Cropland nitrogen dioxide emissions and effects on the ozone pollution in the North China plain

Soil nitrogen dioxide (NO_X = NO₂ + NO) emissions have been measured and estimated to be the second most significant contributor to the NO_X burden following the fossil fuel combustion source globally. NO_X emissions from croplands are subject to being underestimated or overlooked in air pollution simulations of regional atmospheric chemistry models. With constraints of ground and space observations of NO₂, the WRF-Chem model is used to investigate the cropland NO_X emission and its contribution to the near-surface ozone (O₃) pollution in North China Plain (NCP) during a growing season as a case study. Model simulations have revealed that the cropland NO_X emissions are underestimated by around 80% without constraints of satellite measured NO₂ column densities. The biogenic NO_X source is estimated to account for half of the anthropogenic NO_X emissions in the NCP during the growing season. Additionally, the cropland NO_X source contributes around 5.0% of the maximum daily average 8h O₃ concentration and 27.7% of NO₂ concentration in the NCP. Our results suggest the agriculture NO_X emission exerts non-negligible impacts on the summertime air quality and needs to be considered when designing emission abatement strategies.