From Glossary of Meteorology
Processes by which traces gases or particles are transferred from the atmosphere to the surface of the earth.
Atmospheric deposition is usually divided into two categories, wet deposition and dry deposition, depending on the phase of the material during the deposition process. Thus, in wet deposition, the gas or particle is first incorporated into a droplet and is then transferred to the surface via precipitation. In dry deposition, the gas or particle is transported to ground level, where it is adsorbed onto a surface. The surface can be the ocean, soil, vegetation, buildings, etc. Note that the surface involved in the dry deposition may be wet or dry—the "dry" in dry deposition refers only to the phase of the material being deposited.