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

Soil nitrogen dioxide (NOX = NO2 + NO) emissions have been measured and estimated to be the second most significant contributor to the NOX burden following the fossil fuel combustion source globally. NOX 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 NOX emission and its contribution to the near-surface ozone (O-3) pollution in North China Plain (NCP) during a growing season as a case study. Model simulations have revealed that the cropland NOX emissions are underestimated by around 80% without constraints of satellite measured NO2 column densities. The biogenic NOX source is estimated to account for half of the anthropogenic NOX emissions in the NCP during the growing season. Additionally, the cropland NOX source contributes around 5.0% of the maximum daily average 8h O-3 concentration and 27.7% of NO2 concentration in the NCP. Our results suggest the agriculture NOX emission exerts non-negligible impacts on the summertime air quality and needs to be considered when designing emission abatement strategies.

Automated summary

Soil NOX emissions, the second largest contributor to global NOX burden after fossil fuel combustion, are often underestimated or overlooked in regional air pollution simulations. Using the WRF-Chem model with ground and satellite observations, this study investigates cropland NOX emissions and their contribution to near-surface ozone pollution in the North China Plain (NCP) during a growing season. Results show that cropland NOX emissions are underestimated by around 80% without satellite constraints, with half of the anthropogenic NOX emissions in the NCP being attributed to biogenic sources during the growing season. Additionally, cropland NOX emissions contribute significantly to the summertime air quality in the NCP.