Spatiotemporal Simulation Of Ground-level Ozone Concentrations And Its Effect On Crop Yield In The North China Plain

Ground-level ozone has significant negative effects on the crop production.Ozone pollution is a severe environmental issue in China due to the rapid development of industrialization and urbanization leads to increasing precursor emissions of ozone in recent years.The North China Plain（NCP）is one of the major grain producing areas in China.The yields of winter wheat and maize in NCP accounting for 57%and 21%of China’s total yields,respectively.The large amount of nitrogen oxides（NOx）,volatile organic compounds（VOCs）,and other ozone precursors had been discharged,which led to a serious ozone pollution problem.Therefore,it is essential to conduct studies on impacts of ground-level ozone pollution on crop yields in NCP.The ozone pollution indicators based on control experiments and ozone observation data have been adopted to evaluate the impact of ozone pollution on crop yields,such as AOT40（accumulation of hourly ozone concentrations exceed 0.04 ppm）and PODy(phytotoxic ozone dose over a threshold of y nmol m^-2s^-1).The ozone concentration levels of cities and crop areas had large spatial and temporal disparities,but the existing ozone observation data were mainly obtained from sparse environmental monitoring sites in cities.Previous studies used ozone monitoring data of cities or based on the monitoring data to estimate the surface ozone pollution,which can not illustrate the spatial and temporal variation of ozone concentrations accurately.That resulted in great uncertainties in the estimation of effects of ozone pollution on crop yields.To solve this issue,this study adopted WRF-Chem（Weather Research and Forecasting（WRF）model coupled with Chemistry）model to simulate ozone concentrations and meteorological data with high spatial and temporal resolution.These simulations were used to quantify the spatial and temporal variations of the impact of ground-level ozone pollution on winter wheat and maize yields combined with AOT40 and PODy indicators in the NCP.Following is the results of this study:（1）The physical and chemical process parameter were parameterized for WRF-Chem model in NCP.The anthropogenic source emission inventory（MEIC）was regrided for the WRF-Chem model.This study conducted the different combination of physical and chemical process schemes for the sensitivity simulation experiment,which combined with the observation data to evaluate the performance of WRF-Chem model.The sutiable physical and chemical processes were selected for NCP based on the sensitive experiments.（2）Spatial and temporal variations of the ground-level ozone concentrations was simulated in NCP.We simulated the spatial and temporal distributions of ozone concentrations over NCP from 2015 to 2018.Results showed that the ozone pollution level has large spatial and temporal variations in NCP.The most severe ozone pollution occurred in the period of June to August.The high ozone concentrations were mainly distributed in southern and central regions of NCP.We found that the ozone concentrations can cause crop yields loss（average diurnal ozone concentration>0.04 ppm）over most counties of NCP.（3）Impacts of ground-level ozone pollution on yields of winter wheat in NCP.Spatial and temporal variations of AOT40 and POD₁₂(phytotoxic ozone dose over a threshold of 12 nmol m^-2s^-1)index were calculated based on simulated ozone and meteorological data.Losses of winter wheat yield caused by ozone pollution were quantitatively estimated for NCP during 2015-2018.Results showed that AOT40 and POD₁₂had significant spatial and temporal differences during the growing season of winter wheat.The annual mean values of AOT40 and POD₁₂was 7.92 ppm h and 2.41 mmol m^-2at the regional scale,respectively,which had an increasing trend year by year.Winter wheat yields losses due to ozone pollution also had obvious spatial and temporal disparities.The annual mean winter wheat yields loss was around1875.75×10⁴tons in NCP,which is equivalent to an economic loss of 6721.52×10⁶dollars.（4）Impacts of ground-level ozone pollution on the losses of maize yields in NCP.We calculated AOT40 and POD₆(phytotoxic ozone dose over a threshold of 6 nmol m^-2s^-1)indexes based on the simulations of ozone and meteorological data by WRF-Chem model.The spatial and temporal patterns of losses of maize yields due to ozone pollution were estimated in NCP during 2015-2018.Results showed that the annual AOT40 and POD₆had significant spatial and temporal differences during the maize growing seasons,which was 24.82 ppm h and 7.34 mmol m^-2,respectively.These two indexes had an increasing trend year by year.The high value was mainly distributed in southern and central counties of NCP.The annual mean loss of maize yield caused by ozone pollution was around 1801.58×10⁴tons in NCP,which is around the economic loss of 6542.25×10⁶dollars.