Evolution of the surface area of a snow layer

Atmospheric trace gases can partition between the atmosphere and the snow surface. Quantifying this partitioning requires the knowledge of the surface area (SA) of snow. Eleven samples were taken from a 50 cm thick snow fall at Col de Forte, near Grenoble (French Alps) between January 20 and February 4, 1998. Fresh snow and 3, 8, and 15 day-old snaw were sampled at three different depths. Surface hear, formed after the fall, was also sampled. Air and surface snow temperature, snow density, and snow fall rate were measured. Snow temperature always remained below freezing. Snow SA was measured using methane adsorption at 77.15 K. Values ranged from 2.25 m(2)/g for fresh snow to 0.25 m(2)/g for surface hear and surface snow after 15 days. These values are much too high to be explained by the macroscopic aspect of snow crystals, and microstructures such as small rime droplets must have been present Large decrease in SA with time were observed. The first meter of snowpack had a total surface area of about 50 000 m(2) per m(2) of ground. Reduction in SA will lead to the emission of adsorbed species by the snowpack, with possible considerable increase in atmospheric concentrations.