资源环境科技发展态势分析平台

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 degrees N and 82.3 degrees E) in eastern central India during summer of 2013 were measured for water-soluble diacids (C-2-C-12), omega-oxoacids (omega C-2-omega C-9), alpha-dicarbonyls (C-2-C-3), and inorganic ions to better understand their sources and formation processes. Diacids showed the predominance of oxalic acid (C-2), whereas omega-oxoacids showed the predominance of glyoxylic acid (omega C-2), and glyoxal (Gly) was a major alpha-dicarbonyl in all the sizes. Diacids, omega-oxoacids, and alpha-dicarbonyls as well as SO42-, NO3-, and NH4+ 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 NO3- (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 C-2/(C-2-C-12), C-2/omega C-2, and C-2/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 C-2 diacid through aqueous-phase oxidation of its higher homologous diacids, omega C-2, 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.