Stable carbon isotopic compositions of total carbon, dicarboxylic acids and glyoxylic acid in the tropical Indian aerosols: Implications for sources and photochemical processing of organic aerosols

The tropical Indian aerosols (PM10) collected on day-and nighttime bases in winter and summer, 2007 from Chennai (13.04 degrees N; 80.17 degrees E) were studied for stable carbon isotopic compositions (delta C-13) of total carbon (TC), individual dicarboxylic acids (C-2-C-9) and glyoxylic acid (omega C-2). delta C-13 values of TC ranged from -23.9 parts per thousand to -25.9 parts per thousand (-25.0 +/- 0.6 parts per thousand; n = 49). Oxalic (C-2) (-17.1 +/- 2.5 parts per thousand), malonic (C-3) (-20.8 +/- 1.8 parts per thousand), succinic (C-4) (-22.5 +/- 1.5 parts per thousand) and adipic (C-6) (-20.6 +/- 4.1 parts per thousand) acids and omega C-2 acid (-22.4 +/- 5.5 parts per thousand) were found to be more enriched with C-13 compared to TC. In contrast, suberic (C-8) (-29.4 +/- 1.8 parts per thousand), phthalic (Ph) (-30.1 +/- 3.5 parts per thousand) and azelaic (C-9) (-28.4 +/- 5.8 parts per thousand) acids showed smaller delta C-13 values than TC. Based on comparisons of delta C-13 values of TC in Chennai aerosols to those (-24.7 +/- 2.2 parts per thousand) 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 delta C-13 values of C-9 diacid by about 5 parts per thousand from winter to summer suggests that tropical plant emissions also significantly contribute to organic aerosol in this region. Significant increase in delta C-13 values from C-4 to C-2 diacids in Chennai aerosols could be attributed for their photochemical processing in the tropical atmosphere during long-range transport from source regions.