Daytime Atmospheric Halogen Cycling through Aqueous-Phase Oxygen Atom Chemistry.

Halogen atoms are important atmospheric oxidants that have unidentified daytime sources from photochemical halide oxidation in sea salt aerosols. Here, we show that the photolysis of nitrate in aqueous chloride solutions generates nitryl chloride (ClNO 2 ) in addition to Cl 2 and HOCl. Experimental and modeling evidence suggests that O( 3 P) formed in the minor photolysis channel from nitrate oxidizes chloride to Cl 2 and HOCl, which reacts with nitrite to form ClNO 2 . This chemistry is different than currently accepted mechanisms involving chloride oxidation by OH and could shift our understanding of daytime halogen cycling in the lower atmosphere.