Multiphase modeling of nitrate photochemistry in the quasi-liquid layer (QLL): implications for NOx release from the Arctic and coastal Antarctic snowpack

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Boxe, C. S., Saiz-Lopez, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2008
• Subjects: article; Verlagsveröffentlichung; Antarctic; Arctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-8-4855-2008; https://noa.gwlb.de/receive/cop_mods_00048110; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00047730/acp-8-4855-2008.pdf; https://acp.copernicus.org/articles/8/4855/2008/acp-8-4855-2008.pdf

We utilize a multiphase model, CON-AIR (Condensed Phase to Air Transfer Model), to show that the photochemistry of nitrate (NO3−) in and on ice and snow surfaces, specifically the quasi-liquid layer (QLL), can account for NOx volume fluxes, concentrations, and [NO]/[NO2] (γ=[NO]/[NO2]) measured just above the Arctic and coastal Antarctic snowpack. Maximum gas phase NOx volume fluxes, concentrations and γ simulated for spring and summer range from 5.0×104 to 6.4×105 molecules cm−3 s−1, 5.7×108 to 4.8×109 molecules cm−3, and ~0.8 to 2.2, respectively, which are comparable to gas phase NOx volume fluxes, concentrations and γ measured in the field. The model incorporates the appropriate actinic solar spectrum, thereby properly weighting the different rates of photolysis of NO3− and NO2−. This is important since the immediate precursor for NO, for example, NO2−, absorbs at wavelengths longer than nitrate itself. Finally, one-dimensional model simulations indicate that both gas phase boundary layer NO and NO2 exhibit a negative concentration gradient as a function of height although [NO]/[NO2] are approximately constant. This gradient is primarily attributed to gas phase reactions of NOx with halogens oxides (i.e. as BrO and IO), HOx, and hydrocarbons, such as CH3O2.