Increasing Contribution of Chlorine Chemistry to Wintertime Ozone Formation Promoted by Enhanced Nitrogen Chemistry

Chlorine (Cl) radicals strongly affect atmospheric oxidation and the fate of pollutants. Despite several observations, the potential impacts of nitrogen chemistry associated with NO₂ on Cl chemistry are poorly understood. Here, we provided direct field evidence that the nitrogen chemistry enhancements triggered by the increased NO₂ drove daytime nitrate (NO₃^-) photolysis and nighttime NO₃-N₂O₅ reactions, significantly promoting the increases in the concentrations of ClNO₂ and Cl₂ after the Chinese Spring Festival. The enhancement in the Cl chemistry facilitated the elevations of both O₃ and atmospheric oxidation capacity during the winter daytime. Our findings highlighted the importance of nitrogen chemistry induced by the increased NO₂ in enhanced Cl chemistry.