Bimodal size distributions of various organic acids and fatty acids in the marine atmosphere: Influence of anthropogenic aerosols, Asian dusts, and sea spray off the coast of East Asia

Size-segregated (11 stages) marine aerosol samples were collected off the coast of East Asia during the ACE-Asia campaign in 2001 and were analyzed for homologous series of dicarboxylic acids (C-2-C-12), omega-oxocarboxylic acids (C-2-C-4), and n-fatty acids (C-16-C-30), as well as organic carbon (OC), elemental carbon, and major inorganic ions. Concentrations of OC and major diacids and oxoacids in continental polluted air masses showed predominantly submicron maxima. However, during dusty haze events, supermicron maxima were observed, suggesting a size shift due to the secondary accumulation of these components on dust as well as sea salt particles. Supermicron maxima were also found for palmitic acid (C-16 fatty acid) and other lower-molecular-weight fatty acids (LFAs, C-16-C-19) that are emitted from a microlayer of the ocean surface. In contrast, higher-molecular-weight fatty acids (HFAs, C-20-C-30) were mainly detected in the submicron mode, presumably due to a substantial contribution of biomass burning aerosols. This study demonstrates a high-variability in the size distributions of organic components (i. e., between submicron and supermicron modes) in the coastal regions off East Asia. Such variations in the physical properties of the marine aerosols may be important in relation to their cloud-condensation-nuclei and light extinction activities.