Abstract
Abstract. A 1-D air-snowpack model of HONO has been developed and constrained by observed chemistry and meteorology data. The 1-D model includes molecular diffusion and mechanical dispersion, windpumping in snow, gas phase to quasi-liquid layer phase HONO transfer and quasi-liquid layer nitrate and interstitial air HONO photolysis. Photolysis of nitrate is important as a dominant HONO source inside the snowpack, however, the observed HONO emission from the snowpack was triggered mainly by the equilibrium between quasi liquid layer nitrite and firn air HONO deep down the snow surface (i.e. 30 cm below snow surface). The high concentration of HONO in the firn air is subsequently transported above the snowpack by diffusion and windpumping. The model uncertainties come mainly from lack of measurements and the interpretation of the QLL properties based on the bulk snow measurements. One critical factor is the ionic strength of QLL nitrite, which is estimated here by the bulk snow pH, nitrite concentration, and QLL to bulk snow volume ratio.
Highlights
Increasing interest has been focused on the measurement of atmospheric nitrous acid (HONO) in the high latitude boundary layer
HONO plays an important role in the atmosphere due to its photo-dissociation by UV radiation into hydroxyl (OH) and nitric oxide (NO) radicals
We see a significant increase of the ratio of the gas phase source versus model profile to have a significant effect on HONO concen- sink but a very limited effect for the HONO vertical distributrations
Summary
Increasing interest has been focused on the measurement of atmospheric nitrous acid (HONO) in the high latitude boundary layer. As a result of poor vertical mixing in the polar lower atmosphere, snow pack emissions of HONO remain confined to a thin layer near the surface, where HONO can give rise to a much greater production of OH radicals in Arctic polar sunrise than previously believed (Domine and Shepson, 2002). The high levels of HONO reported often lead to a dramatic over-prediction of HOx (Davis et al, 2004) and sometimes NOx (Dibb et al, 2004), because these high levels are difficult to reconcile with concurrent measurements of OH, HO2 and NO. These results raised possible missing sinks for HOx and NOx or, alternatively, problems with the HONO measurements
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