Enhanced Soil Emissions of Reactive Nitrogen Gases by Fertilization and Their Impacts on Secondary Air Pollution in Eastern China

Nitrogen fertilizer application is accompanied by intense release of multiple reactive nitrogen (Nr) gases such as nitrous acid (HONO), ammonia (NH₃), and nitric oxide (NO) from the soil, influencing atmospheric chemistry and air pollution. In current emission inventories, postfertilization soil emissions are poorly characterized due to inaccurate identification of fertilization timing and location. Moreover, pre-existing studies predominantly focus on individual Nr gases, and a comprehensive understanding of simultaneously emitted Nr gases from fertilization and their impacts on air quality is still limited. Here, we developed a novel method to identify the dryland fertilization activity based on satellite and reanalysis data sets. Then, we updated a dynamic soil Nr emissions model (WRF-SoilN-Chem) with lab-derived parametrization and applied it to analyze the time- and space-varying Nr emissions and their effects on air quality. It is estimated that the Nr emissions from a typical fertilization event in the Yangtze River Delta (YRD) region increased ozone (O₃) and nitrate concentrations by 2.5 and 18.2%, respectively. HONO and NH₃ emissions jointly enhanced nitrate production via gas-particle partitioning. An accurate representation of fertilization and meteorology-emission-chemistry coupled modeling would greatly improve the understanding of the soil Nr emissions and their impacts on regional air pollution.