Ground-based in situ measurements of near-surface aerosol mass concentration over Anantapur: Heterogeneity in source impacts

Abstract

Surface measurements of aerosol physical properties were made at Anantapur (14.62A degrees N, 77.65A degrees 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 mu m aerodynamic diameter range. The hourly average total surface aerosol mass concentration in a day varied from 15 to 70 mu g m(-3), with a mean value of 34.02 +/- 9.05 mu g 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 mu g 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 (AOD(500)) 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.