MEASUREMENT OF THE SPECIFIC SURFACE-AREA OF SNOW WITH THE NITROGEN ADSORPTION TECHNIQUE

Few data exist for the surface area of snow despite its importance for modeling wet deposition and migration of reversibly deposited contami nants in snow. A method for determining the surface area of snow is de scribed that uses a commercial nitrogen adsorption instrument (Gemini ill 2375, Micromeritics Instruments Inc.). The method uses a sample vi al containing snow and a reference vial containing an equal amount of snow that has been melted and refrozen in order to minimize its surfac e area. The basic quantity measured is the difference in volumes of ni trogen delivered to the sample and reference vials. This volume differ ence must be corrected for the free space difference in the vials befo re the adsorbed volume of nitrogen can he inferred. Two methods for ob taining this correction are discussed, measured, and estimated, and th e results of BET analysis are presented for both types of correction. Fresh snow samples collected in southern Ontario exhibit type II isoth erms with moderate to small BET constant values. Snow surface area ran ges from 0.06 to 0.37 m(2)/g. Comparison with literature data for the dimensions of snow crystals suggests that the BET surface area of snow is comparable to the surface area measured by microscopy techniques.