Variations of surface ozone levels in urban area of India: a focus on night-time residual concentrations

This study investigates the existing diurnal as well as night time surface ozone concentration trend over Delhi between 1990 and 2012. Secondary data obtained from the National Data Centre (NDC) of the India Meteorological Department (IMD) was analysed to assess the trend in the surface and night-time ozone concentration. This was further used to forecast the variation in the night-time ozone concentration over the city till 2025. A significantly increasing trend of the night-time ozone concentration was observed between 1990 and 2012 evidenced by a +0.158 value of the Mann Kendall test. Moreover, the forecasting of the variations conducted using the Autoregressive Integrated Moving Average (ARIMA) model revealed that the concentration of night-time ozone is expected to increase between the period of 2013 and 2025 if the current trend continues. This is the first study to conduct a trend analysis of night-time ozone concentration for a duration of three decades in the NCT of Delhi. Considering the negative impacts of elevated levels of ozone on the health status of individuals, agricultural productivity and air quality of the city, the present study highlights that it is imperative to take concentrated actions to curb the release of anthropogenic precursors of surface ozone.