Nitrate Photolysis in Salty Snow
Karen J Morenz1, Qianwen Shi1, Jennifer G Murphy1
1Department of Chemistry and ‡Department of Physical and Environmental Sciences, University of Toronto , 80 Saint George Street, Toronto, Ontario M5S 3H6, Canada.
The Journal of Physical Chemistry. A
|September 23, 2016
Summary
Snow nitrate photolysis releases nitrogen oxides, impacting atmospheric chemistry. Salt concentration influences these emissions, with low salt enhancing nitrogen dioxide (NO2) release, potentially affecting polar atmospheric oxidative capacity.
Area of Science:
- Atmospheric Chemistry
- Snow Science
- Environmental Chemistry
Background:
- Nitrate photolysis in snow significantly affects atmospheric oxidative capacity.
- Factors controlling the release of gaseous products from snow nitrate photolysis are not fully understood.
Purpose of the Study:
- To investigate how nitrate and salt concentrations influence nitrogen oxide (NO, NO2, NOx) emissions from illuminated snow.
- To understand the relationship between brine composition and gas-phase product release.
Main Methods:
- Systematic study of gas-phase product emissions (NO, NO2, NOx) from illuminated snow samples.
- Varying nitrate and salt (NaCl, Instant Ocean) concentrations in frozen solutions.
- Measuring steady-state release rates of nitrogen oxides.
Main Results:
- Gas-phase nitrogen oxide release correlates with the predicted nitrate concentration in the snow crystal brine.
- Increasing salt concentration generally decreases steady-state nitrogen oxide emissions.
- Low concentrations of NaCl (≤25 mM) enhanced NO2 production by up to 42%, and Instant Ocean (≤200 mM Cl-) by up to 89%.
Conclusions:
- Snow nitrate photolysis is a source of atmospheric nitrogen oxides.
- Salt concentration critically modulates these emissions, with potential implications for polar atmospheric chemistry.
- The observed enhancement of NO2 at low salt levels is a key finding for polar regions.
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