Extinction of UV radiation in Arctic snow at Alert, Canada (82°N)

Extinction of ultraviolet (UV) and visible radiation (300-548 nm) in snowpack is reported for surface snow used in snow-atmosphere exchange experiments during the Polar Sunrise Experiment ALERT 2000 (Canadian Forces Station Alert, Canada). The UV penetration distance is reported as the e-folding depth (the depth over which the monochromatic light irradiance decreases by a factor of e) for 2 nm wavelength intervals. Values in the range 5-6 cm are obtained for a uniform snowpack in the wavelength region between the ozone absorption edge in the UV and green light in the visible. Experimental evidence shows at most a weak dependence of the asymptotic e-folding depth on the solar zenith angle. Comparison of these data to previous studies indicates that the e-folding depths vary greatly between sites, most probably due to variations in impurities at each of the sites. These data imply that approximately 85% of a photochemical reaction occurs in the top 10 cm of snowpack at this site.