Seasonal heterogeneity in ozone and its precursors (NOx) by in-situ and model observations on semi-arid station in Anantapur (A.P), South India

The continuous measurements of surface ozone (O-3) and oxides of nitrogen (NO3) present in the ambient air were carried out on a semi-arid rural area in Anantapur 114.62 N, 77.65 E], South India during the period beginning from March 2012 to February 2013. The diurnal variation of surface ozone (O-3) showed a minimum at sun rise and late evenings and maximum at noon time, due to slow titration of O-3 with oxides of nitrogen (NOx). The monthly average minimum/maximum of O-3 observed in August/March was 19.9 +/- 0.3/55.8 +/- 2.9 ppbv. The monthly average variation of NO3 was found to be high (6.67 +/- 0.8) in November and noticed low (2.07 +/- 0.2) concentrations in May. The monthly mean maximum of O-3 during day time (night time) was observed as 64.9 +/- 5.3 (45.3 +/- 4.1) ppbv in March, and mean low concentration was about 19.9 +/- 1.02 (12.8 +/- 0.9) ppbv in August. The monthly mean enhanced concentration of NO3 during the day time/night time was about 5.0 +/- 0.6/8.7 +/- 0.9 in November and the fallen concentration was noticed 1.5 +/- 0.2/2.7 +/- 0.3 in May. The spatial distribution of O-3 was associated with the air flow pattern, air mass trajectories and boundary layer heights. The water vapor content also played a significant role in the diurnal variation of O-3 in addition to photo chemistry. The diurnal variation of UV radiation with O-3 and NO3 has been analyzed and the results are reported. And the diurnal and seasonal variations in boundary layer height have also been discussed. The monthly mean variation of aerosol optical depth (AOD) is similar to that of tropospheric ozone, with a correlation coefficient of r = 0.60. The diurnal and seasonal patterns of ozone were simulated using the chemical found to be in good agreement with the observed ones. (C) 2013 Elsevier Ltd. All rights reserved.