Characteristics of surface ozone in Agra,a sub-urban site in Indo-Gangetic Plain

In the present study, measurements of surface ozone ((hbox {O}_{3})) and its precursors (NO and (hbox {NO}_{2})) were carried out at a sub-urban site of Agra ((27{^{circ }}10'hbox {N}), (78{^{circ }}05'hbox {E})), India during May 2012–May 2013. During the study period, average concentrations of (hbox {O}_{3}), NO, and (hbox {NO}_{2}) were (39.6 pm 25.3), (0.8 pm 0.8) and (9.1 pm 6.6 , hbox {ppb}), respectively. (hbox {O}_{3}) showed distinct seasonal variation in peak value of diurnal variation: summer ({>}) post-monsoon ({>}) winter ({>}) monsoon. However, (hbox {NO}_{2}) showed highest levels in winter and lowest in monsoon. The average positive rate of change of (hbox {O}_{3}) (08:00–11:00 hr) was highest in April (16.3 ppb/hr) and lowest in August (1.1 ppb/hr), while average negative rate of change of (hbox {O}_{3}) (17:00–19:00 hr) was highest in December (–13.2 ppb/hr) and lowest in July (–1.1 ppb/hr). An attempt was made to identify the (hbox {VOC--NO}_{mathrm{x}}) sensitivity of the site using (hbox {O}_{3}/hbox {HNO}_{3}) ratio as photochemical indicator. Most of the days this ratio was above the threshold value (12–16), which suggests (hbox {NO}_{mathrm{x}}) sensitivity of the site. The episodic event of ozone was characterized through meteorological parameters and precursors concentration. Fine particles ((hbox {PM}_{2.5})) cause loss of ozone through heterogeneous reactions on their surface and reduction in solar radiation. In the study, statistical analyses were used to estimate the amount of ozone loss.