Publication Date:
2014-02-13
Description:
[1] Water-soluble organic carbon (WSOC) is a major constituent (~ 20-80%) of the total organic carbon aerosol over the Indian subcontinent during the dry winter season. Due to its multiple primary and secondary formation pathways, the sources of WSOC are poorly characterized. In this study, we present radiocarbon constraints on the biomass vs fossil sources of WSOC in PM 2.5 for the 2010/11 winter period for the megacity Delhi, situated in the northern part of the heavily polluted Indo-Gangetic Plain. The fossil fuel contribution to Delhi WSOC (21 ± 4%) is similar to that recently found at two South Asian background sites. In contrast, the stable carbon isotopic composition of Delhi WSOC is less enriched in 13 C relative to that at the two receptor sites. Although potentially influenced also by source variability, this indicates that near source WSOC is less affected by atmospheric aging. In addition, the light absorptive properties of Delhi WSOC were studied. The mass absorption cross section at 365 nm (MAC 365 ) was 1.1 – 2.7 m 2 /g with an Absorption Ångström Exponent (AAE) ranging between 3.1 and 9.3. Using a simplistic model the relative absorptive forcing of the WSOC compared to elemental carbon (EC) in 2010/11 wintertime Delhi was estimated to range between 3-11%. Taken together, this near-source study shows that WSOC in urban Delhi comes mainly (79%) from biomass burning/biogenic sources. Furthermore it is less influenced by photochemical aging compared to WSOC at S Asian regional receptor sites and contributes with a relatively small direct absorptive forcing effect.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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