Measuring the specific surface area of snow with X-ray tomography and gas adsorption: comparison and implications for surface smoothness M. Kerbrat2, B. Pinzer1, T. Huthwelker2, H. W. Gäggeler2,3, M. Ammann2, and M. Schneebeli1 1WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, Davos, Switzerland 2Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 3University of Berne, 3012 Bern, Switzerland
Abstract. Chemical and physical processes, such as heterogeneous chemical
reactions, light scattering, and metamorphism occur in the natural
snowpack. To model these processes in the snowpack, the specific
surface area (SSA) is a key parameter. In this study, two methods,
computed tomography and methane adsorption, which have intrinsically
different effective resolutions – molecular and 30 μm,
respectively – were used to determine the SSA of similar natural
snow samples. Except for very fresh snow, the two methods give
identical results, with an uncertainty of 3%. This implies that the
surface of aged natural snow is smooth up to a scale of about
30 μm and that if smaller structures are present they do
not contribute significantly to the overall SSA. It furthermore
implies that for optical methods a voxel size of 10 μm
is sufficient to capture all structural features of this type of
snow; however, fresh precipitation appears to contain small features
that cause an under-estimation of SSA with tomography at this
resolution. The methane adsorption method is therefore superior to
computed tomography for very fresh snow having high SSA.
Nonetheless, in addition to SSA determination, tomography provides
full geometric information about the ice matrix. It can also be
advantageously used to investigate layered snow packs, as it allows
measuring SSA in layers of less than 1 mm.
Citation: Kerbrat, M., Pinzer, B., Huthwelker, T., Gäggeler, H. W., Ammann, M., and Schneebeli, M.: Measuring the specific surface area of snow with X-ray tomography and gas adsorption: comparison and implications for surface smoothness, Atmos. Chem. Phys., 8, 1261-1275, doi:10.5194/acp-8-1261-2008, 2008.