Abstract
Temporal variability (November'09–March'10) in the mass concentrations of PM2.5, mineral dust, organic carbon and elemental carbon (OC and EC), water-soluble organic carbon (WSOC) and inorganic species (WSIS) has been studied in the atmospheric outflow to the Bay of Bengal from a sampling site [Kharagpur: 22.02°N, 87.11°E] in the Indo-Gangetic Plain (IGP). Based on diagnostic ratios of carbonaceous species [OC/EC≈7.0±2.2, WSOC/OC≈0.52±0.16, and K+/EC≈0.48±0.17], we document dominant impact from biomass burning emissions (wood-fuel and post-harvest agricultural-waste burning) in the IGP-outflow. Relatively high concentration of sulphate (SO42−≈6.9–25.3μgm−3; SO42−/ΣWSIS=45–77%) and characteristic ratios of nss-SO42−/EC (3.9±2.1) and nss-SO42−/OC (0.61±0.46) provide information on absorption/scattering properties of aerosols. Based on quantitative assessment of individual components of PM2.5, we document aerosol organic carbon-to-organic mass (OC to OM) conversion factor centring at 1.5±0.2 (range: 1.3–2.7) in the atmospheric outflow from IGP. The aerosol composition over the Bay of Bengal shows striking similarity with the diagnostic ratios documented for the IGP-outflow. Relatively high conversion factor for assessing the mass of organic aerosols over the Bay of Bengal (1.1–3.7) provides evidence for their oxidation during long-range atmospheric transport.
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