Journal of Earth Science & Climatic Change
Open Access

Abstract

High emissions of anthropogenic aerosols over Indo-Gangetic Plains (IGP) inspired continuous measurements of fine particles (PM 2.5 ), carbonaceous aerosols (BC, OC and EC), oxides of nitrogen (NOx) and estimation of light extinction (b ext ) and absorption (b abs ) coefficients over Delhi during high pollution season in winter from December 2011 to March 2012. During study period, the mass concentrations of PM 2.5 , BC and NOX were 186.5±149.7μg m-3 , 9.6±8.5μg m -3 and 23.8±16.1 ppb, respectively. The mass concentrations of OC and EC were studied by two different techniques (i) off-line (gravimetric method) and (ii) semi-continuous (optical method) and their mean mass concentrations were 51.1±15.2, 10.4±5.5 μgm -3 and 33.8±27.7, 8.2±6.2 μgm -3 , respectively during the study period. The ratios of mass concentration of OC to EC in both cases were in between 4 to 5. The source contribution of carbonaceous aerosols in PM 2.5 estimated over 24 hrs, during day- and night-time where motor vehicles accounted for ~69%, 90% and 61% whereas coal combustion accounted for ~31%, 10% and 39%, respectively. The estimated mean values of bext and babs over the station were 700.0±268.6 and 71.7±54.6 Mm −1 , respectively. In day and night analysis, bext is ~37% higher during night-time (863.4Mm −1 ) than in day-time (544.5 Mm −1 ). Regression analysis between bext and visibility showed significant negative correlation (r=-0.85). The largest contribution in the light extinction coefficients was found to be due to organic carbon (~46%), followed by elemental carbon (~24%), coarse mode particles (~18%), ammonium sulfate (~8%) and ammonium nitrate (~4%). The individual analysis of light extinction due to chemical species and coarse mode particles indicates that scattering type aerosols is dominated by ~76% over the absorbing type. The aforementioned results suggest that the policy-induced control measures at local administration level are needed to mitigate the excess emissions of carbonaceous aerosols over IGP region which ranks highest in India and elsewhere in worldwide.

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