WP3: Near-surface observations of aerosols, clouds and trace gases

WP3 Objectives

The overall objective of the activity NA3 is to consolidate and optimize the European capabilities to observe near-surface-based climate and air quality relevant properties of aerosol particles, cloud droplets as well as trace gases concentrations in the troposphere from ground-based stations.ACTRIS-NA3 focuses on improving harmonization of observation methodologies for such variables not yet covered by operational networks. Enhancing provision and dissemination of surface-based high-quality measurements respond to a strong demand of a wide user community. The specific objectives are:
•    To maintain and consolidate provision of high quality data for the variables addressed by ACTRIS in order to assure the quality and stability of the network composed of more than 40 ACTRIS labelled stations around Europe (Task 3.1).
•    To establish new standardized methodologies and procedures for high quality measurements of relevant gaseous, cloud and aerosol variables, when necessary and ensure their implementation (Task 3.2).
•    To implement on- and off-site procedures to further improve data quality and achieve timely identification of instrument malfunctions (Task 3.3).
To exchange expertise and provide scientific and technical support to station operators including new users and dissemination outside the ACTRIS consortium (Task 3.4).

Description of work

Task 3.1: Improvement of instrumentation, standardization and quality assessment of essential climate and air quality variables (EMPA + all NA3 partners)

Regular control procedures were implemented in ACTRIS for harmonization of measurement procedures, quality control and data submission for a specific set of variables relevant to air quality and climate studies. These procedures included regular control exercises through round-robin tests and inter-calibration campaigns and ensured that measurements of in-situ chemical, physical and optical aerosol properties, Nitrogen Oxides (NOx) and Volatile Organic Carbon (VOC) concentrations were performed according to common standard procedures to guarantee traceable high quality. This successful work will be further developed in Task 1 of ACTRIS-2 with the aims to increase the amount and quality of delivered data, to control implementation of existing Standard Operation Procedures (SOPs) and to eventually propose revisions. This will be achieved via inter-laboratory comparison exercises (round-robin), use of ACTRIS TNA (WP8) or external calibration facilities, travelling standards or target gases and calibration campaigns, according to procedures implemented during ACTRIS.  ACTRIS-2 will maintain and further optimize the procedures when necessary. In addition to core variables controlled in ACTRIS (Organic/Elemental carbon – OC/EC-, number and number size distribution of particles, absorption and scattering coefficient of particles, low-level NOx, specific VOCs and specific organic tracers), ACTRIS-2 will implement control procedures for Cloud Condensation Nuclei, new biogenic precursors and oxygenated VOC (OVOCs), additional oxygenated reactive nitrogen (NOy) components, and one additional organic tracer for which SOPs were recently agreed upon in ACTRIS.  The frequency of QA/QC activities follows ACTRIS implementation plan and covers at least one exercise in two different years of the project for each considered variable.
Whenever necessary, inter-calibration campaigns will benefit from and complete ACTRIS experience for specifically targeting identified variables (campaign in the summer months with higher biogenic precursors and OVOC levels). Similarly, inter-laboratory comparison (ILC) studies will be also performed for selected organic aerosol (OA) tracers used for OA source apportionment. The ILC will use both synthetic standards and ambient air test samples to support the establishment of SOPs for variables not already addressed by ACTRIS, such as tracers for primary and secondary OA from biogenic sources, as well as traffic OA, and to determine the quality performance of the participating laboratories.
NA3 strongly relies on ACTRIS calibration facilities. For OC, EC and physical and optical aerosol variables, technical parts of the inter-comparison exercise (e.g. the pure calibration, intercomparison and hands-on training activities) will be performed at World Calibration Centre for Aerosol Physics (WCCAP, WP8) and European Laboratory for Air Pollution (ERLAP, WP8) facilities whereas decisions about data QA strategy, recommendation to users and standardization issues will be addressed in NA3.

Task 3.2: Implementation of new data products and optimization of the processing chain (TROPOS+ all NA3 partners)

The aim of this task is to establish standardizations for high quality measurements for new relevant, cloud, aerosol and gas phase variables for which there is a strong request from a large user community. Some of these new variables were the target of previous JRA in ACTRIS. Each of these developments shall include standardization of the products, definition of metadata, definition and implementation of error products, and documentation. Specifically, Task 3.2 will comprise the following sub-tasks:

Task 3.2.1: Development of a measurement standardization and data submission protocol for aerosol particle mass spectroscopy based on Aerosol Chemical Speciation Monitor (ACSM) products (CNRS, PSI)

Previous JRAs have demonstrated the reliability and robustness of the ACSM to monitor in near real-time and on a yearly basis the chemical composition of fine aerosols and sources of organic aerosols over more than 10 European supersites. The aim of this task is to get homogenous quality-controlled ACSM datasets at a European scale and homogenize calibration and data processing and in particular the source apportionment of organic aerosol data. Precision and accuracy of these measurements will be evaluated with various co-located instruments from such as TEOM-FDMS, SMPS, OC-EC Sunset Field analyzer, PILS-IC, filter sampling …).

Task 3.2.2: Development of a measurement standardization and data submission protocol for cloud relevant products (Liquid Water Content (LWC) and droplet effective radius (Re);(CNRS, PSI)

Instruments capable of characterizing clouds properties are diverse in the community. The first aim of this activity is to harmonize the standard operation procedures for the measurement of LWC and Re by the bulk probes (PVM) and evaluate their performances, compared to the other existing probes. We will also provide the recommendations and standard operating procedures to the ACTRIS community and define data format for submitting data through the ACTRIS data portal.

Task 3.2.3: Development of a measurement standardization and a data submission protocol for VOCs based on PTRMS and TOF-MS measurements (CNRS, EMPA)

PTRMS and TOFMS instruments are now used to perform high-time resolution VOC measurements. They are also of great interest when combined to speciated measurements of aerosols (AMS and ACSM). ACTRIS-2will provide the scientific community with standard operating procedures for PTRMS and TOFMS measurements to ensure proper management of interferences, as well as a good quality of blanks and standard gases. Recommendations will be inferred from the intercomparison of OVOC instruments (Task 1) and from the experience gained by PTRMS and TOFMS experts. In a joint effort with the aerosol working group, PTRMS and TOFMS will be implemented during ACSM intercomparison to check whenever organic aerosol sources can be determined based on the synergy between ACSM and PTRMS.

Task 3.2.4: Development of a measurement standardization and data submission protocol for coarse mode particle number size distribution measurements based on aerodynamic and optical particle size spectrometers (TROPOS).

In EUSAAR and ACTRIS standardization protocols have been developed and implemented for particle number size distribution measurements based on mobility particle size spectrometers covering the sub-micrometer particle size range. Since most of the ACTRIS stations use aerodynamic and optical particle size spectrometers for the super-micrometer particle size range, standardization protocols will be developed for these measurements to cover also the optically and microphysically relevant size range of coarse particles.

Task 3.2.5: Development of reference instruments for multi-wavelength absorption measurements (TROPOS).

Since multi-wavelength absorption photometers are more and more used, there is a need to define a laboratory reference method to be able to validate the retrieved multi-wavelength absorption coefficients of such photometers during calibration and intercomparison workshops. Extinction monitors and integrating nephelometer will be the base of the future ACTRIS reference method for the multi-wavelength particle light absorption coefficient.

Task 3.3: Development and implementation of advanced data quality-check tools from station operation to data submission (NILU + all NA3 partners)

The aim of this task is to perform on- and off-site quality assurance studies to further improve data quality and facilitate rapid identification of instrument malfunctions. In this frame, elaborated tools and semi-automated interactive statistical procedures for assessing the quality and consistency of measurement data will be developed and implemented throughout the network of stations. This comprises advanced tools for both on-line/off-line identification of instrument failure/deviations and facilitation of submission procedures. This task will comprise the following sub-tasks (in parenthesis in Italics the sub-task leader(s)):

Task 3.3.1: Development and implementation of advanced on-line QC tools. (NILU, EMPA, DWD, TROPOS, CNRS, JRC)

On-line tools will be developed and distributed to stations operators to ensure more rapid identification of instrumental failures. The probably most sensitive test for hard-to-detect instrument malfunctions is the physical consistency between different instruments (closure). Examples of such tests are check of ratios of trace gas concentrations and comparison of aerosol properties measured directly and calculated from collocated observations of microphysical aerosol properties. Three concrete activities are listed below.
•    Closure studies for total particle number concentration (TROPOS). Up to four transfer Condensation Particle Counters (CPC) will be employed for on-site intercomparisons against mobility particle size spectrometers. Each CPC will travel from station to station and finally quality assured at the calibration centre WCCAP.
•    Closure studies for particle light scattering coefficient (NILU, TROPOS). For stations which operate an integrating nephelometer together with a mobility particle size spectrometer and additionally an optical aerodynamic particle size spectrometer, automatic intercomparisons of the measured(integrating nephelometer) and calculated particle light scattering and backscattering (Mie-model for spherical particles and e.g. a T-Matrix method for spheroidal particles) will be performed to assess a quality assurance of both measurements methods (correct determination of the particle number size distribution of the accumulation and coarse mode range and the calibration of the integrating nephelometer).
•    Mature automatic QA/QC checks for incoming VOC and NOx data. (EMPA, DWD).Checks will include the comparison of monthly means between different sites and ranges of trace gas ratios, both within one station and between different stations. These tools will be developed within task 3.2. This will allow a straightforward preliminary feedback of the data quality, which then will be further elaborated before final submission in task 3.2.

Tools will also be implemented within the in-situ data centre EBAS to the benefits of all users (partners and associated partners). One direct impact of the centralized on-line tool will be to increase the number of stations providing data in near-real-time. This will clearly serve interaction of the infrastructure with models for operational weather prediction in JRA3. This will be achieved by creating demonstrator use cases for near-real-time (NRT) data in collaboration with JRA3, thus increasing the motivation of data submitters to participate in the NRT infrastructure by demonstrating the data’s relevance. Software packages implementing the NRT data submission at station level will be shared to lower the threshold for participation. If considered mature, new instruments and parameters will be added to the NRT infrastructure.
Task 3.3.2:Reactive trace gases consistency checks, using trace gas ratios and chemical concepts (EMPA, DWD, NOA). NOx and VOCs trace gas ratios are an important tool for checking the consistency of trace gas data both at one station between different years and between different stations. This includes consideration of background values, emission ratios, photochemical ageing, NOx-photo-stationary-state. Mature products will be transferred to task 3.1 and partners will be trained and annual workshops well in advance of the actual data submission will be organized to ensure the compliance with QA/QC procedures and intercomparability of the submitted data within ACTRIS-2.

Task 3.3.3: Development and implementation of automatic and interactive sanity and consistency checks for in situ surface-based data submission (NILU)

Despite careful double manual quality assurance by data provider and data centre, some errors in submitted data and metadata are not detected before archiving. Experience shows that many of these errors can be avoided, and thus data quality improved, by adding automatic checks of syntax, metadata consistency, and data boundary / outlier checks on top of manual sanity checks. To this end, the named automatic checks will be implemented for data submitted by FTP to the ACTRIS data centre, together with a feedback mechanism by e-mail. In addition, a website will allow data submitters to perform the same checks interactively on their prospective data submission. This will reduce the turn-around time for feedback to data submitters significantly. In total, this will result in an improved user experience for data submitters as well as better data quality for data users. An expert workshop early in the project will specify the details of the sanity tests.

Task 3.4: Exchange of expertise, support to campaigns and new users (NOA + all NA3 partners)

This task will be the backbone of the networking activity through which the participants (partners and associated partners) share scientific and technical expertise relevant to NA3, discuss outcomes of Tasks 3.1, 3.2 and 3.3 and implementation procedures throughout the research infrastructure. Task 4 provides opportunities to exchange and transfer technical expertise and advice in particular to new users. The task will support the following items:

-    Organization of annual workshops and task-related technical meetings (NOA, CNRS, TROPOS, DWD, EMPA): Annual technical workshops will be organized to discuss progress of the tasks as well as specific topics (such as user requirements, instrument and data analysis optimization, external collaboration, etc.). Workshops will be open to partners and associated partners including SMEs. Next to the workshops, task-related technical meetings will be fostered to facilitate progress of specific developments.
-    Implementation of ACTRIS products and QA procedures within the network and in support of large research EU-projects field campaigns (TROPOS, CNRS, NOA, DWD, EMPA): The increasing use of instruments for physicochemical and optical properties of aerosols and trace gases measurements such as ACSM, PTR-MS etc. in field experiments requires specific support such as consideration of specific sites and platforms (e.g., ships) etc. Respective expertise will be provided to users on request.
-    Support to new stations (TROPOS, CNRS, NOA, DWD, EMPA): NA3 partners will provide guidance and technical support to new stations implementing NA3 relevant instrumentation. As near-surface ACTRIS network for aerosols, trace gases and cloud variables is still growing, new stations must fulfil a large number of requirements to adjust to the networks’ standards.
Documentation, websites, and outreach (NOA, CNR, CNRS, TROPOS, DWD, EMPA): Documentation of meeting results, task-related documentations, standardization protocols, technical descriptions and any information relevant for the users will be made available through publication on the ACTRIS website and via task-related websites and interfaces.