Diffusion of volatile organics through porous snow: impact of surface adsorption and grain boundaries 1Paul Scherrer Institute, Laboratory of Radio- and Environmental Chemistry, 5232 Villigen PSI, Switzerland
18 Jul 2013
2University of Toronto, Department of Chemistry, Toronto, Ontario M5S 3H6, Canada
3WSL Institute for Snow and Avalanche Research SLF, 7260 Davos Dorf, Switzerland
Received: 01 Feb 2013 – Published in Atmos. Chem. Phys. Discuss.: 07 Mar 2013 Abstract. Release of trace gases from surface snow on earth drives atmospheric
chemistry, especially in the polar regions.
Revised: 17 May 2013 – Accepted: 22 May 2013 – Published: 18 Jul 2013
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. 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 analysed by means of X-ray-computed
The observed diffusion profiles could be well described based on gas-phase
diffusion and the known structure of the snow sample at temperatures
≥ 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. For
this, a snow sample with an artificially high amount of ice grains was
produced and the grain boundary surface measured using thin sections.
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.
Citation: Bartels-Rausch, T., Wren, S. N., Schreiber, S., Riche, F., Schneebeli, M., and Ammann, M.: Diffusion of volatile organics through porous snow: impact of surface adsorption and grain boundaries, Atmos. Chem. Phys., 13, 6727-6739, doi:10.5194/acp-13-6727-2013, 2013.