ABSTRACT
This chapter presents the state of the art on estimating the exchange coefficients between soil and air. The transport processes which occur near the air/soil interface play an important role in regulating chemical movement in this region. Exchange coefficients are needed in modeling efforts aimed at predicting rates of chemical movement to and from the soil. Typical applications in which knowledge of transport rates is important are the vaporization of pesticides from agricultural land, hydrocarbons from petroleum landfarms, chlorinated volatiles from landfill cells, and the dry deposition of oxides of sulfur and nitrogen onto soil surfaces. Mass flow occurs as a result of external forces acting on carriers such as water, air, and soil particles. The solutes may be soluble in or "sorbed" by the carriers and subsequently transported by the carriers. The chapter concludes with recommendations of equations and techniques by which to estimate the coefficients for the benchmark chemicals.
