JRA2: Comprehensive gas phase and aerosol chemistry

WP Leader: Urs Baltensperger

Objectives

  • To enhance the capabilities of long-term measurements of aerosol chemistry at network stations 
  • To develop optimized and standardized techniques for the measurement of oxygenated volatile organic compounds (OVOC)
  • To perform mass closure experiments by combined measurements of organic carbon compounds in the gas and particle phases

Description of work

 

 Task 21.1

 Aerosol Chemistry (PSI, TUD, FORTH, IFT, NUIG, UHEL)

The Aerosol Chemical Speciation Monitor (ACSM) 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, by also providing composition information for particulate ammonium, nitrate, sulfate, 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.
Within ACTRIS the performance and suitability of this instrument shall be assessed at the following sites: Mace Head, Cabauw, Melpitz, Hyytiälä, Finokalia, and Jungfraujoch. For this purpose the six involved partners will purchase one ACSM each with internal funds (i.e., with no costs charged to ACTRIS). Particulate ammonium, nitrate, sulfate, chloride, and organic mass concentration will be measured, wherever possible, for a full year.
The data will be compared with data obtained by other techniques at the same site (either by the MARGA technique (Monitoring instrument for AeRosols and Gases), an aerosol mass spectrometer, or off-line filter samples. The ACSM measurements will be planned in coordination with the mass closure experiments (Task 3).
Existing multivariate mathematical techniques will be applied to the data in order to check if these can also be applied successfully to the ACSM data at these highly diverse sites.

 

 

 Task 21.2

Development of OVOC instrumentation for mass-closure experiments (EMPA, DWD)

OVOCs are difficult to measure on-line. Although PTR-MS have improved the possibility for the measurement of OVOCs fundamentally, the definite determination of certain compounds is still only possible with a certain degree of ambiguity. OVOC are not straightforward to measure by GC techniques either, though it is accepted that GC systems are capable of high quality measurements of the light OVOC comprising C1-C4 alcohols, and C1-C4 carbonyls. Problems arise from the fact that OVOC are polar compounds and highly sticky to surfaces of the sampling system, water soluble and thus prone to artefact losses in water traps, and they form in oxidation of other VOC in reactions with ozone and other oxidants. It is well known that the problematic part is the gas sampling and sample preconditioning part (tubing, watertrap, enrichment, thermal desorption)
and not the GC separation and detector system. There exist OVOC systems at various installations (EMPA, DWD, ...) with individual advantages and disadvantages, however, no standardization and joint optimization of these instruments has been developed. A standardized OVOC technique will be developed based on on-line GC-technique with water-trap and enrichment (cooled adsorbent trap), followed by GC-capillary column separation and detection by FID or MS. The focus will be on a standardized sampling and enrichment module, which can then be attached to any GC-FID system on the market. Two of these standardized sampling modules will be tested against PTRMS as a reference system, with the goal to demonstrate routine operation of these OVOC systems, and achieve high quality results that are appropriate for mass-closure experiments.

 

 Task 21.3

Performance of mass closure at different sites (EMPA, DWD, PSI, TUD, FORTH, IFT, NUIG, UHEL)

A new approach for holistic consideration of the total organic carbon (TOC) budget will be tested at 2 sites that are equipped with an ACSM (see Task 1) during campaigns in summer and winter. Similar budget approaches are routinely used for nitrogen oxides and sulfur in the atmosphere, and rapidly improving measurement techniques are beginning to make this possible for organic carbon. The organic carbon budget includes a large suite of compounds, with many that are likely to contribute have hardly been observed under ambient conditions. Therefore, the combined analysis of gaseous compounds, which play an important role in the chemistry of the troposphere, and particles which are a climate forcing agent is an important issue.
This mass closure of atmospheric organic carbon will be achieved by bringing together state-of the art equipment for both gaseous and particulate organic substances (GC-FID/GC-MS/PTR-MS/ACSM) and others depending on the site's characteristics.

 
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