Determination of wood burning and fossil fuel contribution of black carbon at Delhi, India: Using aerosol light absorption technique

Friday, 19 December 2014
Suresh Tiwari1, Deewan Singh Bisht1 and Atul Srivastava2,3, (1)Indian Institute of Tropical Meteorology, Air Pollution, New Delhi, India, (2)Indian Institute of Tropical Meteorology, Pune, India, (3)Indian Institute of Tropical Meteorology, Delhi Branch, India
A comprehensive measurement program of effective black carbon (eBC), fine particle (PM2.5) and carbon monoxide (CO) was undertaken during 1st December 2011 to 31st March 2012 in Delhi, India. The mean mass concentrations of eBC, PM2.5 and CO were recorded as 12.1±8.7µg/m3, 182.75±114.5µg/m3 and 3.41±1.6ppm respectively. Also, the Absorption Angstrom exponent (AAE) was estimated from eBC and varied from 0.38 to 1.29 with mean value of 1.09±0.11. The frequency of occurrence of AAE was ~17% less than unity whereas ~83% was greater than unity. The mass concentrations of eBC were found to be higher by ~34% of the average value of eBC (12.1µg/m3) during the study period. Sources of eBC were estimated and they were ~ 94% from fossil fuel (eBCff) combustion whereas only 6% was from wood burning (eBCwb). The ratio between eBCff and eBCwb was fifteen which indicates a higher impact from fossil fuels compared to biomass burning. When comparing eBCff during day and night, a factor of three higher concentrations was observed in night-time than daytime, it is due to combustion of fossil fuel (diesel vehicle emission) and shallow boundary layer conditions. The contribution of eBCwb in eBC was higher in between 18.00 to 21.00 hrs due to burning of wood / biomass. A significant correlation between eBC and PM2.5 (r=0.78) and eBC and CO (r = 0.46) indicates the similarity in location sources. The mass concentration of eBC was highest (23.4μg/m3) during the month of December when the mean visibility (VIS) was lowest (1.31Km). Regression analysis among wind speed (WS), VIS, soot particles and CO were studied and significant negative relationships were seen as VIS and eBC (-0.65), eBCff (-0.66), eBCwb (-0.34) and CO (-0.65), however, in between WS among eBC (-0.68), eBCff (-0.67), eBCwb (-0.28) and CO (-0.53) respectively. The regression analysis indicated that emission of soot particles may be localized to fossil fuel combustion whereas wood/biomass burning emissions of black carbon are due to transportation from farther distances. Regression analysis between eBCff with CO (r=0.44) indicated a similar source as vehicular emissions. The very high loading of PM2.5 along with eBC over Delhi suggests that urgent action is needed to mitigate the emissions of carbonaceous aerosol in the northern part of India.