Cycling of Gaseous Reactive Nitrogen Oxides and Its Role in Driving Secondary Pollution

Gaseous reactive nitrogen oxides (RNO) are important precursors of photochemical smog, acid rain, and haze. They can be transported and converted at any time of the day. Therefore, we summarize the cycle and conversion of these gaseous RNO species at different times of the day: during the day, during the day-night transition, and at night, respectively. Subsequently, taking into account the complex atmospheric environment, we then analyzed the effects of the VOC photochemistry and temperature on the gas-phase RNO cycle conversion. In addition, we also comprehensively discuss the impact of the gas-phase RNO cycle on the atmospheric oxidizing capacity (O₃, OH radicals and their precursors) as well as on the formation and growth of secondary organic aerosols. Finally, challenges related to the accurate quantification of gaseous RNO species and nitrogen conservation are singled out; urgent future prospects about the accurate assessment of the impact of the RNO cycle on regional atmospheric pollution and global climate change are also highlighted. The aim of this review is to elucidate the key gaseous RNO cycle in the atmosphere and its impact on atmospheric complex pollution and ultimately to provide essential ideas for the deep abatement of reactive RNOs.