Abstract
Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO2), chloroform (CHCl3), dimethylsulfide (CH3)2S, carbondisulfide (CS2), and dichlorobromomethane (CHBrCl2), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH3Cl), methylbromide (CH3Br), dibromomethane (CH2Br2), bromoform (CHBr3), tetrachloromethane (CCl4), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.
Highlights
Gas exchanges between snow and the atmosphere have been receiving increasing research attention
The snowpack sampling technique and resulting concentration gradient measurements from this study proved to be a highly sensitive method for elucidating soil-snow-atmosphere gas exchange processes
Gas diffusivity within the snowpack is significantly slower than above the surface, which results in chemical snowpack concentration gradients that can be well resolved with available analytical techniques
Summary
Gas exchanges between snow and the atmosphere have been receiving increasing research attention. This interest is driven by new evidence that supports the important influence of snow chemistry and physics on surface exchanges, atmospheric processes, and soil biogeochemistry underneath the snowpack. 2. Contaminants can be deposited from the gas phase to snow on the ground by dry deposition. Contaminants can be deposited from the gas phase to snow on the ground by dry deposition This process causes increased levels of trace constituents in the snow as the snowpack ages and has been found responsible for increased levels of many persistent organic pollutants in the arctic environment (Blais et al 1998)
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