ABSTRACT
Measurements of chemical concentrations in the atmosphere, rainfall, lake waters, biota, and sediments have revealed that there is often appreciable transfer of chemicals between the atmosphere and lakes in both direction. The concentrations established in the few metres of air and water adjacent to the interface are thus determined by the rates of the various processes as influenced by partitioning in both phases. Air-water equilibria are normally expressed by a Henry's Law constant or air-water partition coefficient. Methods of characterizing air-water exchange processes quantitatively are best illustrated by a calculation. Chemical which is sorbed to aerosol particles may fall to the water surface and become incorporated into the water column by a process called dry deposition. This process is often viewed as similar to that of a stone falling into water under the action of gravity, but this is a somewhat misleading analogy.
