Anthropogenic impact on the temporal variations of black carbon and surface aerosol mass concentrations at a tropical semi-arid station in southeastern region of India

Collocated measurements of black carbon (BC) and composite aerosol mass concentrations were continuously monitored at Anantapur (14.62°N, 77.65°E, 331 m asl), a tropical semi-arid station in southeastern region of India, using Aethalometer and a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor, respectively during August 2009–July 2010. Diurnal and seasonal variations of BC and near surface aerosols in relation to changes in the regional meteorological conditions, frequency distribution of BC for different seasons, week days and weekend days effect on BC concentration and size distributions of near surface aerosols were observed. Also, using the HYSPLIT model, back-trajectories were studied to assess the sources for transported particles. Diurnal variation of BC showed two peaks, one in the morning and another in the evening, which were mostly related to the daily changes in the local boundary layer. BC concentrations were maximum during the winter (4.76 ± 0.97 μg m−3), and minimum concentrations were observed in the monsoon (1.44 ± 0.26 μg m−3). The total mass concentration exhibits a high value in the summer (48.89 ± 2.57 μg m−3) and it remains low in the monsoon (30.33 ± 1.65 μg m−3) period. The maximum BC mass fraction was found to be 9.4% in the winter and a minimum of 4.6% in the monsoon.

► BC and total aerosol mass concentrations exhibit well-defined diurnal and annual variations.
► The highest value of BC mass concentration is observed in the winter and the lowest during the monsoon.
► The total mass concentration noticed to be higher in summer and lower in monsoon periods.
► BC mass fraction is estimated as a 6.5% for the observation site.
► The higher values of Reff in the winter suggest that the relative abundance of coarse mode aerosols and vice-versa.