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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 111,
G03004,
doi:10.1029/2006JG000163,
2006
Advective transport of CO2 in permeable media induced by atmospheric pressure fluctuations: 1. An analytical model
W. J. Massman
Rocky Mountain Research Station, USDA Forest Service, Fort Collins, Colorado, USA
Abstract
Advective flows within soils and snowpacks caused by pressure fluctuations at the upper surface of either medium can significantly
influence the exchange rate of many trace gases from the underlying substrate to the atmosphere. Given the importance of many
of these trace gases in understanding biogeochemical cycling and global change, it is crucial to quantify (as much as possible)
any impact these flows can have on the transport of these gases. This study (part 1 of 2) details a new model describing the
influence that naturally occurring, pressure-driven, oscillatory advective flows have on CO2 profiles within soils and snowpacks and on the associated CO2 fluxes emanating from the underlying source. This model, which consists of two layers with differing permeability and CO2 source strength, is developed for both a dispersive and a nondispersive medium. The pressure forcing and the CO2 response, modeled as plane waves in time and the horizontal direction, have amplitudes that vary in the vertical direction
as described by analytical solutions to the diffusion equation (for pressure) and the advective-diffusive and dispersive-diffusive
equations (for CO2). In the case of a dispersive medium, the dispersion coefficient is derived in terms of the horizontal wave number and amplitude
of the pressure forcing at the upper surface and the vertical structure and dispersivity of the medium. Diffusive flux enhancement
factors, developed for the dispersive and nondispersive models, are expressed as functions of the surface amplitude of the
pressure forcing, the permeability and cross-sectional shape and dimension of the pore tubes of the medium, and the vertical
structure of the medium. Results indicate that advective flows induced by naturally occurring atmospheric pressure fluctuations
are likely to enhance diffusive fluxes more in a dispersive medium than a nondispersive medium. However, such pressure forcing
can significantly enhance diffusive fluxes in either medium.
Received 13
January
2006;
accepted 18
May
2006;
published 28
July
2006.
Keywords: soil;
snowpack;
diffusion;
dispersivity;
oscillatory flow;
concentration profiles.
Index Terms: 0426 Biogeosciences: Biosphere/atmosphere interactions (0315); 0466 Biogeosciences: Modeling; 0428 Biogeosciences: Carbon cycling (4806); 0736 Cryosphere: Snow (1827, 1863).
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Citation: Massman, W. J.
(2006),
Advective transport of CO2 in permeable media induced by atmospheric pressure fluctuations: 1. An analytical model,
J. Geophys. Res.,
111,
G03004,
doi:10.1029/2006JG000163.
This paper is not subject to U.S. copyright. Published in 2006 by the
American Geophysical Union.
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