Abstract
Abstract. Sun-lit snow is increasingly recognized as a chemical reactor that plays an active role in uptake, transformation, and release of atmospheric trace gases. Snow is known to influence boundary layer air on a local scale, and given the large global surface coverage of snow may also be significant on regional and global scales. We present a new detailed one-dimensional snow chemistry module that has been coupled to the 1-D atmospheric boundary layer model MISTRA. The new 1-D snow module, which is dynamically coupled to the overlaying atmospheric model, includes heat transport in the snowpack, molecular diffusion, and wind pumping of gases in the interstitial air. The model includes gas phase chemical reactions both in the interstitial air and the atmosphere. Heterogeneous and multiphase chemistry on atmospheric aerosol is considered explicitly. The chemical interaction of interstitial air with snow grains is simulated assuming chemistry in a liquid-like layer (LLL) on the grain surface. The coupled model, referred to as MISTRA-SNOW, was used to investigate snow as the source of nitrogen oxides (NOx) and gas phase reactive bromine in the atmospheric boundary layer in the remote snow covered Arctic (over the Greenland ice sheet) as well as to investigate the link between halogen cycling and ozone depletion that has been observed in interstitial air. The model is validated using data taken 10 June–13 June, 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). The model predicts that reactions involving bromide and nitrate impurities in the surface snow can sustain atmospheric NO and BrO mixing ratios measured at Summit, Greenland during this period.
Highlights
The significance of chemistry in surface snow and on ice was first discussed in the context of boundary layer ozone depletion events in the coastal Arctic during spring (Hausmann and Platt, 1994; Barrie et al, 1988; Foster et al, 2001)
HONO release from the remote snowpack has been measured in the Arctic (Zhou et al, 2001; Dibb et al, 2002; Honrath et al, 2002) and recent model work suggesting HONO is formed from NO−2 on the surface of snow grains, followed by transfer to the interstitial air and mixing upwards via wind pumping was presented by Liao and Tan (2008)
We focused on three days of observations (10 June– 13 June 2008) made during the Greenland Summit Halogen-HOx experiment (GSHOX) experiment at Summit, Greenland in order to test MISTRA-SNOW
Summary
The significance of chemistry in surface snow and on ice was first discussed in the context of boundary layer ozone depletion events in the coastal Arctic during spring (Hausmann and Platt, 1994; Barrie et al, 1988; Foster et al, 2001). Recent laboratory experiments show that OH produced from nitrate at the surface of frozen ice reacts with bromide to form gas phase bromine with high efficiency (Abbatt et al, 2010) This suggests that nitrate is an oxidant that contributes to halogen activation and release at the surface of snow grains. HONO release from the remote snowpack has been measured in the Arctic (Zhou et al, 2001; Dibb et al, 2002; Honrath et al, 2002) and recent model work suggesting HONO is formed from NO−2 on the surface of snow grains, followed by transfer to the interstitial air and mixing upwards via wind pumping was presented by Liao and Tan (2008). We will discuss the impact of halogen chemistry on HOx and model sensitivity to a number of input parameters and environmental conditions including HONO, H2O2 and HOx chemistry (Thomas et al, 2011)
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