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 (O3) and oxides of nitrogen (NOx) present in the ambient air were carried out on a semi-arid rural area in Anantapur [14.62° N, 77.65° E], South India during the period beginning from March 2012 to February 2013. The diurnal variation of surface ozone (O3) showed a minimum at sun rise and late evenings and maximum at noon time, due to slow titration of O3 with oxides of nitrogen (NOx). The monthly average minimum/maximum of O3 observed in August/March was 19.9 ± 0.3/55.8 ± 2.9 ppbv. The monthly average variation of NOx 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 O3 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 NOx 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 O3 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 O3 in addition to photo chemistry. The diurnal variation of UV radiation with O3 and NOx 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 box model (NCAR Mater Mechanism) and when compared with the observed ones, the results are found to be in good agreement with the observed ones.