Essay About Effects Of Acid Deposition And S02

Air Pollution
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Acidification is one of the most serious environmental problems. Among the
effects of acid deposition, corrosion of constructions exposed to the atmosphere,
mainly by sulfur pollutants, is a well-known problem. The effects of
S02 on different materials have been subject to many laboratory and field
investigations, and the corrosive effects of polluted atmospheres on historic
and cultural monuments of sandstone or limestone are obvious. Current
knowledge of the effects of acidic air pollutants on atmospheric corrosion
is summarized in several reports (Swedish Ministry of Agriculture, 1982;
United Nations, 1984; Feenstra, 1984, Lanting and Moree, 1984). Among the parameters determining corrosion rate are the presence of a
moisture film on the surface and the pollutant content of this film. Relative
humidity, rain, dew, and temperature are determinants of the so-called time
of wetness, often defined as time with relative humidity> 80% at temperatures
> 0 oc. If mean values for time of wetness and temperature vary only
moderately, which is usually the case in the temperate climatic zone, then
the levels of air pollutants influence the corrosion rate decisively. In very
cold or dry regions, however, the time of wetness becomes a significant parameter.
The influence of high relative humidity and temperature, as found
in the tropics, is treated in a separate chapter.
The major pollutants, in urban and industrial areas are S02 and NOx;
chlorides are usually the dominant pollutant in marine regions. Most of the sulfur from burning fossil fuels is emitted as S02. During its
transport in the atmosphere S02 is oxidized to sulfuric acid in water droplets
or on moist particles. The sulfuric acid can then be partly neutralized by
ammonia to different forms of acid ammonium sulfates such as NH4HS04
and (NH4hH(S04h.
Dry deposition near emission sources in urban and industrial areas consists
largely of adsorption of S02 on surfaces, with the deposited amount
proportional to the content in air. The deposition rate is high at elevated
humidities, especially on some metals; e.g., steel and zinc (Sydberger