Measurements of nitrogen oxides from Hudson Bay: Implications for NOx release from snow and ice covered surfaces

Measurements of NO and NO2 were made at a surface site (55.28 °N, 77.77 °W) near Kuujjuarapik, Canada during February and March 2008. NOx mixing ratios ranged from near zero to 350 pptv with emission from snow believed to be the dominant source. The amount of NOx was observed to be dependent on the terrain over which the airmass has passed before reaching the measurement site. The 24 h average NOx emission rates necessary to reproduce observations were calculated using a zero-dimensional box model giving rates ranging from 6.9 × 108 molecule cm−2 s−1 to 1.2 × 109 molecule cm−2 s−1 for trajectories over land and from 3.8 × 108 molecule cm−2 s−1 to 6.6 × 108 molecule cm−2 s−1 for trajectories over sea ice. These emissions are higher than those suggested by previous studies and indicate the importance of lower latitude snowpack emissions. The difference in emission rate for the two types of snow cover shows the importance of snow depth and underlying surface type for the emission potential of snow-covered areas.