Investigation of aerosol black carbon over semi-urban and urban locations in south-western India

Abstract

Abstract Temporal evolution of the ‘dual-spot’ 7-channel Aethalometer measured black carbon (BC) aerosols over different time scales, their potential source regions and impact of meteorology on BC mass are analyzed using observational data at Ahmednagar College (AC-Ahmednagar), Ahmednagar and Indian Institute of Tropical Meteorology, Pashan (IITM-Pashan), Pune. Results reveal well defined bimodal diurnal pattern in BC mass; one in morning (07:00-09:00 LT) and another in evening (around 20:00 LT) at both sites. This is quite consistent with seasonally changing BC mass and is the combined effects of variations in anthropogenic emissions, meteorology and associated atmospheric boundary layer (ABL) dynamics. BC mass concentration at AC-Ahmednagar and IITM-Pashan varied from 1.8 to 49.0 μg m−3 (annual mean 13.8 ± 10.4 μg m−3) and 0.7–21.6 μg m−3 (annual mean 3.9 ± 2.8 μg m−3) respectively. Annual BC cycle at AC-Ahmednagar, IITM-Pashan, Delhi and Xian (China) appears to be similar. However, BC mass at AC-Ahmednagar being of the same order to that reported at Delhi (India) and Xi'an (China), it is about 3.5 times higher than at IITM-Pashan. The present work, further, demonstrates prominent role exerted by surface temperature (T) and relative humidity (RH) in modulating BC mass. Occurrence of high ΔBC (BC370 nm – BC880 nm) and absorption Angstrom exponent (AAE) are indicative of enhanced absorption in near-UV and low-visible wavelengths attributed to the presence of biomass burning and light absorbing particulate matter. The back-trajectory cluster and concentrated weighted trajectory (CWT) analysis identifies four distinct potential BC source regions at the present receptor sites.