Diffusion of volatile organics through porous snow: impact of surface adsorption and grain boundaries

Abstract

Release of trace gases from surface snow on Earth drives atmospheric chemistry, especially in the polar regions. <br><br> The gas-phase diffusion of methanol and of acetone through the interstitial air of snow was investigated in a well-controlled laboratory study in the temperature range of 223 to 263 K. The aim of this study was to evaluate how the structure of the snowpack, the interaction of the trace gases with the snow surface, and the grain boundaries influence the diffusion on timescales up to 1 h. <br><br> The diffusive loss of these two volatile organics into packed snow samples was measured using a chemical ionization mass spectrometer. The structure of the snow was analyzed by means of X-ray computed micro-tomography. The observed diffusion profiles could be well described based on gas-phase diffusion and the known structure of the snow sample at temperatures &geq; 253 K. At colder temperatures surface interactions start to dominate the diffusive transport. Parameterizing these interactions in terms of adsorption to the solid ice surface, i.e. using temperature dependent air–ice partitioning coefficients, better described the observed diffusion profiles than the use of air–liquid partitioning coefficients. No changes in the diffusive fluxes were observed by increasing the number of grain boundaries in the snow sample by a factor of 7, indicating that for these volatile organic trace gases, uptake into grain boundaries does not play a role on the timescale of diffusion through porous surface snow. <br><br> In conclusion, we have shown that the diffusivity can be predicted when the structure of the snowpack and the partitioning of the trace gas to solid ice is known

Summer variability of the atmospheric NO2 : NO ratio at Dome C on the East Antarctic Plateau

“…Overall, the mean NO 2 : NO ratio was 1.3 ± 1.1 (1σ ) for December and 0.4 ± 0.4 (1σ ) for January. A possible reason for time lag are the different residence times in the porous snow after production, and transport through snow can indeed be slowed due to interaction with the snow interface, (Bartels-Rausch et al, 2013). However, both NO 2 and NO are not adsorbed by snow (Bartels et al, 2002).…”

Direct immersion solid‐phase microextraction with gas chromatography and mass spectrometry for the determination of specific biomarkers of human sweat in melted snow

“…This experiment was carried out to evaluate the applicability of the method in real snow samples and the feasibility of future investigations on the diffusion mechanism of these compounds through the snowpack. In fact, although several studies were carried out to investigate the diffusion mechanism of volatiles through the interstitial air of snow from chemicals present in the atmosphere into the snowpack , the diffusion mechanism of polar volatile compounds that diffuse from the snowpack to the atmosphere, as in the case of avalanche victims, was scarcely ever reported.…”