Sources and formation processes of water-soluble dicarboxylic acids, [omega]-oxocarboxylic acids, [alpha]-dicarbonyls, and major ions in summer aerosols from eastern central India

The 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), [omega]-oxoacids ([omega]C2-[omega]C9), [alpha]-dicarbonyls (C2-C3), and inorganic ions to better understand their sources and formation processes. Diacids showed the predominance of oxalic acid (C2), whereas [omega]-oxoacids showed the predominance of glyoxylic acid ([omega]C2), and glyoxal (Gly) was a major [alpha]-dicarbonyl in all the sizes. Diacids, [omega]-oxoacids, and [alpha]-dicarbonyls as well as SO 4 2 -, NO 3 -, and N H 4 + 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 NO 3 - (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/[omega]C2, 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, [omega]C2, 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. Key Points High abundances of diacids and related SOA in coarse mode Oxalic acid was subjected to aqueous-phase processing in coarse mode Increasing AWC is favorable for oxalic acid formation in coarse mode