Rice yield reductions due to ozone exposure and the roles of VOCs and NOx in ozone production in Japan

Ozone (O3) is believed to be the most damaging air pollutant to crops, owing to its ability to decrease physiological functions, including photosynthesis. Accordingly, it has been reported that rice yields have been drastically reduced by O3 exposure. However, previous studies have not assessed the impacts of O3 on rice, nor assessed the fine-scale comprehensive relationships between O3 sensitivity regimes and volatile organic compound (VOC) and NOx emissions throughout Japan. In this study, a combined Weather Research and Forecasting with Chemistry (WRF-Chem) model was used with anthropogenic emission, biomass burning, and biogenic emission data to evaluate the impacts of surface O3 on reduced rice yields in Japan in 2010. The relative yield loss due to O3 damage was evaluated using the accumulated ozone exposure over a threshold of 40 ppb (AOT40) and a mean 7 hour ozone mixing ratio (M7). The differences between the measured and simulated O3 data indicate that the WRF-Chem model simulated the surface O3 concentration adequately. At a national scale, the aggregated average relative yield losses in Japan were estimated to be 4.3% for AOT40 and 2.0% for M7, while aggregated rice production loss was 482 Kt for AOT40 and 218 Kt for M7. In particular, the greatest rice production loss was observed in the Kanto region (126 Kt for AOT40 and 54 Kt for M7). In addition, the model results indicate that isoprene and formaldehyde (CH2O) are critical for the atmospheric oxidation of surface O3 in the Kanto region. Although there are uncertainties associated with the growing period, cultivar, emission inventories, and rice sensitivity to O3 concentrations, the results of this study provide an important scientific basis for attaining more sustainable food production.