Dicarboxylic acids, oxoacids, benzoic acid, alpha-dicarbonyls, WSOC, OC, and ions in spring aerosols from Okinawa Island in the western North Pacific Rim: size distributions and formation processes
Résumé
Size-segregated aerosols (nine stages from < aEuro-0.43 to > aEuro-11.3aEuro-A mu m in diameter) were collected at Cape Hedo, Okinawa, in spring 2008 and analyzed for water-soluble diacids (C-2-C-12), omega-oxoacids (omega C-2-omega C-9), pyruvic acid, benzoic acid, and alpha-dicarbonyls (C-2-C-3) as well as water-soluble organic carbon (WSOC), organic carbon (OC), and major ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-, and MSA(-)). In all the size-segregated aerosols, oxalic acid (C-2) was found to be the most abundant species, followed by malonic and succinic acids, whereas glyoxylic acid (omega C-2) was the dominant oxoacid and glyoxal (Gly) was more abundant than methylglyoxal. Diacids (C-2-C-5), omega C-2, and Gly as well as WSOC and OC peaked at fine mode (0.65-1.1aEuro-A mu m) whereas azelaic (C-9) and 9-oxononanoic (omega C-9) acids peaked at coarse mode (3.3-4.7aEuro-A mu m). Sulfate and ammonium were enriched in fine mode, whereas sodium and chloride were in coarse mode. Strong correlations of C-2-C-5 diacids, omega C-2 and Gly with sulfate were observed in fine mode (r = aEuro-0.86-0.99), indicating a commonality in their secondary formation. Their significant correlations with liquid water content in fine mode (r = aEuro-0.82-0.95) further suggest an importance of the aqueous-phase production in Okinawa aerosols. They may also have been directly emitted from biomass burning in fine mode as supported by strong correlations with potassium (r = aEuro-0.85-0.96), which is a tracer of biomass burning. Bimodal size distributions of longer-chain diacid (C-9) and oxoacid (omega C-9) with a major peak in the coarse mode suggest that they were emitted from the sea surface microlayers and/or produced by heterogeneous oxidation of biogenic unsaturated fatty acids on sea salt particles