A process that removes airborne materials from the atmosphere and deposits them on a surface. Dry deposition includes the settling or falling-out of particles due to the influence of gravity. It also includes the deposition of gas-phase compounds and particles too small to be affected by gravity. These materials may be deposited on surfaces due to their solubility with the surface or due to other physical and chemical attractions. Airborne contaminants are removed by both wet deposition, such as rainfall scavenging, and by dry deposition. The sum of wet and dry deposition is called total deposition. Deposition processes are the most important way contaminants such as acidic sulfur compounds are removed from the atmosphere; they are also important because deposition processes transfer contaminants to aquatic and terrestrial ecosystems. Cross-media transfers, such as transfers from air to water, can have adverse environmental impacts, and an example of this is how dry deposition of sulfur and nitrogen compounds can acidify poorly buffered lakes.