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This article in JEQ

  1. Vol. 23 No. 1, p. 180-187
     
    Received: Aug 10, 1992


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doi:10.2134/jeq1994.00472425002300010028x

Nonisothermal Sorption Gaseous Exchange in a Synthetic Soil

  1. S. Goldman * and
  2. L.M. Minkin
  1. Oregon Graduate Inst. of Sci. & Technol., Dep. of Environ. Sci. and Eng., P.O. Box 91000, Portland, OR 97291-1000.

Abstract

Abstract

Nonisothermal sorption on soil surfaces is involved in the exchange of gases between soils and the atmosphere. This process is considered in context of soil pore-size distribution. We found that the gas flux caused by nonisothermal sorption can be significant and can exceed the gas fluxes induced by other physical mechanisms of soil-atmosphere exchange. We investigated the influence of fluctuations of soil temperature on the amount of gas sorbed to soil. For a given soil mass and for a given primary atmospheric gas, the ratio between the moles of gas sorbed or desorbed on a soil surface due to one Kelvin change of soil temperature and the moles of gas initially adsorbed ranges from 0.016 to 0.054 K−1. This temperature dependence, in turn, leads to a significant change of gas concentration in porous media, especially for dry and fine-structured soils and clays. Significant gas fluxes can result. For an upper soil layer with a specific surface area of 2 × 104 m2 kg−1, the CO2 flux induced by nonisothermal sorption equals 8.3 × 10−4 kg m−2 s−1 when the soil temperature changes 1 K h−1 . These sorption processes are considered for soils having different pore-size distributions. In certain fine-structured soils, the number of sorbed molecules in a given soil mass is similar to the number of nonsorbed (mobile) molecules in the porous volume, particularly for gases with enthalpy of adsorption greater than 20 000 J mol−1 K−1. A new type of function is offered for describing pore diameter distribution. This function can be fitted easily to experimental data for many types of soil matrices, and it is also convenient for statistical moment analysis. This concept has been applied to the matrices of Walla-Walla (coarse, silty, mixed, mesic Typic Haploxerolls) and Bashaw soils (very fine, montmorillonitic, mesic Typic Pelloxererts) (Oregon).

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