Nitrate is an important light-absorbing, inorganic ion that is present in aqueous environments including snow and ice following the deposition and reaction of nitrogen reservoir species such as HNO3 or N2O5. Although often thought of as a final sink for nitrogen oxides (NO and NO2), it has recently been shown that nitrate can be photolysed in the snowpack, recycling reservoirs of nitrogen oxides back into the atmosphere and influencing the atmospheric oxidative state. The proximity of nitrate anions to the air-aqueous interface strongly influences their photodissociation quantum yield, due to a reduced solvent cage effect at the air-aqueous surface. Although nitrate in aqueous solution exhibits neutral surface affinity, we have used surface-region sensitive glancing-angle Raman spectroscopy, to show that halide ions in solution increase the propensity of nitrate at the air-aqueous interface. We further investigated this halide enhancement effect on nitrate surface propensity in frozen aqueous solutions containing nitrate and halide ions. Illumination of frozen solutions with artificial sunlight was performed with simultaneous monitoring of the evolution of gas-phase nitrate photolysis products (NO, NO2, NOy) using a 2-channel nitrogen oxide chemiluminescent instrument. Such laboratory chamber studies of frozen nitrate-halides solutions will help parameterize environmental conditions that govern nitrate surface behaviour in snowpacks, its photolysis there, and impacts on atmospheric composition and chemistry.

Nitrate anion surface behaviour and photolysis in frozen aqueous solutions containing nitrate and halide ions

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.