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Sources and formation processes of water‐soluble dicarboxylic acids, ω‐oxocarboxylic acids, α‐dicarbonyls, and major ions in summer aerosols from eastern central India
Author(s) -
Deshmukh Dhananjay K.,
Kawamura Kimitaka,
Deb Manas K.,
Boreddy Suresh K. R.
Publication year - 2017
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd026246
Subject(s) - glyoxal , oxalic acid , chemistry , aqueous solution , aerosol , dicarboxylic acid , glyoxylic acid , aqueous two phase system , inorganic chemistry , adsorption , organic chemistry
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 (C 2 ‐C 12 ), ω‐oxoacids (ωC 2 ‐ωC 9 ), α‐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 ω‐oxoacids showed the predominance of glyoxylic acid (ωC 2 ), and glyoxal (Gly) was a major α‐dicarbonyl in all the sizes. Diacids, ω‐oxoacids, and α‐dicarbonyls as well as SO 4 2 − , NO 3 − , andN H 4 + were enriched in coarse mode, where Ca 2+ 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 C 2 /(C 2 ‐C 12 ), C 2 /ωC 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, ωC 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.