Seminar

Abstract

The role of organic aerosols in the climate system has been recognized over several decades and much progress has been made in the characterization of their sources, transformation and radiative impacts. Globally, about 50% of the total organic aerosol mass is formed from precursor compounds in the atmosphere (secondary organic aerosol, SOA) and not directly emitted (primary organic aerosols, POA).

Current models assume formation of SOA compounds and vapor-pressure driven partitioning to an organic aerosol phase (gasSOA). While such model approaches often lead to a reasonable agreement in SOA mass prediction, I will show discrepancies in predictions of SOA oxidation state, molecular mass distribution, and dependence on relative humidity that suggest additional SOA sources and aging processes may be important. The formation of SOA mass in cloud and aerosol water (aqSOA) is not considered in these SOA models even though oxygenated organics in the atmosphere are likely to dissolve and get further chemically processed in an aqueous phase rather than to absorb into an organic phase.

The talk will summarize direct evidence from field observations and laboratory studies that organic aerosol mass is formed in cloud and aerosol water, which might provide an efficient and unique chemical route to formation of oligomers and other high-molecular-weight compounds that comprise a significant fraction of the organic aerosol. Current approaches will be discussed how to implement aqSOA formation in process models based on available laboratory data, and suggestions for improvements of models on a larger scale will be made.