Light penetration in the snowpack at Summit, Greenland: Part 1

In part 1 of this study, we use this method at Summit, Greenland on the surface snow and to depths of ∼30cm using hydrogen peroxide (HOOH) and nitrite (NO2-) as the chromophores. While the method works well for determining the rate constant for HOOH photolysis (j(HOOH)), we encountered problems using the technique with nitrite. However, measured PhOH formation rate constants for nitrite in acetonitrile, jNO2-→PhOHACN, still provide an excellent means for calculating snowpack e-folding depths for NO2- photolysis (i.e., the depth over which the rate constant decreases by a factor of e). Values of j(HOOH) and j(NO2-) determined from measurements of actinic flux (above the snow) and irradiance (in snow) suggest that the value of j(HOOH) on the surface snow at midday was 8.6×10-7s-1 in mid-March and increased by 300% by the start of May, while jNO2-→PhOHACN midday surface values were consistently (1-3)×10-7s-1 throughout the season. Within the snowpack, average e-folding depths determined from chemical actinometry were 13.3(±0.88)cm for j(HOOH) and 16.3(±4.2)cm for jNO2-→PhOHACN; e-folding depths determined from in-snow spectral radiometer measurements of irradiance were similar. The larger e-folding depth for nitrite is because this chromophore absorbs at longer wavelengths where there is less light extinction in the snow.