Articles | Volume 16, issue 8
Atmos. Chem. Phys., 16, 5263–5282, 2016
https://doi.org/10.5194/acp-16-5263-2016
Atmos. Chem. Phys., 16, 5263–5282, 2016
https://doi.org/10.5194/acp-16-5263-2016

Research article 27 Apr 2016

Research article | 27 Apr 2016

Dicarboxylic acids, oxoacids, benzoic acid, α-dicarbonyls, WSOC, OC, and ions in spring aerosols from Okinawa Island in the western North Pacific Rim: size distributions and formation processes

Dhananjay K. Deshmukh1,a, Kimitaka Kawamura1,a, Manuel Lazaar1,2, Bhagawati Kunwar1, and Suresh K. R. Boreddy1 Dhananjay K. Deshmukh et al.
  • 1Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
  • 2Ecole National Supérieure de Chimie de Rennes (ENSCR), Rennes 35708, France
  • anow at: Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan

Abstract. Size-segregated aerosols (nine stages from < 0.43 to > 11.3 µm in diameter) were collected at Cape Hedo, Okinawa, in spring 2008 and analyzed for water-soluble diacids (C2–C12), ω-oxoacids (ωC2ωC9), pyruvic acid, benzoic acid, and α-dicarbonyls (C2–C3) 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 (C2) was found to be the most abundant species, followed by malonic and succinic acids, whereas glyoxylic acid (ωC2) was the dominant oxoacid and glyoxal (Gly) was more abundant than methylglyoxal. Diacids (C2–C5), ωC2, and Gly as well as WSOC and OC peaked at fine mode (0.65–1.1 µm) whereas azelaic (C9) and 9-oxononanoic (ωC9) acids peaked at coarse mode (3.3–4.7 µm). Sulfate and ammonium were enriched in fine mode, whereas sodium and chloride were in coarse mode. Strong correlations of C2–C5 diacids, ωC2 and Gly with sulfate were observed in fine mode (r =  0.86–0.99), indicating a commonality in their secondary formation. Their significant correlations with liquid water content in fine mode (r =  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 =  0.85–0.96), which is a tracer of biomass burning. Bimodal size distributions of longer-chain diacid (C9) and oxoacid (ωC9) 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.

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Short summary
Size-segregated aerosols in nine size bins were collected in spring 2008 at Cape Hedo, Okinawa, in the western North Pacific Rim, and measured for diacids and related polar compounds. Oxalic acid, glyoxylic acid, and glyoxal peaked at 0.65–1.1 µm in fine mode, suggesting their secondary formation possibly in aerosol aqueous phase. Their strong correlations with liquid water content in fine mode further suggest an importance of the aqueous-phase production in Okinawa aerosols.
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