Abstract
[1] The tropical Indian aerosols (PM10) collected on day- and nighttime bases in winter and summer, 2007 from Chennai (13.04°N; 80.17°E) were studied for stable carbon isotopic compositions (δ13C) of total carbon (TC), individual dicarboxylic acids (C2-C9) and glyoxylic acid (ωC2). δ13C values of TC ranged from −23.9‰ to −25.9‰ (−25.0 ± 0.6‰; n = 49). Oxalic (C2) (−17.1 ± 2.5‰), malonic (C3) (−20.8 ± 1.8‰), succinic (C4) (−22.5 ± 1.5‰) and adipic (C6) (−20.6 ± 4.1‰) acids and ωC2 acid (−22.4 ± 5.5‰) were found to be more enriched with 13C compared to TC. In contrast, suberic (C8) (−29.4 ± 1.8‰), phthalic (Ph) (−30.1 ± 3.5‰) and azelaic (C9) (−28.4 ± 5.8‰) acids showed smaller δ13C values than TC. Based on comparisons of δ13C values of TC in Chennai aerosols to those (−24.7 ± 2.2‰) found in unburned cow-dung samples collected from Chennai and isotopic signatures of the particles emitted from point sources, we found that biofuel/biomass burning are the major sources of carbonaceous aerosols in South and Southeast Asia. The decrease in δ13C values of C9 diacid by about 5‰ from winter to summer suggests that tropical plant emissions also significantly contribute to organic aerosol in this region. Significant increase in δ13C values from C4 to C2 diacids in Chennai aerosols could be attributed for their photochemical processing in the tropical atmosphere during long-range transport from source regions.
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