Secondary Organic Aerosol Formation over Coastal Ocean: Inferences from Atmospheric Water-Soluble Low Molecular Weight Organic Compounds

摘要

A lack of consensus on the distributions and formation pathways of secondary organic aerosols (SOA) over oceanic regions downwind of pollution sources limits our ability to assess their climate impact globally. As a case study, we report here on water-soluble SOA components such as dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in the continental outflows from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA) to the Bay of Bengal. Oxalic acid (C_2) is the dominant species followed by succinic (C_4) and glyoxylic acids (ωC_2) in the outflow. Nonsea-salt SO_4~(2-) also dominates (~70%) total water-soluble inorganic constituents and correlates well with aerosol liquid water content (LWC) and C_2, indicating their production through aqueous phase photochemical reactions. Furthermore, mass ratios of dicarboxylic acids (C_2/C_4, C_2/ωC_2), and their relative abundances in water-soluble organic carbon and total organic carbon are quite similar between the two continental (IGP and SEA) outflows, indicating the formation of SOA through aqueous phase photochemical reactions in LWC-enriched aerosols, largely controlled by anthropogenic SO_4~(2-).