High-energy radiations, such as alpha and beta particles or gamma radiation, ionize air molecules into pairs of positive ions and free electrons. The diurnal and seasonal variations of these air ions were measured for the first time at a rural monitoring station in Ramanandnagar (17°2'N, 74°E),India, and the urban tropical station in Pune (18°31'N, 73°55'E) from June 2007 to May 2008. Air ion concentrations, measured using a Gerdien condenser at Pune station, increased from nighttime and reached maximum in the early morning. Compared to Pune, air ion concentration and positive-to-negative air ion ratios at Ramanandnagar increased from morning and reach maximum in the afternoon (12:00–14:00). Plant transpiration and waves in the flooded Krishna River during July–September 2007 were determined as additional sources of atmospheric ion production at Ramanandnagar. Intensive temperature inversion during winter lead to the accumulation of radon and radioactive aerosols near the Earth’s surface, and hence increased the rate of ionization. Annual peaks of positive/negative ion maxima and positive-to-negative small ion ratios were observed in January 2008. It was also observed that as human activities increased, more aerosol particles were introduced into the atmosphere between 12:00–14:00 hours, during which time the average positive-to-negative air ion ratio reached peak values. During summer, radioactive gases moved upward, carrying radon and radioactive aerosols, and thereby reducing ionization. Results show a decrease in average positive and negative small ion maxima from February 2008 to May 2008.