The surface level ozone (O 3 ), nitrogen oxides (NO x = NO 2 + NO), volatile organic compounds (VOCs), black carbon (BC) and meteorological parameters were continuously monitored for the period of one year (2010) at an urban site in Hyderabad using different trace gas monitors. The local emissions and meteorology have been found to play a significant role in diurnal variations of O 3 . The average peak time mixing ratios of O 3 were observed in the range of 23 ± 8 to 67 ± 13 ppbv. Diurnalseasonal variation of O 3 and its precursors were also reported. The observed O 3 concentrations were higher during the day than in the night. Maximum O 3 concentrations in the three seasons i.e., summer, winter and monsoon were 56 ± 14 ppbv, 50 ± 9 ppbv, and 28 ± 10 ppbv, respectively. Weekday/weekend variation of O 3 and its precursors were studied during the three seasons. High O 3 concentrations were observed on weekends compared to weekdays, however, NO x and BC levels were found low during weekends. The weekend effect of O 3 was high during winter. The annual average afternoon peak time O 3 levels on weekends were 11% higher than the weekday concentrations. Weekday/weekend variations of NO x at morning traffic rush hour were 14%, 9% and 8% in winter, summer and monsoon, respectively. The annual mean of NO x and BC concentrations at weekend were observed to be lower than weekday about 10% and 9% respectively. VOC/NO x ratio is more (5) during weekend than weekday (4) which resulted in enhanced O 3 formation.

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