Potential source regions contributing to seasonal variations of black carbon aerosols over Anantapur in Southeast India

Abstract

Continuous measurements of black carbon (BC) mass concentration performed at Anantapur [14.62°N, 77.65°E, 331 m asl], a suburban location in southeast India, using an Aethalometer from January to December, 2010, are analyzed and discussed here. The annual mean BC mass concentration ([BC]) was 3.03 ± 0.27 µg/m³ for the above study period. The sharp morning (fumigation) peak occurs between 07:00 and 08:00 h almost an hour after the local sunrise while a broad evening (nocturnal) peak is at ~21:00 h with a minimum in noon hours (14:00–16:00 h). The seasonal mean values of [BC] are 5.05 ± 0.51 μg/m³ in the winter, 3.77 ± 1.23, 1.55 ± 0.51, and 2.33 ± 0.82 µg/m³ in the summer, monsoon and postmonsoon seasons, respectively. High BC values tend to occur when the wind is directed from the 180–225° sector, which may be well defined by the geographical location of the observation site. During the winter, the trajectory air mass pathways originated through north or central India with significant advection of continental aerosols arriving before the measurement region, results in an enhanced [BC]. Whereas in the monsoon season, the pristine marine air mass from the oceanic environment led to decrease in the concentration of BC. Comparison of monthly mean variations in AOD at 500 nm and black carbon aerosols is observed to be positive with poor correlation coefficient of 0.42. The ratio of BC/PM2.5 varied from 1.3% to 7.2% with a mean value of 4.6% at Anantapur during the observation period and this ratio decreased with decreasing Ångström exponent (alpha).