Aqueous layer emission sources

Atmospheric pollutants can be deposited into the aqueous layer by either wet or dry deposition. For wet deposition to take place it is necessary for rain, fog, dew, or snow to be present, whereas for dry deposition precipitation of any kind is not involved. Dry deposition is considered to be predominant indoors or in highly polluted areas close to emission sources. It is difficult to determine the relative importance of wet deposition because of the incidental nature of the precipitation. 

The incorporation of atmospheric species into the aqueous layer may occur through either dry or wet deposition. In dry deposition there is no involvement of any precipitation, whereas wet deposition requires, e.g., rain, dew, fog, or snow for atmospheric pollutants to deposit. Indoors or in highly polluted areas close to emission sources, dry deposition is considered to be dominating but the relative importance of wet deposition may be difficult to establish because of the incidental nature of precipitation. Controlled field studies combined with extensive laboratory exposures have been undertaken within the National Acid Precipitation Assessment Program (NAPAP) to explore the relative contribution of wet and dry deposition to increased corrosion rates of a number of metals [45]. 

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