Diurnal and seasonal variabilities in surface ozone and its precursor gases at a semi‐arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

Abstract

Measurements of surface ozone and its precursor gases (NOx and CO) have been made at a semi‐arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in tropical Indian region for the period, 2001–2003. NOx and CO levels were the highest during morning and late night hours at this site. Diurnal variations of ozone concentrations varied from 25 ppbv to 50 ppbv and were observed to increase gradually after sunrise, attaining a maximum value by the evening and decreasing gradually thereafter. During monsoon months, the diurnal amplitude of ozone was found to be small (20–25 ppbv). Seasonal variation in ozone showed a pronounced maximum (40–50 ppbv) in the winter and summer. Local pollutants were major contributors to the ozone levels during this period. Ozone shows a yearly mean mixing ratio of about 35.9 ± 8.8 ppbv. The daytime concentration of CO and NOx varied between 200 to 1200 ppbv and 3 to 20 ppbv respectively for the period studied. Annual average mixing ratios of oxides of nitrogen (NOx) and CO were observed to be 3.9±0.6 ppbv and 436±64 ppbv, respectively.