Acidic Deposition: Review of Current Knowledge

摘要

Events in Europe which led to the introduction of the concern for acidic deposition in eastern North America are reviewed. Some of the early conclusions regarding the existence of a trend and the extent of the phenomenon are reexamined. These reexaminations indicate that the definition of a precipitation acidity trend is questionable. Also, it was verified that any explanation of the variability of precipitation acidity must consider such factors as drought and farming and forest management activities. The chemical constituents contributing most to precipitation acidity are reviewed as an indication of primary sources. Sulfate is the primary contributor in the Northeast (60 to 70%). The contribution due to nitrates in this region increased from about 22% in the mid-1950s to about 30% in 1973. However, in other regions deposition acidity may be attributable to a much different combination of chemical species, and may even be dominated by an acidic constituent other than sulfate or nitrate. Several individual processes involved in the transport and transformation of precursor pollutants from source to receptor were briefly reviewed. These processes included mechanisms for the transformation of SO sub 2 and NO/sub x/ emissions into sulfates and nitrates, specific meteorological conditions conducive to long-range transport, major source identification, and the incorporation of this information into mathematical models to predict acidic deposition amounts and patterns. Although the information presented does not explore ecery facet of each process, it does address important governing features and allows for an appreciation of the complexity of quantifying the complete process through use of mathematical models. (ERA citation 08:021690)