WP Leader: Stefan Reimann


  • To integrate and harmonise trace gas measurements in Europe, with the result of having a sustainable and reliable observation network for highly time-resolved data across Europe. 
  • To implement standardised measurement protocols (SOPs) and common European calibration scales for VOCs and NOxy in support of the European EMEP and global GAW strategy and according to data quality objectives formulated by these initiatives. 
  • To create a protocol for merging the information of ground-based in-situ and remote sensing capacities in order to achieve more comprehensive distributions of VOCs and NOxy in Europe. 
  • To foster the dissemination of the methods and quality assured data to scientific groups related to the analysis and modelling of air pollutants in Europe and to support EC directives relevant for air pollution and the CLRTAP abatement strategies.

Description of work

The term gaseous precursors of secondary air pollutants comprise a wide range of chemical species and reactivities. Precursors (i.e. primary pollutants) are emitted either by anthropogenic or biogenic sources, with the volatile organic compounds (VOCs) and the nitrogen oxides (NOxy) as main groups. Important secondary air pollutants produced from these precursors are ozone (O3), secondary organic aerosols (SOA) and nitrates. Measurement capacities for these primary air pollutants in Europe are widespread but coordination is essentially missing or performed within projects of only limited periods. Most important gaps are (i) the usage of standardized operation procedures, (ii) common calibration standards and scales, (iii) the submission to common data base and (iv) the usage of data for state-of-the-art models. WP4 responds to the demand of the scientific community for reliable monitoring of air pollutants at high time resolution in a standardised way across Europe. This is of interest for the climate and air quality modelling community and political entities (e.g. Directive 2008/50/EC, CLRTAP/EMEP) and the general public. ACTRIS will target the harmonization of on-line, trace level gaseous air pollutant measurements, yield reliable concentration fields and trends in Europe, help to quantify the relative contribution of anthropogenic sources and improve air pollution abatement strategies.

WP4 is divided into 2 main tasks.
- Task NA4.1: Coordination of European VOC measurements
- Task NA4.2: Coordination of European NOxy measurements
For a straightforward organization, tasks NA4.1 and NA 4.2 have identical structures with:
1. sub-task: Development of SOPs within meetings of the European experts in the field.
2. sub-task: Testing best measurement practices in experiments (round-robin/on-site intercomparisons/station
3. sub-task: Link ground-based in-situ measurements with vertical profile information.

 Task 4.1  Coordination of European VOC measurements.
The term VOCs in WP4.1 consists of 3 subgroups:
NMHCs (C2-C9 hydrocarbons), OVOCs (oxidised volatile organic compounds) and terpenoides (biogenic hydrocarbons with a terpene-structure). These 3 groups encompass the most important VOCs both in abundance in the atmosphere and in importance for the formation of secondary air pollutants. Albeit their importance only a very limited number of sites perform VOC measurements on a continuous basis. Most of the sites within Europe take samples twice a week by filling stainless steel canisters and measure NMHCs in central laboratories according to a procedure outlined in the measurement guide by EMEP. For OVOCs and terpenoides (which are equally important but more difficult to measure) only a very restricted number of sites in Europe perform measurements at all. In NA4.1.1 the knowledge of leading experts and sites performing VOC measurements in Europe will be merged during 2 consecutive workshops for the preparation of standard operation procedure (SOPs) and to implement a European network for VOC measurements. The SOPs will be prepared considering the results gathered in NA4.1.2 during round-robin exercises, on-site audits and comparison between the different measurement systems during common campaigns.
An integrative task of the participants is the submission of finally quality assured VOC data (according to the SOPs defined within ACTRIS) to the ACTRIS data centre.
Task 4.1.1
 Development of SOPs for harmonization of VOC-species measurements in Europe (EMPA, DWD, UHEL, NILU, JRC, CNRS)
In workshop-1 (EMPA) the key issues in high quality measurements of VOCs (NMHCs, OVOCs, terpenoids), data quality objectives (DQOs), error assessment, and data processing shall be identified, based on existing knowledge from recent QA projects, e.g. NOMHICE, AMOHA, and ACCENT (all). Furthermore, specific criteria for the data delivery shall be defined. Draft documents for standardised procedures for measurements, calibration, quality assurance, error assessment, and data processing and reporting (SOPs) are prepared (EMPA/DWD/UHEL/NILU and all) taking into consideration previous work from the FP4 European project AMOHA (for NMHCS), activities in the GAW expert group for VOC (GAW report 171) and the EMEP community (NILU). Questionnaires to capture the details of the measurements and during station audits will be prepared by EMPA together with the GAW World Calibration Center for VOCs, WCC-VOC. In workshop-2 (EMPA), the
results from NA4.1.2 will be assessed and will be incorporated into the final standardised operating procedures (SOPs). These are then supplied to serve the scientific community, GAW and EMEP. The workshops will be organised and hosted by EMPA.
Task 4.1.2
 Testing best measurement practices in QA experiments for VOCs (EMPA, DWD, UHEL, NILU, JRC, CNRS and all) 
For the 3 groups of VOCs (NMHCs, OVOCs, terpenoids) specific round-robin exercises will be initiated at the workshop-1, with synthetic standards and real-air reference-gases being sent to all the important scientific groups in Europe having a long-term commitment to those specific VOC measurements. The real air reference gases will be prepared in special stainless steel cylinders and the reference concentrations will be determined by EMPA, WCC-VOC (intended), and DWD. Furthermore, intercomparison measurement campaigns will be organised for NMHC at Jungfraujoch (EMPA), and OVOC at Finokalia (FORTH). In addition, audits at selected sites will be performed by the WCC-VOC (intended).
Data from the round-robin exercise and the comparison campaigns will be analyzed by the respective organising infrastructure, reports are prepared, and the results will be incorporated into the final versions of the SOP, according to good laboratory practice and state-of-the art (EMPA/DWD/NILU).
 Task 4.1.3  Link vertical profile information for VOCs to ground based measurements (BIRA-IASB, DWD, NILU, CSIC)
 The comparison of MAXDOAS and FTIR instruments for a selected set of VOCs with on-line ground based instruments will be assessed during workshops-1 and -2). A document on the achieved results will be prepared by BIRA-IASB and the comparability of the profiles obtained by MAXDOAS/FTIR and the ground based measurements will be assessed.
 Task 4.2  Coordination of European nitrogen oxide (NOxy) measurements
The parameters considered are nitric oxide (NO), nitrogen dioxide (NO2) and their sum (NOx) as well as the sum of reactive oxidized nitrogen compounds (NOy). NO and NO2 significantly impact the chemistry of ozone and the hydroxyl-radical (OH), whereas NOy is related to aerosol nitrate. Therefore, the nitrogen oxides are coupled to oxidant formation, oxidizing capacity, acid rain, aerosol, and climate. Monitoring of these parameters is in accordance with the EMEP measurement strategy for level 2/3 sites (super-sites), the GAW Strategic Plan 2008-2015 (report 172) and the identified needs of observation by ACCENT (Understanding and Quantifying the Atmospheric Nitrogen Cycle, ACCENT report 3.2006).
The NOxy infrastructure in Europe (stations committed to long-term NOxy observations and leading scientists in this field) are brought together in 2 workshops, and in joined activities complying comparisons and station audits, and in preparing documents for dissemination of standardised procedures. These procedures shall follow the recommendations of GAW (GAW-Meeting of the NOxy expert-group at Hohenpeissenberg, 8.-9.10-2009, and the corresponding GAW Report in preparation), i.e. use of chemiluminescence technique (CLD) for NO, and combined with photolytic conversion for NO2. Additionally, CLD shall be used with gold converters for NOy.
Ongoing activities in the GAW community towards the implementation of a global measurement network and central facilities comprising a World Calibration Centre (WCC) and a Central Calibration Laboratory (CCL) shall be supported (GAW-Meeting of NOxy expert-group, see above). An integrative task of the participants is the submission of quality assured NOxy data (according to the SOPs defined within ACTRIS) to the ACTRIS data centre.
 Task 4.2.1 Harmonize NOxy-species measurements in Europe (DWD, NILU, CNRS, NERC, EMPA) 
 During an initial workshop-1 (DWD) the key issues in high quality measurements of NO, NO2 and NOy, data quality objectives (DQOs), QA, error assessment, and data processing shall be identified (DWD, NILU, CNRS, NERC, EMPA and all). Draft documents for standardised procedures for on-line measurements, calibration, quality assurance, error assessment, and data processing and reporting (SOPs) will be prepared making use of ongoing activities in the GAW and EMEP communities. Questionnaires to capture the details of the on-line measurements and for use during station audits will be prepared (DWD).
In a second workshop-2 (DWD), with the results of the measurement questionnaire, station audits, a round robin (Task NA4.2.2) and side-by-side inter-comparison being available, the draft SOPs will be discussed and revised ((DWD, NILU, CNRS, NERC, EMPA and all). Final SOPs will be developed and supplied to serve the scientific community and GAW and EMEP (DWD). The workshops will be organised and hosted by DWD.
 Task 4.2.2 Improvement of quality assurance and dissemination of knowledge (DWD, NILU, CNRS, NERC, EMPA and all) 
 Currently, in GAW no WCC and CCL for NOxy species measurements exist. During the recent GAW NOxy expert workshop (s.a.), an institution to take over the responsibility of a WCC has been recommended.
Furthermore, selected National Metrological Institutes have been recommended to take over the tasks of a CCL. Thus, initial steps have been made but the process of implementing these central facilities will take years and need support (DWD). Accordingly, QA is rather poorly developed in the network and currently depends on initiatives by individual stations and the aforementioned GAW NOxy workshop. This gap is addressed by implementing a QA procedure based on 4 columns (SOP, round robin and inter-comparison, station audit, and training of station staff):
A round robin exercise with certified NO mixtures (ppm and ppb) will be performed by DWD in close cooperation with the WCC-NOxy. Test gas cylinders will be supplied to European NOxy sites and the participants will be asked to quantify them using their own calibration gas. Also, side-by-side intercomparisons in the field will be carried out at Hohenpeissenberg (see also TNA MOHp). The intercomparisons are envisioned to cover the needs of European NOxy-stations and on-line NO, NO2 and NOy measurements. The results of round robin and inter-comparison will be evaluated and disclosed to participants by DWD and WCC-NOxy, and discussed during the second workshop.
Station audits are a central part of QA. The measurement capability of the sites audited for the various NOxy compounds and compliance to standardised procedures (SOPs) defined during the workshops will be characterized. This comprises auditing of the inlet system, the calibration, the measurement procedure and the data evaluation. A common audit questionnaire will be used (see above). Essential is the dissemination of the achieved results on the web portal. These audits will be carried out by the designated WCC (intended). Stations willing to upgrade their measurement techniques for NO, NO2, and NOy will be supported by recommendations on appropriate instruments for the encountered concentration range of ambient air, inlet systems and necessary maintenance by DWD and WCC-NOxy. In cooperation with GAWTEC, a jointly funded activity between the German QA-SAC (UBA-Germany) and the Bavarian State Government, a training program for station managers and technicians is envisioned. This will make use of the established GAWTEC programme and result in well trained personal to follow the newly developed SOPs and thus guarantee the implementation of the high quality, standardised measurements.
In the final workshop-2 the audit results will be discussed and the SOPs are revised with respect to new insights (DWD, NILU, CNRS, NERC, EMPA and all). Concepts for rapid data processing and delivery to data centre are developed and tested. Documents on the sustainability of QA and SOPs achieved will be prepared (DWD).
 Task 4.2.3  Link vertical profile information to ground based measurements for NOxy (BIRA-IASB, DWD, NILU, CSIC)
 The comparison of MAXDOAS and FTIR instruments for a selected set of NOxy with on-line ground-based instruments will be assessed during workshops-1 and -2). A document on the achieved results is prepared by BIRA-IASB and the comparability of the profiles obtained by MAXDOAS/FTIR and the ground based measurements will be assessed.



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