Parahalogenated Phenols Accelerate the Photochemical Release of Nitrogen Oxides from Frozen Solutions Containing Nitrate

The photolysis of nitrate anion (NO3 –) contained in surface ice and snow can be a regionally significant source of gas-phase nitrogen oxides and affect the composition of the planetary boundary layer. In this study, the photochemical release of nitrogen oxides from frozen solutions containing NO3 – in the presence of organic compounds was investigated. Gas-phase nitrogen oxides were quantified primarily by NO–O3 chemiluminescence detection of NO and NO y (=NO + NO2 + HONO + HNO3 + ∑PAN + ∑AN ...) and cavity ring-down spectroscopy of NO2 and total alkyl nitrates (∑AN). The photochemical production of gas-phase NO y was suppressed by the presence of formate, methanesulfonate, toluene, or phenol. In contrast, para-halogenated phenols (in the order of Cl > Br > F) promoted the conversion of NO3 – to gas-phase NO y , rationalized by acidification of the ice surface.