PARAMOUNT (Production of Aerosol paRticle orgAnic Matter in ClOUds: chamber and laboratory studies, mechanisms, modelling and iNTegration)

Chemical processes in clouds have been suggested to contribute substantially to organic aerosol particle mass. Recent evidence from the HCCT-2010 field study and the CUMULUS chamber study suggest that this organic mass production can be substantial and depends on the concentration of available organic precursor compounds in the gas phase. However, considerable uncertainties exist, e.g., with regards to the nature of the resulting aerosol particles which might be metastable and loose at least part of their organic mass (OM) content during the cloud droplet evaporation. Hence, PARAMOUNT is aimed at the investigation of cloud processes which are able to process organic constituents and produce organic aerosol particle mass. The project will focus on the multiphase chemistry of very relevant polyfunctional precursors such as polyfunctional carbonyls and acids. With these precursors, a combination of aqueous-phase laboratory and CESAM chamber studies will be undertaken to examine the multiphase cloud processing. Firstly, aqueous-phase laboratory studies will lay the groundwork with regard to kinetics and mechanisms of the multiphase processing of the mentioned compounds. Then, the suggested CESAM chamber experiments, which are central in PARAMOUNT will focus on studying the organic mass production by the chemical in-cloud processing of these compounds one by one, grouped or with mixtures with all of them. The planned chamber studies will use different seeds and oxidant precursors to examine the organic mass production under different environmental and diurnal conditions. The organic mass increase during the cloud episodes will be investigated. Besides the organic mass formation, the partitioning of organic compounds under cloud conditions should be studied to evaluate possible enrichments of organic carbonyl compounds observed during the cloud field campaign HCCT-2010. The organic aerosol fraction will be analysed on-line by two Aerosol Mass Spectrometer instruments and the processing of the interstitial gas phase and the phase partitioning will be investigated by PTR-MS and the use of a mini CVI (counter virtual impactor) followed by off-line analysis. Finally, the performed CESAM experiments are being modelled with the complex multiphase chemistry mechanism MCM/CAPRAM. The multiphase modelling will be performed to both validate the mechanism and support the interpretation of the chamber experiments. Overall, the project PARAMOUNT will improve the understanding of in-cloud processes and clarifying the role of clouds for atmospheric organic aerosol mass production.

References

Herrmann H., Schaefer T., Tilgner A., Styler S. A., Weller C., Teich M., Otto T. (2015) Tropospheric Aqueous-Phase Chemistry: Kinetics, Mechanisms, and Its Coupling to a Changing Gas Phase. Chemical Reviews 115 (10), 4259-4334, doi: 10.1021/cr500447k.

Schaefer T., van Pinxteren D., Herrmann H. (2015) Multiphase Chemistry of Glyoxal: Revised Kinetics of the Alkyl Radical Reaction with Molecular Oxygen and the Reaction of Glyoxal with OH, NO3, and SO4– in Aqueous Solution. Environmental Science & Technology 49 (1), 343-350, doi: 10.1021/es505860s.