We report that organonitrates were photochemically formed in wet aerosols via aqueous chemistry in the NO_x–O₃ chamber at high humidity. Organonitrates are considered to form in the gas phase (peroxy radical–NO during the daytime or VOC–NO₃ during the nighttime); however, our chamber study results suggest daytime organonitrate formation in polluted and humid areas. Besides organonitrates, organonitrogens, organosulfates, and organonitrogen sulfates were also dominant photooxidation products.