Sources and formation processes of water‐soluble dicarboxylic acids, ω‐oxocarboxylic acids, α‐dicarbonyls, and major ions in summer aerosols from eastern central India

Abstract

AbstractThe sources and formation processes of dicarboxylic acids are still under investigation. Size‐segregated aerosol (nine‐size) samples collected in the urban site (Raipur: 21.2°N and 82.3°E) in eastern central India during summer of 2013 were measured for water‐soluble diacids (C2‐C12), ω‐oxoacids (ωC2‐ωC9), α‐dicarbonyls (C2‐C3), and inorganic ions to better understand their sources and formation processes. Diacids showed the predominance of oxalic acid (C2), whereas ω‐oxoacids showed the predominance of glyoxylic acid (ωC2), and glyoxal (Gly) was a major α‐dicarbonyl in all the sizes. Diacids, ω‐oxoacids, and α‐dicarbonyls as well as , , and were enriched in coarse mode, where Ca2+ peaked, suggesting that they are preferentially produced in coarse mode via adsorption as well as heterogeneous and aqueous‐phase oxidation reaction of precursors on the surface of water‐soluble mineral dust particles having more alkaline species. Strong correlations of diacids and related compounds with (r = 0.66–0.91) and aerosol water content (AWC) (r = 0.63–0.93) further suggest the importance of heterogeneous and aqueous‐phase production in coarse mode. We found strong correlations of C2/(C2‐C12), C2/ωC2, and C2/Gly ratios with AWC in coarse mode (r = 0.83, 0.86, and 0.85, respectively), indicating that enhanced AWC is favorable for the production of C2 diacid through aqueous‐phase oxidation of its higher homologous diacids, ωC2, and Gly. These results demonstrates unique reactivity of water‐soluble mineral dust particles for the enhanced production of diacids and related compounds in aqueous‐phase, having implications on the aerosol‐cloud interaction, solubility, and hygroscopicity of a dominant fraction of water‐soluble organic aerosol mass.