Fertilization-driven pulses of atmospheric nitrogen dioxide complicate air pollution in early spring over the North China Plain

Abstract. Atmospheric nitrogen dioxide (NO2) has shown periodic conspicuous pulses in the tropospheric column in March over the North China Plain during the past two decades. However, these repetitive pulses have never been reported, and their underlying causes remain unclear. Here, we present robust evidence to demonstrate that agricultural fertilization drives the early spring NO2 column increase. The fertilization-driven soil NOx (= NO+NO2) emissions, comparable to anthropogenic sources, exert complicated influences on regional air quality. They significantly reduce nocturnal and diurnal O3 concentrations in agricultural areas in early spring, distinct from the scenarios in summer, but increase fine particulate matter (PM2.5) concentrations via strongly enhancing nitrate aerosol formation. The impact also extends to urban areas, approximately half that of agricultural areas. These findings have increasing implications for coordinated control of PM2.5 and O3 under global warming. We thus suggest that reducing NOx emissions in croplands is essential to achieve better air quality in agricultural countries and regions.