Air/soil interface

Considerable work has been done on the behavior of pollutant species at air-water and air-soil interfaces. For example, wet and diy deposition measurements of various gaseous and particulate species have been made over a wide range of atmospheric and land-cover conditions. Still, the problem is of such complexity that species-dependent and particle-size-dependent rates of transfer from the atmosphere to water and soil surfaces are not completely understood. There is much to be learned about pollutant transfer at water-soil interfaces. Concern about groundwater contamination by mineral... 

Partitioning between air/water (including snow), air/plant, and air/soil interfaces (Swackhamer and McConnell 1993)... 

Cousins IT, Beck AJ, Jones KC. 1999. A review of the processes involved in the exchange of semivolatile organic compounds (SVOC) across the air-soil interface. Sci Total Environ 228 5-24. 

The volatilization from soil is more complicated because of the numerous additional mechanisms that are present in the soil, as shown in Figure 7.1. To be volatilized from soil, the herbicide may be lost directly from its solid form to its gaseous form, or it may be released from being adsorbed to soil particles into the soil solution, diffuse into the soil air, and move to the surface to be dispersed into the turbulent air flow above the soil. How close this turbulent region is to the surface depends on the condition of the soil surface. Cultivation practice and soil texture determine the number and size of the clods on the surface, and thus the relative smoothness will determine the evenness of the application of the herbicide and influence the air flow and microclimate at the air-soil interface. The air within the soil is virtually static above this, there is an area of laminar... 

The models are presented in both concentration and fugacity formats. The fugacity format is convenient because at the interface between layers a common fugacity applies whereas there can be differences in concentration, especially at the air-soil interface. This is illustrated in Figure 8.4. 

Mass transfer between soil and air involves diffusion, dry deposition, washout by rain. With one well-mixed soil compartment, the rate of net mass transfer from soil to air is given by 8.12, which contains terms for net gaseous diffusion, dry particle deposition, and transfer in precipitation (rain) to obtain the net flow (FZoWsa, mol d ) across the air-soil interface ... 

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