Simultaneous measurements of surface ozone at two sites over the southern Asia: A comparative study

This article presents variations of simultaneous measurements of near surface ozone (O ₃) at two sites namely Anantapur [14.62°N, 77.65°E], a semi arid rural location in India and Xi'An [34.20°N, 108.98°E], a semi arid urban location in China during January-July 2009. The results showed a clear diurnal cycle of O ₃ with a minimum at sunrise and a maximum at noon for both the sites. The monthly average diurnal variation shows that the maximum/minimum ozone was observed in March/July whereas in Xi'An maximum/minimum ozone was observed in July/February because of different climatic zones and rainfall activity. The average diurnal variation of O3 for different seasons (summer and winter) shows higher ozone concentration at Anantapur than at Xi'An. This may be due to slower titration of NO in the evening hours at Anantapur. But in Xi'An, the highest ozone levels recorded in noon hours for some days in June and July months. This is mainly due to strong emissions of NO _x, VOC and high solar radiation and this implies significant negative effects on vegetation and regional air quality around Xi'An. The rate of increase of ozone is almost the same at two sites but the rate of decrease of ozone is more at Xi'An than at Anantapur which is due to the higher NO _x concentration from vehicular emission and also due to the fast titration of O ₃. The maximum 54% of frequency distribution of ozone lies between 20-45 ppbv at Anantapur whereas in Xi'An 34% lies in the range of 0-5 ppbv, 32% of Ozone lie between 5-20 ppbv and 24% of all O ₃ lie in the range of 20-45 ppbv.