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Regional ozone (O3) pollution has currently become an urgent air pollution problem in China. Nitrogen oxides (NOX) are key precursor pollutants for O3 formation. However, pollution control policies have generally neglected or simplified the impacts of soil NOX emissions in rural regions. This study aims to evaluate the effect of soil NOX emissions on O3 in agricultural areas of China based on high‐resolution soil NOX emission inventory and the WRF‐Chem air quality model. We first validate the simulation result of the O3 concentration with surface O3 observations over China using the selected optimal physicochemical scheme. After that, four scenarios are designed to simulate and analyze the regional sensitivity of O3 to soil NOX emissions and to quantify the effect of soil NOX emissions on O3 concentration. The results indicate that as soil NOX emissions increase, the overall spatial pattern does not change notably over mainland China, but the O3 concentration increases remarkably in the northwest and northeast of China. Additionally, we discover that changes of O3 concentration across mainland China differ substantially among regions. Our results highlight the effect of soil NOX emissions on air quality in agricultural areas. The control of O3 pollution in China should take into account the comprehensive consequences of various emission sources, as well as their regional differences. Plain Language Summary: Ozone (O3) is the secondary pollutant in the atmosphere and is harmful to human health. With the management of air pollution in China in the past years, emissions of some pollutants have been controlled with the support of emission control policies, while as photochemical O3 pollution remains serious. In recent years, various methods have been used to resolve regional O3 sources and to investigate the impact of variations in precursor emissions on O3 over China. However, they have mainly concentrated on urban areas, and the emissions of soil NOX have been ignored or simplified in many air quality models for the evaluation of O3 emission control strategies in China. This study uses simulations from the WRF‐Chem model to examine the response of O3 to soil NOX emissions and the impact of soil NOX emissions on O3 concentrations in mainland China and its sub‐regions. The results demonstrated that although soil NOX emissions have little impact on the distribution of O3 sensitivity across China, controlling soil NOX emissions becomes crucial in fighting against O3 pollution in particular areas. Key Points: The simulation results of ozone (O3) concentration are improved by adding soil nitrogen oxides (NOX) emissionsThe sensitivity of O3 to NOX shows a decreasing trend in the fluctuant mixture sensitive areas induced by soil NOX emissionsVariation of soil NOX emissions causes the largest fluctuations in O3 concentrations in the northeast of China [ABSTRACT FROM AUTHOR]

Soil nitrogen oxides (NOx) emissions from agricultural areas currently dominate in some regions around the world. Since China is largely an agricultural country, an accurate estimation of soil NOx emissions from agricultural areas is essential for monitoring air pollution. In this study, we use high‐resolution multi‐source remote sensing data to enhance data inputs to existing empirical NOx emission models, with a particular emphasis on crop phenological features and the impact of nitrogen fertilizer application on NOx at the grid level. As a result, a high‐resolution emission inventory of soil NOx from agricultural areas in China is built. According to the emission inventory, total national NOx emissions from fertilized croplands were 3,741 ± 0.39, 3,231 ± 0.39, and 3,059 ± 0.39 Gg N/yr during 2017–2019, respectively. Moreover, in 2017, soil NOx emissions contributed to 17.3% of the total emissions. It was found the "Hu Huanyong Line" (Hu line) is a dividing line for China's agricultural soil NOx emissions, with soil NOx emissions dominating in the west of the Hu line while being high in the east. The results also show that emissions are highest in summer and lowest in winter, with a significant difference between the two seasons. Furthermore, crop cultivation structure can affect overall soil NOx emissions, which suggests a potential NOx reduction strategy. We demonstrate that the established emission inventory can precisely reflect the distribution of soil NOx emissions in China's agricultural areas, which will be beneficial to overall NOx emission control and air quality improvement. Plain Language Summary: Nitrogen oxides (NOx) are one of the major pollutants in the atmosphere and are harmful to human health. Previously, NOx emission estimates were mainly focused on the industry and transportation sectors. However, as different emission reduction strategies have improved in recent years, some previously ignored emission sources have now gained attention, such as soil NOx emissions from agricultural areas. Meanwhile, practically all of the current estimations of soil NOx emission estimates rarely use high‐resolution remote sensing data sets and seldom take into account crop growth. Therefore, in this study, a high‐resolution soil NOx emission inventory for agricultural areas in China was established based on an empirical model. It highlighted the effects of crop phenology and nitrogen fertilizer application on emissions. The WRF‐Chem model was used to compare the produced emission inventory with Ozone Monitoring Instrument satellite data, and the findings demonstrated that the emission inventory could precisely represent the distribution of soil NOx emissions in agricultural areas of China. As a result, our research output can offer better suggestions for NOx emission control. Key Points: Soil nitrogen oxide (NOx) emissions from fertilized cropland accounted for 17.3% of total NOx emissions in China in 2017Soil NOx emissions are dominating in the west of the "Hu line" in China, although the absolute soil NOx emissions in the east are even higherThe inventory of soil NOx emissions in agricultural areas of China can provide better information for NOx emission control policies [ABSTRACT FROM AUTHOR]

Biogenic volatile organic compounds (BVOCs) simulated by current air quality and climate models still have large uncertainties, which can influence atmosphere chemistry and secondary pollutant formation over East China. These uncertainties are generally resulted from two sources. One is from different biogenic emission schemes coupled in model, representing for different treatments of physical and chemistry progresses during the emissions of BVOCs. The other is from the biased distribution of vegetation types over a specific region. In this study, the version of WRF-Chem updated by the University of Science and Technology of China (USTC version of WRF-Chem) from the public WRF-Chem(v3.6) is used. The modeling results over East China with different versions (v1.0, v2.0, v3.0) of Model of Emissions of Gases and Aerosols from Nature (MEGAN) in WRF-Chem are examined and documented. Sensitivity experiments with these three versions of MEGAN and two vegetation datasets are conducted to investigate the difference of three MEGAN versions in modeling biogenic VOCs and its dependence on the vegetation distributions. The experiments are also conducted for spring (April) and summer (July) to examine the seasonality of the modeling results. The results indicate that MEGANv3.0 simulates the largest amount of biogenic isoprene emissions over East China. The different performance among MEGAN versions is primarily due to their different treatments of applying emission factors and vegetation types. In particular, the results highlight the importance of considering sub-grid vegetation fraction in estimating BVOCs emissions. Among all activity factors, temperature-dependent factor dominates the seasonal change of activity factor in all three versions of MEGAN, while the different response to the leaf area index (LAI) change determines the difference among the three versions in seasonal variation of BVOC emissions. The simulated surface ozone concentration due to BVOCs can be significantly different among the experiments with three versions of MEGAN, which is mainly due to their impacts on surface VOCs and NOx concentrations. This study suggests that there is still large uncertain range in modeling BVOCs and their impacts on photochemistry and ozone production. More accurate vegetation distribution and measurements of biogenic emission flux and species concentration are needed to evaluate the model performance and reduce the uncertainties. [ABSTRACT FROM AUTHOR]