First observation-based study on surface O trend in Indo-Gangetic Plain: Assessment of its impact on crop yield.

Tropospheric ozone (O) is an important air pollutant which causes substantial losses in crop production. Increasing O levels in India particularly in Indo-Gangetic Plain (IGP) is a major issue as it is reducing the crop yield. The present study is an attempt to determine the O and its precursor trend using continuous ground-based observations at a suburban site in IGP. The study focuses on the overall characteristics of annual, monthly, diurnal and hourly measurements of O. Annual mean values of O have shown an increment of 19.2% from 2010 to 2015. Similarly, nitrogen oxide (NO) levels increased by 30.2%. O levels at the study site showed a significant increasing trend of 0.7 ppb/yr. The observed O trend was analyzed in terms of changes in NO levels and meteorological parameters. No significant difference in meteorological parameters was observed during 2010-15, however, NO levels have shown an increasing trend of 0.9 ppb/yr. Further to quantify the impact of increasing O on crops, ozone-related crop yield losses for rice and wheat crop were determined for the period 2010-15. AOT40 (accumulated ozone exposure over a threshold of 40 ppb) and M7 (mean 7-h O mixing ratio from 09:00 to 15:59 LT) O exposure metrics were used to calculate the reduction in crop yield during major crop growing seasons: Rabi and Kharif.