The transfer of trace species (gases or particles) from the atmosphere to surfaces as a consequence of molecular diffusion, brownian diffusion, or gravitation settling, in the absence of active precipitation. The term refers to the transfer process and not to the surface themselves, which may be moist. [Graedel, T. E. and Paul J. Crutzen. Atmospheric Change: An Earth System Perspective. W. H. Freeman and Company: New York, 1993.]
