Surface levels of Ozone and its precursor NO2 during winter season at urban and rural sites of a semi arid region in India

Ozone is produced from oxygen atoms formed in the photolysis of nitrogen dioxide (NO2) emitted from automobiles and factories. Ozone is considered as a major component of photochemical smog and toxic air pollutants to living things. Measurements of surface ozone and its precursor gas NO2 have been made over an urban and rural site of Agra, the city of Taj Mahal during winter season 2002-2003. Ozone and NO2 show diurnal variations to both the sites during winter season. During the day, the average amount of ozone increases due to active photochemical production mechanism along with favorable meteorological conditions and the related increasing precursor's concentration. The overall increase of ozone is attributed to the increase in NO2 and other precursor's emissions by different sources in the proximity of both the sites. Observations shows that there exists a significant diurnal cycle of average O3 with a maximum concentrations 117.0 µg/m3 in the peak noontime and average minimum O3 concentrations 23.16 µg/m3 at sunrise. The average concentration of ozone was found to be 53.59 µg/m3 and it ranges from 2.35-135.46 µg/m3 whereas the average concentration of NO2 was 124.64 µg/m3 and it ranges from 3.95-351.82 µg/m3. The coefficient of determination of regression curve between O3 and NO2 were R2 = 0.45731 at urban area and R2 = 0.267941 at rural area indicating positive correlation.