Ground-Based In Situ Measurements of Near-Surface Aerosol Mass Concentration over Anantapur: Heterogeneity in Source Impacts

Surface measurements of aerosol physical properties were made at Anantapur (14.62oN, 77.65oE, 331 m a.s.l), a semiarid rural site in India, during August 2008--July 2009. Measurements included the segregated sizes of aerosolsas as well as total mass concentration and size distributions of aerosols measured at low relative humidity (RH-3, with a mean value of 34.02±9.05 μm-3 for the entire study period. A clear diurnal pattern appeared in coarse, accumulation and nucleation-mode particle concentrations, with two local maxima occurring in early morning and late evening hours. The concentration of coarse-mode particles was high during the summer season, with a maximum concentration of 11.81±0.98 μm-3 in the month of April, whereas accumulation-mode concentration was observed to be high in the winter period contributed >68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, Af (= Ma/Mt) was highest during winter (mean value of Af ～0.80) and lowest (Af ～0.64) during the monsoon season. The regression analysis shows that both Reff and Rm are dependent on coarse-mode aerosols. The relationship between the simultaneous measurements of daily mean aerosol optical depth at 500 nm (AOD500) and PM2.5 mass concentration (PM2.5) shows that surface-level aerosol mass concentration increases with the increase in columnar aerosol optical depth over the observation period.