Ozone formation and destruction at a sub-urban site in North Central region of India

A systematic analysis of surface ozone and its precursor (NO and NO2) was carried out at Dayalbagh, a suburban site using continuous online O3 and NOx analyzers from November 2008 to October 2009. Diurnal patterns in ozone concentration show daytime maxima (50–60 ppbv) around 1200–1400 h due to in situ photochemical production and minimum (7–10 ppbv) during night time. O3 followed inverse relationship with its precursor, NO2. Seasonal variations in ozone concentration show pronounced maxima in the summer and winter seasons and minima in monsoon and postmonsoon seasons. The high ozone episode days during peak summer were associated with meteorological parameters such as sunny and warm weather, and low relative humidity. The seasonal average concentration in summer ranged between 42 and 45 ppbv, between 28 and 30 ppbv in winters, and between 20 and 23 ppbv in postmonsoon whereas, it is found to be 9–16 ppbv in the monsoon season. The rate of formation as evaluated from 0800 to 1000 h was observed to be maximum in the month of April (4.4 ppbv/h) and minimum in the month of August (0.4 ppbv/h). On the other hand, the rate of destruction of O3 from 1700 to 1900 h was found to be maximum in February (− 4.2 ppbv/h) and minimum in the month of August (− 0.3 ppbv/h). On the basis of Environmental Protection Agency classification, 8-h ozone concentration remained good for 90% of days, moderate for 8.1% of the days, unhealthy for sensitive groups for 1.9% of the days during the study period.