Seasonal and diurnal variation of surface ozone and a preliminary analysis of exceedance of its critical levels at a semi-arid site in India

The mixing ratios of surface O-3 were measured at St. John's College, Agra, an urban and traffic influenced area for the period of 2000-2002. The monthly averaged O-3 mixing ratios ranged between 8 to 40 ppb with an annual average of 21 ppb. Strong diurnal and seasonal variations in O-3 mixing ratios were observed throughout the year except for monsoon season. The mixing ratios of O-3 follow the surface temperature cycle and solar radiation (r = 0.72 and r = 0.65 with temperature and solar radiation, respectively). Concentrations were higher with winds associated with NE and NW direction indicating the impact of pollution sources on surface O-3 concentration. Exceedance of ozone critical level was calculated using the AOT 40 index and found to be 840 ppb.h and 2430 ppb.h for summer and winter seasons, respectively. The present O-3 exposures are lower than the critical level of O-3 and suggest that the present level of O-3 does not have any impact on reduction in crop yields.