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A systematic analysis of surface ozone and its precursor gases observed in a semi-arid region centered at Anantapur is presented. The analysis is based on ozone and its precursor gas (NOx and CO) data for the rural station Anantapur, which is about 200 and 400 km from the two nearby major cities, Bangalore to the south and Hyderabad to the north, respectively. Ozone levels were highest during the winter and summer period and lowest during the monsoon. The rate of increase in O-3 is greatest (about 4.7 ppbv/h) around 0900 h local time, whereas the magnitude of the maximum rate of decrease during the evening is considerably smaller (about -3.0 ppbv/h). This feature distinguishes the urban and rural sites since the magnitudes of the rates during morning and evening are more similar at urban sites. A high annual average ozone mixing ratio is observed at Anantapur (35.9 ppbv) in comparison with Gadanki (25 ppbv), Pune (16 ppbv), Ahmedabad (13 ppbv) and Delhi (11 ppbv). At Anantapur, annual averages of oxides of nitrogen (NOx) and CO are observed as 3.9 +/- 0.6 ppbv and 436 +/- 64 ppbv, respectively. (c) 2005 Elsevier B.V. All rights reserved.