggregated data) and project data tools (e.g. programs that have been used to generate secondary data from primary datasets). Archiving of both, secondary data products and project data tools, is set up and made available.
- An interface to ACTRIS data shown together with AEROCOM model products for comparison of model and ground based data is implemented in collaboration with WP6. The ACTRIS-AEROCOM data products for aerosol forcing, surface-satellite data, trends, and vertical profiling can be accessed directly through the ACTRIS data portal, and the model outputs can be compared to relevant ACTRIS data.

Interoperability with other data centres: The ACTRIS research data management is unique worldwide in the sense that it uses modern data architecture concepts for covering a diverse set of observed quantities. This has been highly prioritized, and the architecture of the ACTRIS DC is not only adapted to the federated nature of the European research area, but also to the governance of international research frameworks, and can directly contribute to these, strengthening the European position in these frameworks. The ACTRIS DC is therefore suited to contribute to, e.g. the European Copernicus programme, here also with products in near-real-time, and international frameworks such as the WMO Information System (WIS) and the Global Climate Observing System (GCOS). ACTRIS DC metadata is INSPIRE- and WIS-ready, and offers a framework for data reporting traceable to the time of measurement, as well as for logging the version history of a data resource.


The Joint Research Activity on “Lidar and sunphotometer — Improved instruments, integrated observations and combined algorithms” (WP20) achieved significant progress in the integration of two major well-established aerosol observation networks, the European Aerosol Research Lidar Network EARLINET and the European part of the Aerosol Robotic Network AERONET. In this way, improved observational capabilities for the characterization of the four-dimensional aerosol distribution over Europe were established. In particular, the partners worked towards
- the improvement of daytime capabilities of lidar instruments with emphasis on easy-to-implement solutions and continuous operation,
- the development and application of integrated observation strategies for lidar and sunphotometer instruments to gain complementary information on atmospheric aerosols, and
- the retrieval of advanced information on aerosol microphysics from multi-spectral, multi-angle columnar sunphotometer and height-resolved multiwavelength lidar observations under consideration of polarization information.

Daytime extinction measurements with Raman lidars
So far, most ACTRIS stations apply the Raman lidar technique for measurements of aerosol extinction only at night time, whereas passive observations are made with sunphotometers during the day. In order to make better use of the instrument synergy, these limited observing capabilities should be overcome. Therefore, in the course of the project, the most advanced technical solutions for daytime aerosol extinction measurements with Raman lidar systems have been assessed and tested. As a result, solutions based on either interference filters or grating spectrometers to efficiently separate the rotational Raman spectrum of nitrogen and oxygen from elastic lidar returns and daylight background are recommended for implementation at combined ACTRIS lidar and photometer stations. Together with the new lunar photometer technology, which became available only recently, it will be possible to perform combined observations with active and passive remote-sensing instruments synchronously at day and night in the near future. This new observing capability also builds a basis for further integration strategies at ACTRIS supersites.
New algorithms for combined lidar and sunphotometer data
New combined retrieval schemes elaborated in this Joint Research Activity allow for the optimum use of the synergistic information from active and passive remote sensing. Two inversion algorithms have been developed, tested, and implemented in order to obtain advanced information on aerosol microphysical properties. The first one is the Lidar/Radiometer Inversion Code (LIRIC) from the Institute of Physics of the National Academy of Science of Belarus, Minsk. The second one is the Generalized Aerosol Retrieval from Radiometer and Lidar Combined data (GARRLIC) designed at Laboratoire d’Optique Atmosphérique, Lille (Lopatin et al., 2013). The concepts of the two algorithms are slightly different. Whereas LIRIC makes use of final sunphotometer products of column aerosol microphysical products and multiwavelength lidar signals, GARRLIC starts with sun and sky radiances measured with radiometer and performs a complete new inversion of both radiometer and lidar data together. The basic algorithm versions require at least three elastic-backscatter lidar signals at 355, 532, and 1064 nm. Advanced versions of LIRIC process Raman and/or polarized signals in addition. Inversion products comprise profiles of fine-mode and coarse-mode particle volume concentrations. When polarization information is available, the spherical and non-spherical particle fractions can be calculated. A new product available from GARRLIC is the spectrally resolved profile of the single-scattering albedo.

Integrated observations
Integrated observation strategies for EARLINET multiwavelength lidars and AERONET sunphotometers have been applied to provide datasets for the development and test of the combined inversion algorithms. In order to cover a broad variety of aerosol types and their different mixing states, six EARLINET-AERONET stations, out of currently 22 available combined sites in Europe, were selected to perform dedicated observations in five European core regions (Central Europe: Leipzig, East Europe: Minsk, Spain: Granada, Italy: Potenza, Greece: Athens and Thessaloniki). Specific measurement cases from each station have been collected in a common database. This database is hosted by the National Observatory of Athens and publicly available at http://lidar.space.noa.gr/lidar_db/. Currently, it contains more than 120 quality-assured combined data sets from a large variety of atmospheric scenarios covering, e.g. dust outbreaks, pollution episodes, and smoke events. Users can download these datasets for evaluation purposes and can upload test results obtained by the application of the combined algorithms.

Algorithm evaluation and applications
ACTRIS partners applied the LIRIC and GARRLIC algorithms to a large variety of measurement cases covering different aerosol scenarios over Europe. Several studies concerned parameter settings and constraints of the retrieval schemes (Wagner et al., 2013; Granados-Muñoz et al., 2014). Generally, it turned out that the algorithms are well suited to distinguish fine-mode aerosol, i.e. pollution and smoke, from coarse-mode particles induced, e.g. by Saharan dust outbreaks, and to deliver the respective profiles of volume or mass concentrations throughout the troposphere. However, care has to be taken when the aerosol mixing situation is very complex, since the algorithms do not consider a variation of the coarse- and fine-mode microphysical properties with height.
Several validation studies using in-situ measurements from ground and aircraft have been performed. Comparisons with airborne observations became possible for the Greek stations in the frame of ACEMED (Evaluation of CALIPSO’s aerosol classification scheme over Eastern Mediterranean; the project was realized through EUFAR Transnational Access). At Granada, observations were carried out with photometers placed at different altitudes on nearby mountain sites (Granados-Muñoz et al., 2014), and complementary in-situ measurements of particle microphysical properties from aircraft and at ground were used to validate the combined lidar-sunphotometer retrievals of microphysical properties.
The capability of deriving separated volume concentrations of coarse non-spherical particles is particularly useful for the quantification of atmospheric dust and ash loads (Tsekeri et al., 2013). Therefore, a number of studies dealt with the investigation of Saharan dust and volcanic ash concentrations. For instance, four different Saharan dust transport models have been evaluated by using more than 60 combined retrievals with LIRIC, applied to measurements at 10 EARLINET/AERONET stations in the presence of Saharan dust (Binietoglou et al., 2015). In another application, the effect of mineral dust on the longwave direct aerosol radiative forcing was investigated (Sicard et al., 2014). The LIRIC algorithm has also been applied to previous measurements of the Eyjafjallajökull volcanic aerosol plume in April/May 2010 (Wagner et al., 2013; Kokkalis et al., 2013). In this case, it was possible to clearly separate the contributions of coarse ash particles, which are hazardous for aircraft engines, and rather harmless fine sulphate particles, both stemming from the volcanic emissions.
The potential of combined lidar-sunphotometer observations and retrievals has been demonstrated through various other applications. For example, combined lidar and sunphotometer aerosol observations together with cloud measurements by radar and microwave radiometer have been performed during the field campaigns of the German HD(CP)2 project (High definition clouds and precipitation for advancing climate prediction) to study aerosol-cloud interactions. LIRIC was used for the investigation of aerosol hygroscopic growth effects in the planetary boundary layer at Granada, and it was shown that fine-mode volume concentration show a stronger increase with increasing relative humidity than coarse-mode volume concentrations (Granados-Muñoz et al., 2015). Other studies concentrated on the investigation of mixed-type aerosols and comparisons with regional transport and air-pollution models (Papayannis et al., 2014). The GARRLiC algorithm was applied to observations during the Characterization of Aerosol mixtures of Dust And Marine origin Experiment (CHARADMExp), an ESA-funded campaign performed at the ACTRIS station of Finokalia, Crete, in June and July 2014.


The Joint Research Activity on “Comprehensive gas phase and aerosol chemistry” (WP21) was mainly devoted to the evaluation of the ACSM (Aerosol Chemical Speciation Monitor) for continuous aerosol chemistry measurements and OVOC measurements and mass closure of atmospheric organic carbon.

Evaluation of the ACSM for continuous aerosol chemistry measurements
Aerosol chemistry has so far been performed in networks only off-line based on filter analysis. Concerning the organic aerosol, only a sum parameter (total organic carbon, OC) has been determined on a regular basis. There has therefore been a long-standing need for data with higher time resolution and with more information on the organic aerosol than just OC. The newly developed ACSM (Aerosol Chemical Speciation Monitor) is a new instrument which allows on-line measurement of the total mass and size distribution of non-refractory chemical composition of the submicron ambient aerosol. It has the same quantification and speciation capabilities as the aerosol mass spectrometer (AMS), by also providing composition information for particulate ammonium, nitrate, sulphate, chloride, and organic mass concentration. However, it is designed to be simpler, smaller, lower cost and capable of autonomous operation, while still capable of delivering data with a time resolution of 1 hour or lower. Through the statistical analysis of the mass spectra, also source apportionment of the organic aerosol has become possible. This instrument was therefore perceived to have a high potential to fill this measurement gap.
For this reason, the performance and suitability of the ACSM for continuous aerosol chemistry measurement was assessed at the following sites within Task 21.1: Mace Head, Cabauw, Melpitz, Hyytiälä, Finokalia, and Jungfraujoch. At each site, particulate ammonium, nitrate, sulphate, chloride, and organic mass concentration were measured, for a full year. This activity had a huge additional benefit on the European aerosol chemistry research community. A large number of additional institutions decided to contribute with their own funds to this ACTRIS activity. To facilitate the process, a website has been established by PSI, where the progress of these ACSM activities can be monitored: http://www.psi.ch/acsm-stations/
Quality assurance was tested in many different ways. On the one hand, a document was started describing the best practices, which has continuously been updated (the latest version is found at http://www.psi.ch/acsm-stations/acsm-best-practice). This best practice document for ACSMs contains recommendations for operation of ACSM instruments within the ACTRIS network. The purpose of this document is to provide guidelines and standard operating procedures for data recording and treatment in order to ensure data quality and comparability. Moreover, an intercomparison was performed in Paris, which included 13 quadrupole ACSMs, 1 time-of-flight ACSM, and 1 AMS. The results soon to be published indicate the ACSM instruments measurements generally match well both when measuring absolute mass concentrations and sample mass spectra. The study also raised important issues relevant to the wider AMS and ACSM user communities to further consider, especially relating to use of markers and proxies to estimate aerosol oxidation state. The data obtained additionally provided further practical guidelines for calibrations and data analysis.
The suitability for long-term measurements as well as the upload of data to the ACTRIS database have been documented in two Deliverables (D21.3 and D21.6).

OVOC measurements and mass closure of atmospheric organic carbon
In comparison to NMHCs (non-methane hydrocarbons, i.e. alkanes, alkenes, aromatics) continuous measurements of OVOCs in the atmosphere are challenging when using gas chromatography with mass spectrometry (GC-MS) or flame ionization detection (GC-FID) because OVOC tend to show artefacts in the complex sampling and analysis systems. Therefore, OVOCs measurements by surface-contact-free proton transfer mass spectrometry (PTR-MS) were considered favorably in the last years. Despite undisputed strengths of PTR-MS, this method has also some drawbacks (e.g. restricted resolution of molecules with the same molecular mass, drifting background signals, and high costs). Therefore, the aim of task 21.2 was to develop a GC based method for the continuous analysis of OVOCs at remote sites. DWD and EMPA have independently developed measurement methods within the first 18 months of the project, which then were tested at the side-by-side intercomparison at Hohenpeissenberg (Germany) against existing PTR-MS instruments and grab sampling methods. Results were encouraging but also pointed out some problems especially with methanol and acetaldehyde, and will be published in a peer-reviewed journal (Englert et al., AMTD, in preparation, 2015).
First data sets with measurements of OVOCs have been submitted to EBAS under ACTRIS with a preliminary QA/QC-procedure from the ACTRIS sites Birkenes II, La Tardière and Peyrusse Vieille. This data will in the future be supplemented by measurements with newly developed instruments from Hohenpeissenberg (D) and Rigi (CH) and existing PTR-MS measurements from Hyytiäla (SF).
For the mass closure of particulate and gaseous organic compounds in the atmosphere of different European sites proposed in Task 21.3. several data sets from measurement campaigns (e.g. EMEP intensive campaign in 2012, MEGAPOLI) and continuous measurements were re-analysed. Measurements of gas and particle phases of organic carbon compounds were combined to scrutinize the total observed organic carbon (TOOC) in the atmosphere. Gas phase organic compounds are summarized under the term volatile organic compounds (VOCs), whereas organic particles are comprised of a wide range of organic aerosols. This TOOC approach has been further developed in the last year of the ACTRIS project.
Sites ranged from city centers (e.g. London, Paris) to rural and remote sites (e.g. Revin, France; Hohenpeissenberg, Germany). Results are shown in the delivery D21.5 “Report on mass closure experiments performed at 2 European sites”. In addition to the 2 proposed sites, data from a total of 5 sites were analysed. For all sites the gaseous components were always dominant in comparison to the organic particles. In winter the carbon mass concentration is generally higher compared to summer with values reaching nearly 80 µg C/m3 in London. In summer, the carbon content goes up to nearly 55 µg C/m3. The higher winter values are probably due to additional anthropogenic emission sources typical of the winter season (e.g. biomass burning) and to meteorological conditions. For the remote site of Cap Corse the C-concentration derived from aldehydes is much higher compared to other remote sites like Hohenpeissenberg (HPB) or Revin.
In general, the TOOC approach could be tested using measurement data from both urban and suburban sites. Gaseous compounds were dominant, similar as observed in comparable studies in the US.


The Joint Research Activity on “A framework for cloud-aerosol interaction studies” (WP22) was devoted to develop an observational framework for cloud-aerosol interaction studies in Europe and more specifically:
- To develop optimized sensor-synergetic algorithms for the physical characterization of clouds and aerosols in the context of cloud formation and its impact on climate change.
- To develop and test observation strategies for the study of cloud-aerosol interaction studies through combined use of remote sensing, in situ observations and atmospheric models.

Scheme for Monitoring Aerosol - Cloud Interactions
The activity was focused on the formation of an optimal observation scheme of aerosol-cloud interactions. Although a broad range of strategies to quantify the interactions between aerosol and cloud already exists, different scales and methods used make it difficult to compare the results of those investigations. Thus, the main goal was to develop a scheme that would be easy to implement at various cloud-profiling observatories of the ACTRIS network.
The current stations make high resolution observations of vertical profiles with cloud radar, ceilometers, and microwave radiometers. The combination of those instruments provides the necessary information for the evaluation of the interaction between aerosol and clouds. For quantifying the concentration of aerosol below the cloud it was used an integrated value of the attenuated backscatter coefficient derived from ceilometer measurements. Information about the cloud droplets (concentration and size) is obtained from the height-integrated radar reflectivity factor. In addition, we use the retrieval of liquid water cloud properties (Knist, C.L. 2014) to obtain the microphysical characterization of the clouds. This retrieval is also based on the combined measurements from radar, lidar and microwave radiometer. In order to be sure that the first indirect effect has been observed. There is a need to put a constraint on the amount of water available in the column under consideration. For this it was used the liquid water path (LWP) provided by the microwave radiometer.
It was assumed that the number concentration of cloud droplets is related to the number concentration of the aerosol below the cloud. If that is the case, then it is expected to observe aerosol-cloud interaction when the attenuated backscatter coefficient below the cloud is increasing at the same time as the cloud droplet effective radius.

Case study - Cabauw observatory - 2014-10-02
The presented method for monitoring Aerosol-Cloud Interactions is very dependent on an appropriate case selection. The main selection criteria include:
1) Boundary layer liquid water clouds only;
2) No precipitation in the profile - including drizzle; We use the CLOUDNET categorisation to eliminate profiles with the presence of drizzle.
3) Liquid water path above 15 g/m2 and below 150 g/m2;
4) Cloud base is below 2000 m.
The main goal was to be able to account for the impact of aerosol on a persistent stratocumulus layer. The study case from the Cabauw Observatory presented below complies with the majority of those requirements. During the selected time (between 14.2 and 15.8 on 02.10.2014) there were short periods of drizzle, however, they were filtered from the data through applying filtering based on the Cloudnet categorization.
The level at which the data from radar and lidar are compared is based on the distance from the cloud base. The cloud base height was estimated from the lidar measurements. The concentration of aerosols taken for the comparison is 300 m below the cloud base. The concentration of the cloud droplets is located 90 m above the cloud base. Removing time steps where drizzle was detected decreases the amount of data points available for the analysis. Although very limiting, this filtering is necessary to observe the interaction between aerosols and clouds.
The attenuated backscatter coefficient below the cloud was compared with the corresponding cloud droplet effective radius within the cloud for each time step. The data is divided into bins of LWP. When data is divided into bins of LWP, each of 5 g/m2, the results coincide to the relation that was expected: the increase of the concentration of the aerosol below the cloud corresponds to the decrease of the cloud droplet effective radius. This relation was observed only in the lower values of the LWP. When the LWP exceeds 50 g/m2 there are other processes that take over. Then, there is the suspect that with the higher values of LWP, collisional droplet growth and the entrainment at the top of the cloud influence the relation between aerosols and clouds.

Conclusions and recommendations
- The proposed aerosol-cloud interaction method relies on measurements of automatic-lidar-ceilometer attenuated backscatter, cloud radar reflectivity and microwave radiometer liquid water path. It requires three complementary instruments. All of the required instruments are commercially available.
- The method developed shows encouraging results that link the increase of the concentration of the aerosol below the cloud to the decrease of the cloud droplet effective radius. Relationships are found for clouds with moderate liquid water path (20 < LWP < 50 g/m2).
- To implement the method automatically, a robust target categorization must be available to identify cloud base, drizzle, and aerosol backscatter. The Cloudnet target classification was used, which should be further improved in the future to provide better aerosol classification.


Potential Impact:
ACTRIS provides four types of direct services for the stakeholders: (1) harmonized, reliable, and documented observational data on the chemical and physical state and the processes of the atmosphere, linking surface observations with vertical profiles, total-column observations and cloud processes, (2) training capacity at both data-provision and data-product-usage levels, (3) support for research and application projects conducted at the ACTRIS research facilities, including technological innovation via instrument and service development, new measurement standards and operating procedures, and support to operational activities, and (4) access to facilities.

Many of the ACTRIS observation stations are also belonging to European and international networks, such as the European Monitoring and Evaluation Programme (EMEP - http://www.emep.int a science based and policy driven programme under the UN Convention on Long-range Transboundary Air Pollution), and WMO Global Atmosphere Watch (GAW- http://www.wmo.int/pages/prog/arep/gaw/gaw_home_en.html).

ACTRIS adds an essential capacity in improving observations of the aerosol and trace gases within these networks, contributing to harmonisation of observations, quality assurance, and essential development and implementation of new or improved measurement protocols. ACTRIS plays an essential role in implementing monitoring strategies of these international programs. One excellent example are the new standard operating procedure (SOP) for EC/OC measurements, initiated in EUSAAR, and finalised in ACTRIS. During ACTRIS this SOP is recommended and distributed to the EMEP network, and the SOP is now included as a separate chapter (4.22) in the EMEP manual (http://www.nilu.no/projects/ccc/manual/index.html) as the recommended methodology for all EMEP parties. Recently the CEN WG35 decided that this protocol is the European standard method for the analysis of OC&EC.

Regarding knowledge creation and dissemination, we consider that in the last 10 years, ACTRIS (and the EU-I3 projects EUSAAR, EARLINET and CLOUDNET) has resulted in approximately 1000 scientific papers, 50 books and more than 500 research contracts in the 21 participating countries.


All WPs are contributing to the impact of ACTRIS.


In WP2 it has to be considered both scientific and societal impact. The quality-assured vertical profiles of aerosol parameters (extinction and backscatter coefficients, lidar ratio, Ångström exponents, linear particle depolarization ratio) provided by the WP2 infrastructure are of immediate use by climate modellers who can include this information to improve radiative transfer models assessing the impact of aerosols on the Earth radiative balance. The 4-D information on aerosol distribution (space in three dimensions, and time, thanks to the distributed infrastructure operating in a coordinated way) is of great interest as well to assess the performance of mesoscale transport, chemical and air quality models and to provide feedback for their improvement. It also provides information on trends, which can be used by climate scientist. The activities of WP2 have also had an impact on the ceilometer networks being deployed by many national weather services. WP2 has fostered the development of ceilometer calibration techniques through measurements coincident with those of an advanced lidar, enhancing the ceilometer network performance to validate chemistry transport models and forecast air quality status. WP2 has also developed methodologies for validation of satellite products (in particular from space borne lidars), whose potential impact is very important in view of forthcoming satellite missions involving lidar atmospheric sounding (e.g. ADM-Aeolus, EarthCARE…).
WP2 societal impact is very directly linked to the nature of the topics in which it has scientific impact. For instance, impact on climate studies has an effect on society through change mitigation and adaption policies that may be adopted by governments. Improved transport and air-quality models have a direct impact in population and living being health, with the associated economic impact. A non-negligible societal influence has occurred through the dissemination of knowledge and training of young scientists who will take the lead in scientific progress in the future. In this respect, the backbone of WP2 has been the exchange of expertise tasks, which, through the associated workshops, has enabled a forum in which young scientists can freely exchange with more experienced ones and get used to present results in front of an expert audience, thus honing their research and outreach skills. The impact on training has been enhanced by the coincidence in time with the Initial Training for Atmospheric Remote Sensing (ITaRS) Marie Curie Initial Training Network, in which many participants in ACTRIS WP2 are involved. WP2 has also an impact on technology transfer to the industry, in particular through the SMEs participating in it as associated partners.
ACTRIS WP2 has produced an important number of publications in high-impact-factor peer-reviewed journals and has been present in the major conferences in its topics. An important milestone in result dissemination has been the publication of the EARLINET database with doi number in the Climate and Environmental Retrieval and Archive (CERA) catalogue and archive (http://www.dkrz.de/daten-en/cera). From the methodological point of view, a special issue on EARLINET is underway in EGU’s Atmospheric Measurement Techniques (EARLINET, the European Aerosol Research Lidar Network, Editors: G. Pappalardo, A. Ansmann, R. Ferrare, and N. Sugimoto, http://www.atmos-meas-tech.net/special_issue70.html).


The quality assurance and control activities set in place by ACTRIS WP3 have a huge impact on the quality of the data submitted by European stations to the world date center of WMO-GAW (WDCA). ACTRIS led to a significant growth of the WDCA with quality-assured data, which is largely used by scientific groups in many countries and international institutions such as the WMO. This data are comparable and suitable for the use as model inputs of for model validation as well for decisions on the political level.
One important impact is the adoption of ACTRIS methods in the European standardization (OC&EC, particle counting and sizing). ACTRIS is involved in two working groups of the Centre for European Normalization (CEN). CEN/TC 264/WG 32 decided already on the standardization for measurements of particle number concentration. Presently, the working group drafts a standardization for particle number size distribution measurements using mobility particle size spectrometer, which I based on ACTRIS recommendations. The ad hoc working group of the CEN, who got the mandate from the European Commission to develop a European standard for the measurement of organic and elemental carbon in PM2.5 also chose EUSAAR-2 as the future standard protocol.
Developments of standardized measurement protocols of aerosol instruments in WP3 (ion spectrometer, mobility size spectrometer, integrating nephelometer, absorption photometer, OC/EC analyzer) had also an impact on European SMEs marketing such instrumentation. They have the possibility adapt existing instruments to the new EU standards, and can possibly increase their competitiveness due to the ACTRIS standardizations.


Although at the start of the ACTRIS infrastructure project European VOC and NOx measurements were reported to EMEP and GAW, only a basic quality assurance was included. Within ACTRIS WP4, the European reactive gases measurement community gained the possibility to considerably progress the state-of-the art of the coordination of the VOC and NOx measurements and their quality assurance as well as their reporting.
During the first year of ACTRIS it was decided to tighten the WMO data quality objectives (DQOs) and test their practicality within two pan-European round-robin exercises for NOx and VOC (Hörger et al., AMTD, 2014), respectively. Results were reassuring that these new DQOs were accessible by the most experienced stations. ACTRIS representatives were invited to present the improved DQOs to the GAW community at the WMO/GAW 5th Expert Workshop on VOC (October 2015, Daejong, South Korea). Subsequently, the new DQOs were adopted by WMO.
For less experienced laboratories a learning process was initiated during the course of ACTRIS. Furthermore, a data submission procedure including workshops on data quality assurance and quality control (QA/QC) was implemented in accordance with EBAS (NILU). These measures already show in a more homogenized European VOC and NOx data set submitted to the EBAS data center.
One major achievement of ACTRIS in terms of the measurements of was the upgrading of the WMO Measurement Guidelines for VOC and NOx , which will be reviewed and adopted by WMO in 2016. Here, ACTRIS provided an extremely good environment for both preparing new measurement guidelines and immediately testing their practical application at European representative sites during the round-robin exercises and two side-by-side intercomparisons (supported by TNA of ACTRIS). This whole process was accompanied by the WCC-VOC (KIT), who was a subcontractor of ACTRIS and the new established WCC-NOx (FZ Juelich)
These activities will be - and are strongly recommended to be - continued on initiative of the participating laboratories, in the framework of ACTRIS-2 and on the long term in an ACTRIS ERIC. ACTRIS NA4 reactive gases activities provide the basis for sustainable future NOx and VOC observations in Europe (ACTRIS-2, ACTRIS ERIC and EMEP) and the world (GAW).


The Cloudnet activity in WP5 provides continuous quality controlled observations of cloud and aerosol profiles over nine European locations, compares these observations with the representation of profiles of cloud and aerosol in seven European weather forecast models and has been producing statistics of model performance over the past 15 years.
Weather forecasts of severe weather such as flash-floods and damaging wind storms already provide considerable financial benefit to the European economies. Further improvements in these forecasts would have major benefits through the organization of target mitigation activities based on the short-range forecasts of hazardous weather events. One of the major factors limiting the accuracy of such forecasts is the difficulty in representing clouds, how they evolve and glaciate, and how they produce rainfall. The microphysics of such processes cannot be explicitly represented even though the grid scale of the models is now just 1 or 2 km with as many as 137 levels in the vertical, so the processes leading to cloud and precipitation must be parameterized in terms of bulk variables held at each grid box such as cloud fraction and average cloud water content. Cloudnet analysis show a remarkable improvement in the representation of clouds within weather forecast models up to 2005, but in the last 10 years progress has been disappointing, in spite of considerable investment by national weather services in improving these parameterization schemes.
The recent IPCCC report comments on the unacceptable spread in predictions of global warming and notes that, in spite of massive research investment in climate models, this spread has remained unchanged over the past twenty years. The major cause of this uncertainty is the difficulty in representing clouds. Will a future warmer world have more clouds? If there are more high cold clouds radiating less heat to space, will this exacerbate the global warming, or alternatively, will more low clouds, reflecting more sunlight back to space, attenuate the global warming? Climate models use essentially the same parameterization as forecast models, so improvement in forecast models, which can be evaluated each day are the best prospect for improving our confidence in these forecasts of future climate change. The Cloudnet analysis of continuous high resolution (30/60m in height, every 30seconds) vertical profiles of clouds has the advantage over satellite radars, such the CloudSat radar which has very sparse sampling only at a fixed time of day.
The impact of the ‘Cloudnet’ analysis of the performance of weather forecast models is demonstrated by the 250 citations of the original ‘Cloudnet’ publication (BAMS, 2007, http:dx.doi.org/10.1175/BAMS-88-6-883) including 49 citations during the past four years of ACTRIS. Close relations with the six forecast centres (ECMWF, UKMO, MeteoFrance, DWD, KNMI, and SMHI) have enabled the flow of near-real-time data to be maintained. The results of improved parameterisation schemes in the models have been discussed at two formal workshops.
The performance of new model parameterization schemes has been a major ACTRIS activity. The major shortcomings identified in the BAMS article remain: namely a) all models have about half the observed amount of mid-level (3-7 km) clouds, b) all models have great difficulty producing overcast skies, that is to say filling a grid box with 100% cloud, and c) all models continually convert too much cloud water into light drizzle. Examples of new models schemes that have been introduced to overcome these problems are: a) slowing down the glaciation rate of mid-level clouds so they are more persistent (ECMWF), b) using the level of turbulence to broaden the prescribed spread of relative humidity within the grid box to give more realistic cloud and formation (MeteoFrance), and c) stochastic schemes to vary the auto-conversion of cloud water into precipitation (UKMO and DWD). Cloudnet analysis shows that these updates have improved the model climatology but has not yet resulted in a significant improvement in model skill.


WP-6 has made a major contribution to long-term continuity of ACTRIS observations as part of the European research infrastructures. It has successfully provided the ACTRSI Roadmap to European ACTRIS community, coordinated the ACTRIS-ESFRI proposal (decision pending) and ACTRIS-Horizon2020-proposal (positive decision). During the ACTRIS-I3 WP-6 has provided the conceptual design of ACTRIS core station including data products. Also active dialogue with the end-user communities has made possible to indentify the best possible data products and has also have good visibility for the research work and research infrastructures provided by the ACTRIS community.


Scientific and socioeconomic impact resulting directly from the TNAs are reported below.

The impact of the TNA activities at CIAO (WP7) can be quantified through the results already achieved and described in the 4.1.3 section. They have an important potential socio-economic impact since they are related to the advancement on the knowledge of the following aspects:
1. dust and volcanic outbreaks as a natural hazards for aviation;
2. assessment of the performances of low cost commercial instrument for monitoring air quality, weather and climate;
3. improvement of our capability to monitor air quality and hazards through the assessment of the performance of automatic commercial instruments.
The main dissemination activities are represented by the number of talk and posters presented at meeting and conferences, by the already published paper (Madonna et al., 2015 ATMD), and those in preparation (Mona et al., 2015, Nickovic et al., 2015).

Multiple impacts of trans-national access to the SIRTA (WP8) observatory have been established
- lasting collaborations between researchers from IPSL and international research teams
- a national initiative developed into an international collaboration
- PhD students training and access to data for their research
- Better international visibility of the observatory
- Improved support for SIRTA by national stakeholders to help improve the quality of transnational access.

The impact of TNA activites at MAIDO (WP9) is mainly related to the specificity of the site. The Maïdo observatory is in fact, one of very few multi-instrumented stations in the Southern hemisphere,
Highly accurate vertical profiles measurements of meteorological parameters, ozone, aerosols and water vapour provided by lidars and by night- and day-time radiosoundings in the frameworks of ACTRIS activities and linked to NDACC and GRUAN (GCOS Reference Upper Air Network) have promoted relevant research studies on the composition and on the dynamics of the tropical UTLS (upper troposphere and lower stratosphere) in the Southern hemisphere.

Within ACTRIS, the TNA at SMR (WP10) activities were linked to large European research projects (PEGASOS) or US Department of Energy funded “BAECC”, (Petäjä et al. 2015). Pooling of resourced maximized the scientific outcomes.
As an example, during BAECC, for the first time, the physical and chemical characterization of aerosol particles at the surface was conducted simultaneously with comprehensive cloud and precipitation observations. This was enabled by combining the state-of-the-art capabilities of both the SMEAR-II research station at Hyytiälä, Finland and the AMF2, a mobile research facility, which was brought to Hyytiälä by the ARM program of the U.S. Department of Energy. This facilitated good opportunities to benefit from NASA Global Precipitation Measurement (GPM) mission ground-validation in surface particle size distribution and water equivalent rate gauges while European Commission via ACTRIS TransNational Access provided resources for gap-filling aerosol physical and chemical measurements as well as cloud observations.

The TNA possibility to CESAR Observatory (WP11) has mainly attracted young scientists. It served as a great opportunity for training in the use of advanced instrumentation, improving them as well as the organization of campaigns. It also offered these early stage researchers the opportunity to build their international network. A good example was the ACCEPT campaign of Autumn 2014, in which scientists of the European Marie-Curie trainings network ITARS joined to enhance their scientific skills and deepen insights in clouds and radiation. The TNA activities have sustained the position of the station in the scientific landscape.

The results of the TNA activity at JFJ (WP12) have and will further be communicated to the research community and the public via conference presentations, peer-reviewed publications (see reference list for current status) and media contributions (news articles etc.). There were several media contributions about the TNA activities at the Jungfraujoch, most of them related to the CLACE (Cloud and Aerosol Characterization Experiment) activities, e.g. Swiss regional TV Telebärn, http://www.telebaern.tv/130117-skiextra.html Austrian television, http://www.servustv.com/cs/Satellite/Article/Faszination-Heimat-011259518433310 Swiss Newspapers (e.g. http://www.nzz.ch/wissen/wissenschaft/die-mikrophysik-der-wolken-1.17446847) and other online media for a wider public: http://www.eenews.net/public/Greenwire/2012/11/13/1.

TNA a Mace Head (WP13) brought together a range of scientists and different techniques to advance our understanding and to provide training to young scientists in the marine environment. In terms of new developments at the facility, TNA helped to establish Mace Head as a new facility for ground based remote sensing of cloud microphysics and aerosol profiling using lidar and radar. The synergetic cloud physics retrieval was validated through comparison with in-situ airborne measurements, and Doppler radar and lidar were used to characterise the evolution of turbulent structure in a cloud-topped boundary layer.

TNA at AMO (WP14) supported two PhD studentships and providing technology transfer to enable ammonia measurements in a laboratory study (BOKU, Vienna) and for fluxes in the field (Univ. Politecnica, Madrid). It provided instrument intercomparisons for NOy compounds and O3 flux sensors which provided information that will support the harmonisation of measurement approaches and guide the development / implementation of the next generation measurement technology. Through the TNA at AMO ACTRIS investigated the contribution of organic N compounds, not normally considered, to gas phase NOy burden and the wet deposition budget. The results indicate that organic N makes a significant contribution to N deposition and needs to be included in the assessment of atmospheric N loads to N sensitive vegetation to obtain a more realistic assessment of critical loads exceedances, which will underpin emission regulations within the EU and UNECE frameworks.

All the 6 funded projects as TNA at FKL (WP15) have important potential impact and wider societal implications as they are linked to air pollution, climate and climatic change.
For instance iron and phosphorus are important nutrients for the marine ecosystems. A major source of iron and phosphorus in the open ocean is from atmospheric depositions. In order to evaluate the impact of atmospheric depositions of iron and phosphorus to the ocean ecosystems and thus the climate, global models need to be able to estimate the flux of bioavailable iron and phosphorus from the atmosphere to the ocean. Therefore, it is essential to know what controls the solubility of these elements, which are poorly understood.
In addition information emanating from aerosol characterization is in the forefront of scientific interest as a) it improves the large uncertainty in radiative forcing estimates induced by aerosols/clouds (IPCC 2013), b) it is required to be taken into account in atmospheric corrections (e.g. radiative transfer), c) it is needed in the validation of model simulations. Towards this direction the projects FAME-2011, ADAMA and VAMOS-UAV provided information regarding organic aerosol formation, vertical profile of chemical species and aerosol/cloud interaction.

Results of the TNA activities at HPB (WP16) have meanwhile been presented at various meetings, e.g. EGU annual meeting, ACCENT, EMEP-TFMM, GAW-VOC Expert Group and SAG-RG, VDI Expert Meeting “Atmospheric Chemistry”, IGAC Natal meeting. The NOx and the OVOC intercomparison results including the TNA projects are currently further analysed and will be published in peer reviewed journals. Overall, this will aid confidence in the quality of European long-term VOC and NOx measurements. Results of the TNA projects have been used in the development of ACTRIS Standard Operating Procedures (SOPs) (NA4) for the analysis of VOC and NOx. These provide guidelines for all VOC and NOx stations, are the basis for GAW MGs, and are considered a major component of sustainable, high quality ACTRIS VOC/NOx observation networks. These will enable better verification of abatement strategies of the European Union, like Clean Air for Europe (CAFE) and thus support better air quality and better health in Europe.

The TNA users of RADO (WP17) have been instructed about specific lidar requirements and synergistic approach to retrieve aerosols properties. RADO builds new partnerships and helps new groups to join the networks; to understand and fulfil requirements; to become active as data providers and data users improving the quantity and the quality of atmospheric data from East Europe.
There are envisaged future common collaborations, projects and campaigns with ACTRIS TNA users.

The main impacts of TNA activities at AERONET-Europe (WP18) are:
(i) “integration” through multi-continental integration of research communities in Europe, Africa and Asia (eg, LIDAR, sun-photometers communities);
(ii) “strategic capacity buildings” by creating and maintaining a complementary AERONET system/network in Europe (European self-sufficiency for calibration and operational monitoring), therefore enabling growth of the European network since AERONET-NASA no more willing to allow new sites in Europe, by potentially offering services not only to single user but to network (possibly collocated with other instrumentation), and by providing the unique alternative solution for several countries non-allowed to officially collaborate with the USA;
(iii) “data quality” by reducing calibration time and increasing the observation period and data quality level and disseminating the best practices;
(iv) “innovation” with the unique existing expertize for all CIMEL photometers (Polar, Lunar and “Triple” version) and by contributing to hardware and software development through close partnerships with SMEs, for improving existing technologies (e.g. Lunar photometry proposed in ACTRIS-2), for developing new technologies combining passive/active systems for static and mobile observation and, finally, for developing new added-value processing algorithms requested by these technologies (eg. JRA1).


The ACTRIS Data Centre (WP19) contributes largely to the capacity building and distribution of expertise and know-how as a part of the implementation of new methods and submission of data. At the last ACTRIS Data training workshop (October 2014), there was a particular focus on EC/OC, and providing training of EMEP and GAW data submitters on the new data formats. Experience at the ACTRIS data centre clearly shows that involvement of GAW data submitters at the ACTRIS training courses increase the reporting and quality of data, also from sites outside Europe and lower thresholds to consult across projects/programs.
The open data policy of ACTRIS means positive impacts for the research community (inside and outside ACTRIS) but also for other types of users. ACTRIS data through its observation programmes are made available, understandable and discoverable for all types of users, including industrial partners. Affected by these efforts are for example climate, air quality and water management SMEs instrument technology, consultancies (e.g. wind solar energy). The digital monitoring of the distribution of ACTRIS data from the data centre show that there are more than 2000 unique users, distributed world-wide from almost 70 countries. A detailed analysis of the use of aerosol and trace gas near surface data show that these data are used by 1900 different users, distributed on 65 countries, and also international institution like the EU JRC and WMO are identified users. Most users are located in US (15%), with Norway and Germany as the second and third, respectively. Most of the files download are performed in Norway (18%), mostly due to the regular use of ACTRIS data within MACC (e.g. http://www.gmes-atmosphere.eu/services/aqac/global_verification/validation_reports/ and http://www.gmes-atmosphere.eu/services/aqac/global_verification/#aerosols) which is routed through the Norwegian partner Met.No. France and US are the next user countries, downloading 8% and 7% of the total near surface data volume during ACTRIS.


Instrument synergy is the basis for the implementation of ACTRIS supersites. Through the integration of active and passive remote-sensing capabilities for advanced four-dimensional aerosol observations, WP20 contributed to the further development of a sustainable European research infrastructure for aerosols, clouds, and trace-gas observations.
The Joint Research Activity provides tools to derive volume and mass concentration profiles of particulate matter in the atmosphere and to distinguish between pollution, smoke, dust, oceanic, and volcanic aerosols. These products are in particular useful for model validation and can therefore contribute to an improved forecast of air quality over Europe. Several dust transport models (BSC-DREAM8b v2, NMMB/BSC-Dust, DREAMABOL, DREAM8-NMME-MACC) have been already evaluated against the combined EARLINET/AERONET products. First attempts were also made to validate forecast products of other regional transport and air-quality models. These activities will be increased through the closer collaboration with the modelling community in ACTRIS-2.
The identification and quantification of different aerosol types of natural and anthropogenic origin is also of great interest in the context of satellite validation and global aerosol and radiation modelling. Microphysical particle properties are essential for the calculation of the direct aerosol radiative forcing. Combined ground-based and spaceborne observations will serve for a better understanding of global aerosol effects. By applying common retrieval schemes such as GRASP (Generalized Retrieval of Aerosol and Surface Properties, Dubovik et al., 2014), it will be possible to provide common data products from ground and space. GRASP is a generalized algorithm which applies the same concepts as the WP20 GARRLIC algorithm and is able to process combined observations from space. Therefore, a better integration of ground-based and spaceborne observations is expected in the future, e.g. within the Copernicus programme.
Combined data products from lidar and sunphotometer observations have already been used in different fields of atmospheric research, e.g. to investigate the hygroscopic growth of particles, aerosol mixing states and aerosol-cloud interactions. Several peer-reviewed publications resulted from these activities. With the further distribution of the newly developed measurement and retrieval methods to more ACTRIS stations, and further to the global networks of AERONET and GALION, a continous growth of applications and research results is anticipated.


The activity about ACSM in WP21 mobilized enormous additional resources, as many groups that were no ACTRIS partners joined this activity of continuous aerosol chemistry measurements at their sites with their instruments. As a result, there is today a dataset that covers far more than just the 6 partner stations from ACTRIS. Moreover, many additional groups participated in the ACSM intercomparison exercise and in the development of best practice procedures. In this way, the developed methods have already achieved a high degree of consensus. At the same time, Europe is today perceived as the leader in long-term aerosol chemistry measurements with ACSMs, and the Best practice document for ACSMs (http://www.psi.ch/acsm-stations/acsm-best-practice) is used by ACSM users worldwide. It is also planned to feed this expertise into a document of the Scientific Advisory Group (SAG) for Aerosols of the Global Atmosphere Watch (GAW) programme of the World Meteorological Organization.
As a result, the ACTRIS community has provided a large contribution towards closing the long-standing need for more comprehensive aerosol chemistry measurements. These data will be an invaluable help in providing better aerosol source apportionment data, and, in this way providing the basis towards decisions aiming at improvement of air quality worldwide.
On the other side, the mass closure for gaseous and particulate compounds in the atmosphere assesses the mass contributions of both classes at different sites, ranging from highly-polluted urban to remote environments. The mass closure provides important information not only on the actual mass in different environments but also on the interface between organic particles and the gaseous precursors. In this way, for example, formation processes of secondary organic particles can be studied. In this respect the TOOC (Total Observed Organic Carbon) was proposed as a novel concept by Heald et al. (Atmos. Chem. Phys., 8, 2007-2025, 2008), who also provided first data from different sites in the US. Here all measured gaseous and particulate species are summed together and are compared at the different sites. In ACTRIS this concept was used for the first time in Europe. Gaseous compounds were dominant, a fact in line with comparable studies in the US.
Imminently important in this respect is the possibility of measuring as many single species as possible. Here the Task 21.2 could prove to be very important for the further development of mass closure techniques in Europe as it could provide a more straightforward measurement method for the analysis of oxidised VOCs (OVOCs). OVOCs contribute considerably to the group of gaseous compounds in the atmosphere. However, the measurement capabilities for OVOCs are limited. Proton transfer-mass spectrometry (PTR-MS) has become popular within the recent years. The development of gas chromatography-based methods for the OVOC measurements is considered vital, as such methods are more affordable and can be operated by well trained technicians. Results from an OVOC measurement intercomparison performed within ACTRIS show promising results and thus provide the incentive of using these measurements more widely in different European environments which will be built on in ACTRIS-2.


The methodology developed in WP22 is applied to different cloud profiling observatories of the ACTRIS network. Depending on the availability of instruments dedicated methods can be used, e.g the determination of cloud properties with a multiple field of view lidar system, or using the synergy of radar and lidar for the same purpose. The methodology is based on the CLOUDNET classification scheme and its corresponding data formats, enabling a harmonized and coordinated implementation as number of cloud profiling stations increases. As a result, the capacity of ACTRIS to measure the interaction of aerosols and clouds has been increased and, in view of the continuing development of affordable cloud radars, will continue to do so.


List of Websites:
Project website address: www.actris.eu

Project Coordinator:
Dr. Gelsomina PAPPALARDO, Consiglio Nazionale Delle Ricerche (CNR)
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E-mail: [e-mail]

Project Co-cordinator:
Dr. Paolo Laj Centre National de la Recherche Scientifique (CNRS)
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