What are the major pollutants found in acid rain? How much acid (percentage of total rain) would have to be present in rain for it to be considered: low-acidity rain, medium-acidity rain, and high-acidity rain; and what would be their respective pH levels?There are several major pollutants found in rain. Acidification is primarily caused by sulfuric and nitric acids. Depending on location, a fair bit of neutralization can occur because of the presence of ammonium. Sulfuric acid is primarily a product of the emission of sulfur dioxide (SO2) from utilities which burn coal. Nitric acid (HNO3) is produced as a result of production of nitrogen oxides from high temperature combustion. The source of the nitrogen is primarily the atmosphere -- diatomic elemental nitrogen which makes up about 70% of the air we breathe -- and thus the sources for nitric acid are more diverse but include major inputs from utilities, industry, and automobiles. The sources of ammonia which contribute to the formation of (primarily) ammonium sulfate in rain can be traced to fertilizer, manure, and sewage treatment. This question cannot be answered with strict percentages. It is a function of the type(s) of acidity present -- sulfuric acid, and nitric acid -- but also weak organic acids. It's importance is a function of the surface upon which it falls. Low acidity rain is generally anything above pH 5.0. High acidity rain is somewhere below about pH 4.5. Medium acidity sloshes around somewhere in between. For further research, browse the National Atmospheric Deposition Program web site: http://nadp.sws.uiuc.edu , especially the maps for the past several years. The 1990 National Acid Precipitation Assessment Program State of the Science and Technology documents also provides comprehensive information in it's four volume set. Richard Artz
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