Atmospheric aerosol samples were collected from an urbanized area (Tirupati, South India) during the period April to September 2001 and were analyzed for major inorganic ions-F, Cl, NO3, SO4, Na, K, Mg, Ca and NH4 by employing the ion chromatograph. The average mass of the aerosol was found to be 55.64 mug m(-3) with a total water-soluble load (total anion + total cation) of 5.74 mug m(-3). Seasonal distribution of the aerosol mass and temporal variations of the ion concentrations present a clear trend of lowering atmospheric levels during the rainy season due to washout effect. Composition of the aerosols showed higher concentration of SO4 followed by NO3 and NH4 and found to be influenced by local terrestrial sources. The presence of SO4 and NO3 may be due to re-suspension of soil particles (formation by heterogeneous oxidation). Ca, Mg and Cl are mainly soil derived ones. The presence of NH4 may be attributed to the reaction of NH3 vapors with acidic gases such as H2SO4, HNO3 and HCl or ammonia vapor may react or condense on an acidic particle surface of anthropogenic origin. Equivalent ratios of NH4/(NO3 + SO4) varied between 0.62 and 0.74. It shows the aerosol to be slightly acidic due to the neutralization of basicity by SO2 and NOx. (C) 2002 Elsevier Science B.V All rights reserved.