Organic and elemental carbon variation in PM2.5 over megacity Delhi and Bhubaneswar, a semi-urban coastal site in India

This paper presents the effect of meteorology, long-range transport, boundary layer and anthropogenic activities on the chemical composition of aerosol (PM2.5) particularly carbonaceous aerosol (OC, EC TC) in two Indian cities, namely Delhi and Bhubaneswar. The climatological and demographical differences in the two cities have compelled the authors to compare concentrations of atmospheric organic carbon (OC) and elemental carbon (EC) in PM2.5 at Delhi and Bhubaneswar during winter 2013 (Dec 2012 to Feb 2013). Although, Delhi is a densely populated megacity with several anthropogenic activities, Bhubaneswar is a comparatively less dense small coastal city. The percentage contribution of total carbon (TC) to PM2.5 mass was higher as recorded at Bhubaneswar (similar to 30.38 %) as compared to Delhi (similar to 15 %). Average ratios of OCtot/EC, K+/OCtot and K+/EC were recorded as 1.88 +/- A 0.24, 0.006 +/- A 0.004 and 0.018 +/- A 0.013 at Bhubaneswar, respectively, whereas in Delhi, respective average ratios of OCtot/EC, K+/OCtot and K+/EC were recorded as 1.37 +/- A 0.16, 0.230 +/- A 0.066 and 0.321 +/- A 0.122. OCtot/EC, K+/OCtot, K+/EC ratios and eight carbon fraction analysis of PM2.5 mass revealed the dominant contribution of fossil fuel specifically from coal combustion at Bhubaneswar, whereas vehicular exhaust, fossil fuel combustion along with biomass burning and road dust were the main sources of emission at Delhi. Long-range transport and prevailing meteorology had a major impact on the respective pollutants at Bhubaneswar, and OCtot and EC of PM2.5 mass over Delhi were believed to have originated from local sources due to shallow boundary layer, stable meteorology and high anthropogenic activities during the observation period. Besides, secondary organic carbon (OCsec) contributed 15.76 +/- A 8.41 and 14.65 +/- A 7.46 % to OCtot concentration of Bhubaneswar and Delhi, respectively.