Advanced Chemical process Modelling of aqSOA (ACoMa)

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Organic aerosols (OA) represent an ubiquitous major component of atmospheric aerosols affecting numerous atmospheric processes and environmental issues. The quantitative assessment of, e.g., climate effects remains hampered by a number of factors, including an incomplete understanding of how emitted VOCs contribute to the formation of atmospheric OA. A huge fraction of OA is formed secondarily (secondary organic aerosol (SOA)) in the atmosphere through gas phase chemical processes including subsequent gas-to-particle partitioning (gasSOA) or through aqueous phase chemical processes (aqSOA). However, by means of pure gas phase chemistry approaches, the properties of the ambient SOA cannot be explained. Furthermore, gasSOA approaches tend to underestimate the overall SOA. From several laboratory and field studies, it was concluded that the aqSOA formation might have the same importance than the gasSOA formation. Thus, there is a growing attention on aqueous phase processes contributing to the SOA. But, the chemical aqSOA processing, i.e. secondary formation and aging of aqueous OA, remains poorly understood and considered in current multiphase chemical mechanisms. To further address this scientific issue, further investigations with more detailed multiphase chemistry mechanisms and advanced process models are needed to predict more accurately photochemical processes of organic compounds in the atmospheric aqueous phases.In order to improve the current understanding of the aqSOA processing and their importance for the tropospheric chemistry and its related scientific issues, the present project aims at the development of an advanced aqSOA chemical mechanism and an advanced multiphase model. The model should near-explicitly treat the inorganic/organic chemistry in both the gas phase and aqueous phase including radical and non-radical chemistry of organic compounds. Moreover, the aimed advanced multiphase process model will sufficiently treats complex/salt formation processes and non-ideal solution effects. By means of such an advanced multiphase model the tropospheric chemical aqSOA processing will be investigated in detail by accompanied model studies. The proposed model studies will focus mainly on (i) the identification of the main aqSOA formation pathways, (ii) the importance of radical, non-radical and non-oxidative processes for aqSOA within different environmental regimes and (iii) the importance of interactions of organic compounds with inorganics for their tropospheric resistance time. Overall, by means of the advanced multiphase model framework and the projected model studies, new insights will be provided into aqSOA processing, its importance for the overall particulate OM formation and the link to other important tropospheric chemistry issues such as the tropospheric oxidation capacity.