First observation-based study on surface O3 trend in Indo-Gangetic Plain: Assessment of its impact on crop yield.

Tropospheric ozone (O3) is an important air pollutant which causes substantial losses in crop production. Increasing O3 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 O3 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 O3. Annual mean values of O3 have shown an increment of 19.2% from 2010 to 2015. Similarly, nitrogen oxide (NOx) levels increased by 30.2%. O3 levels at the study site showed a significant increasing trend of 0.7 ppb/yr. The observed O3 trend was analyzed in terms of changes in NOx levels and meteorological parameters. No significant difference in meteorological parameters was observed during 2010-15, however, NOx levels have shown an increasing trend of 0.9 ppb/yr. Further to quantify the impact of increasing O3 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 O3 mixing ratio from 09:00 to 15:59 LT) O3 exposure metrics were used to calculate the reduction in crop yield during major crop growing seasons: Rabi and Kharif.