Large contribution of soil emissions to the atmospheric nitrogen budget and their impacts on air quality and temperature rise in North China.

Soil emissions of nitrogen compounds, including NO and HONO, play a significant role in atmospheric nitrogen budget. However, HONO has been overlooked in previous research on soil reactive nitrogen (Nr) emissions and their impacts on air quality in China. This study estimates both soil NO_x and HONO emissions (SNO_x and SHONO) in North China with an updated soil Nr emissions scheme in a chemical transport model, the Unified Inputs for WRF-Chem (UI-WRF-Chem). The effects of soil Nr emissions on O₃ pollution, air quality and temperature rise are also studied, with a focus on two key regions, Beijing-Tianjin-Hebei (BTH) and Fenwei Plain (FWP), known for high soil Nr and anthropogenic emissions. We find that the flux of SNO_x is nearly doubled those of SHONO; the monthly contributions of SNO_x and SHONO account for 37.3 % and 13.5 % of anthropogenic NO_x emissions in the BTH, and 29.2 % and 19.2 % in the FWP during July 2018, respectively. Soil Nr emissions have a significant impact on surface O₃ and nitrate, exceeding SNO_x or SHONO effects alone. On average, soil Nr emissions increase MDA8 O₃ by 16.9 % and nitrate concentrations by 42.4 % in the BTH, 17.2 % for MDA8 O₃ and 42.7 % for nitrate in the FWP. Reducing anthropogenic NO_x emissions leads to a more substantial suppressive effect of soil Nr emissions on O₃ mitigation, particularly in BTH. Soil Nr emissions, via their role as precursors for secondary inorganic aerosols, can result in a slower increase rate of surface air temperature. This study suggests that mitigating O₃ pollution and addressing climate change in China should consider the role of soil Nr emission, and their regional differences. [ABSTRACT FROM AUTHOR]