Corrosion-related aspects of the chemistry and frequency of occurrence of precipitation.

Surfaces exposed to the atmosphere receive water in several forms: adsorption of water vapor, condensation of dew and fog, and deposition of rain and snow. The natural deterioration of wetted materials is enhanced by the corrodents contained in the water as well as by gaseous molecules subsequently incorporated into the water. This paper reviews the chemistry of the different atmospheric precipitation forms, combines those data with typical annual durations of the precipitation forms in four cities (Albuquerque, Los Angeles, Minneapolis - St. Paul, and New York), and deduces the contribution of each precipitation form to annual exposures of materials surfaces to corrodents. A limited assessment for indoor corrodent gases is also included. Among the results of interest are that the nitrate exposure of surfaces appears to be predominantly due to gaseous deposition, that deposition of organic corrodents is as high or higher indoors than it is outside, that materials exposure to the sulfate ion may occur more from dew than from other forms of precipitation, and that under some circumstances fog, rain, and perhaps snow can contribute substantial fractions of corrodent exposure burdens.