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 NO ₂ on Cl chemistry are poorly understood. Here, we provided direct field evidence that the nitrogen chemistry enhancements triggered by the increased NO ₂ drove daytime nitrate (NO ₃ ^- ) photolysis and nighttime NO ₃ -N ₂ O ₅ reactions, significantly promoting the increases in the concentrations of ClNO ₂ and Cl ₂ after the Chinese Spring Festival. The enhancement in the Cl chemistry facilitated the elevations of both O ₃ and atmospheric oxidation capacity during the winter daytime. Our findings highlighted the importance of nitrogen chemistry induced by the increased NO ₂ in enhanced Cl chemistry.