Our research investigated nitrate formation in air pollution across inland and coastal cities in northern China during the winters of 2013 and 2018. Using air quality models and isotopic analysis, we identified regional differences, with coastal cities showing more contribution from the dinitrogen pentoxide (N₂O₅) heterogeneous reaction. Reducing nitrogen oxides (NO_x), volatile organic compounds (VOCs), and ammonia (NH₃) was crucial for lowering nitrate levels and improving air quality.