<p>Tropospheric ozone (O₃) is widely recognized as a threat to global food security due to its detrimental effects on crop productivity. Previous studies have determined exposure-response functions, e.g., yield response to O₃ metrics, through controlled O₃ exposure experiments. However, this approach requires substantial cost and time. Therefore, we aimed to derive exposure-response functions epidemiologically and assess the impact of O₃ on the productivity of rice and Japanese mustard spinach in Japan. Accumulated O₃ exposure over a threshold of 40 ppb (AOT40, ppm h) during the growth period was calculated at O₃ monitoring stations and spatially interpolated using the ordinary kriging method, then averaged for each prefecture. We derived the exposure-response relationships between prefecture-scale AOT40 and crop yields using the boundary line technique. Our results clearly demonstrated that yields of both species are reduced with increasing AOT40 levels, showing a decline of 2.01% and 8.24% per unit AOT40 in rice and Japanese mustard spinach, respectively. These sensitivities are broadly consistent with the previous findings from controlled O₃ exposure experiments. While O₃-induced yield reductions estimated using the derived functions varied considerably across prefectures and years, the estimated reductions in total national production were 8.7% and 13.4% for rice and Japanese mustard spinach, respectively, on average during the period from 2010 to 2023. These findings highlight the usefulness of the epidemiological boundary line technique in identifying the exposure-response functions of crop yields to O₃ and the urgent need for mitigation and adaptation strategies to ensure high and stable crop production in Japan.</p> Graphical Abstract <p></p>