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 (14.62°N, 77.65°E, 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<75%) using a Quartz Crystal Microbalance (QCM) in the 25–0.05 μm aerodynamic diameter range. The hourly average total surface aerosol mass concentration in a day varied from 15 to 70 μg m?3, with a mean value of 34.02±9.05 μg m?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 μg m?3 in the month of April, whereas accumulationmode concentration was observed to be high in the winter period contributed >68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, A f (= M a/M t) was highest during winter (mean value of A f ～ 0.80) and lowest (A f ～ 0.64) during the monsoon season. The regression analysis shows that both R eff and R m 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.