Enhanced photodegradation of dimethoxybenzene isomers in/on ice compared to in aqueous solution

Abstract. Photochemical reactions of contaminants in snow and ice can be important sinks for organic inorganic compounds deposited onto from the atmosphere sources photoproducts released snowpacks into atmosphere. Snow found bulk matrix, internal liquid-like regions (LLRs), or quasi-liquid layers (QLLs) at air–ice interface, where they readily exchange with firn air. Some studies have reported that direct photochemical occur faster LLRs QLLs than aqueous solution, while others similar rates. Here, we measure photodegradation rate constants loss three dimethoxybenzene isomers under varying experimental conditions, including LLRs, interface nature-identical snow. Relative to find modest enhancements (3- 6-fold) two larger (15- 30-fold) all isomers. We use computational modeling assess impact light absorbance changes on interface. small (2–5 nm) bathochromic (red) shifts relative which increases absorption, but this factor only accounts less 50 % measured constant enhancements. The major responsible appears more efficient photodecay: estimated quantum yields are 6- 24-fold compared solution account majority (51 %–96 %) observed Using a hypothetical model compound an assumed Gaussian-shaped peak, shift peak higher lower wavelengths minor substantial photodecay constants, depending original location magnitude shift. Changes other properties such as width height (i.e., molar absorption coefficient), also rates photodecay. Our results suggest our current understanding processes underestimates some broken down, well release