Analysis of the effect of troposphere ozone on grain production in North China Plain and Yangtze River Delta

　Tropospheric ozone (O₃) is known to harm crops by intrinsically affecting photosynthesis and other functions during crop growth. In staple crop production bases in the North China Plain (NCP) and Yangtze River Delta (YRD) regions, food security, especially food production, has been reported to be threatened by high O₃ concentrations. Studies have been conducted in the NCP or YRD to understand tropospheric O₃ and its precursor gases; however, the need to understand the effect of O₃ on crops in conjunction with the contributions of precursor gases (VOCs and NO_x) to O₃ formation using a fine-scale model remains. In this study, the combined Weather Research and Forecast with Chemistry (WRF-Chem) model was used to evaluate the impact of surface O₃ on reduced grain yield in China in 2010, covering the crop-growing seasons of single rice, double late rice, and winter wheat. The relative yield loss due to O₃ damage was evaluated using the accumulated O₃ exposure over a threshold of 40 ppb (AOT40) and a mean 7-hour O₃ mixing ratio (M7). The validation showed that the gas-phase chemistry mechanism Model for Ozone and Related chemical tracers, version 4 (MOZART-4), coupled with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) aerosol module registered in WRF-Chem, can simulate O₃ fairly in the NCP and YRD. The aggregated average rice (wheat) relative yield losses throughout NCP and YRD were estimated to be 5.9% (27.1%) for AOT40 and 2.2% (9.6%) for M7, whereas aggregated rice (wheat) production losses were 2,345 kt (13,947 kt) for AOT40 and 999 kt (3,753 kt) for M7. In addition, reducing anthropogenic emissions of Volatile Organic Compounds (VOCs) from the energy and transport sectors is effective in reducing the surface O₃ concentration. The results provide important scientific evidence for achieving sustainable food production in China.