Increasing tropospheric ozone concentration is a big threat to food security due to its phytotoxicity. It causes a huge damage to crop production across the globe, especially in the C3 plants (paddy (Oryza sativa)). The present study focuses on exposure-plant response index over different O3 concentration. In this study, two metrics viz. the average ozone for 7 h during daytime (M7) and accumulated exposure above a threshold of X ppb (AOTX) have been used in examining crop yield decline in Delhi, India. Eight AOTX indices (AOT0, AOT5, AOT10, AOT15, AOT20, AOT25, AOT30 and AOT40) were analysed and potential crop reduction was predicted. The regular monitoring of O3 was done for 24 hours in year 2013. As per the European benchmark, a 5% yield loss was expected when AOT40 values crosses 3000 ppb·h, however this study revealed that AOT40 threshold value ranged between 695 ppb to 17645 ppb which had exceeded the European benchmark in most of the months. The crop reduction was found to be ~6.3% as evaluated by AOT40 index, whereas, total AOTX contributed up to 23% of rice yield reduction in Delhi NCR. On the other side, only 2% of rice yield loss has been predicted using M7 index, which is not comparable with AOTX indices. The M7 index was also found incomparable to the calculated net yield loss (13%) for year 2013 to 2016. Hence, AOT40 may be a better index to predict the vulnerable impact of O3 into the crop production. The total vulnerability of O3 calculated as 57% in the crops reduction, while impacts of O3 was calculated and summed up for both the significant and non-significant paddy growing seasons. Hence, this study highlights an alarming situation in crop yield reduction due to O3 exposure in Delhi NCR which further threatens food security.
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