Atmospheric deposition is a very important transport process for gases and particles from the atmosphere to the terrestrial and aquatic surfaces. This process is a part of biogeochemical cycling of various chemicals in the Earth system. While emitted to the atmosphere from various natural and anthropogenic sources, gases and particles are transported with air masses and undergo dry and wet deposition from the air to water and land.
After deposition, some of the chemicals are accumulated in the upper layer of soil, while another portion migrates through the terrestrial and aquatic environment.
The primary effect of deposition is a cleansing of the air. Concerning the impact of deposition on various sources, this process can be harmful or beneficial. Deposition of ozone on crops would cause a harmful effect. In the case of deposition of nitrogen compounds, this process can be either beneficial or harmful. On one side, deposition of nitrogen can be regarded as an additional transport of nutrients to plants. While in excess, it may cause eutrophi-cation, for example, in coastal areas, large growth of algae populations, and subsequent oxygen deficiency at the bottom waters. Another example of harmful effects on the environment where deposition plays a role is acidification of precipitation, often called as acid rain.
Gases and particles undergo various physical and chemical transformations during the atmospheric transport and deposition. These transformations have an important impact on fate and behavior in the environment of various chemicals transported on particles or in gas phase. There are various physical, chemical, biological, and meteorological parameters affecting the deposition process. There are also various surface characteristics that affect the magnitude of deposition and its chemical and physical forms.
Various models developed to simulate atmospheric deposition process use mathematical representations of the above-mentioned parameters. Several short-term and long-term measurements have been carried out to verify model simulations and improve our knowledge of the importance of the deposition process in chemical cycling in the environment.
This article describes the atmospheric deposition processes, factors affecting the deposition efficiency, models used to simulate these processes, and measurement networks used to verify the model simulations and assess the deposition amounts of various chemicals. Deposition of gases and particles are each described separately. Dry and wet deposition processes for particles are presented separately.
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