Observational studies on the variations in surface ozone concentration at Anantapur in southern India

Abstract

Continuous measurements of surface ozone (O₃) at a semi-arid rural site (14.62°N, 77.65°E) in Anantapur, India during the period from December 2008 to July 2009 are presented. The diurnal variation in O₃ shows high concentrations (in the range of 25-77 ppbv) during daytime and low concentrations during late evening and early morning hours, due to slower titration of ozone by oxides of nitrogen (NO_x). The monthly average high (low) O₃ is 56.09 ± 10.1 ppbv (27.45 ± 2.3 ppbv) at noon in March (July), due to a possible increase in precursor gas concentration by anthropogenic activity and also due to the influence of local meteorological conditions. Furthermore, O₃ concentration has been observed as a function of season, which shows that the highest O₃ concentration is 52.05 ± 10.2 ppbv in the summer and the lowest 30.96 ± 5.7 ppbv in the monsoon season. The rate of the increase of surface ozone is high (2.11 ppbv/h) in March and low (0.32 ppbv/h) in July. Among the meteorological parameters, daily average ozone shows a significantly positive correlation with temperature (R = 0.76) and negative correlation with relative humidity (R = - 0.62). Throughout the study period, high ozone concentrations were mainly associated with the winds from 150.5° to 260.1°. The weekend ozone effect indicates that higher O₃ concentration on weekend compared to weekday suggests that the photochemical production of O₃ is non-linear over this site. The results also show that high aerosol concentration has very strong impact on photochemical activities and ozone formation. The correlation between ozone and aerosol concentrations appears in a non-linear feature. Backward trajectory analysis shows that the increase of ozone concentration and the relatively constant high ozone concentrations during the summer might originate from the transport of ozone rich airmass above the boundary layer especially in Northern India and East Asian regions. On the other hand, the airmasses coming from the south over the Indian Ocean contributes low amount of ozone during the monsoon.