Library Index » Science Encyclopedia » Acid Rain - What Is Acid Rain?, Sources Of Sulfate And Nitrate In The Atmosphere, Natural Factors That Affect Acid Rain Deposition

Acid Rain - Sources Of Sulfate And Nitrate In The Atmosphere

emissions natural percent nitrogen

Natural Sources

Natural sources of sulfate in the atmosphere include ocean spray, volcanic emissions, and readily oxidized hydrogen sulfide released from the decomposition of organic matter found in the Earth. Natural sources of nitrogen or nitrates include NO5 produced by microorganisms in soils, by lightning during thunderstorms, and by forest fires. Scientists generally speculate that one-third of the sulfur and nitrogen emissions in the United States comes from these natural sources (this is a rough estimate as there is no way to measure natural emissions as opposed to those that are manmade.)

Sources Caused by Human Activity

The primary anthropogenic (human-caused) contributors to acid rain are SO2 and NO5, resulting from the burning of fossil fuels, such as coal, oil, and natural gas.

Origins of acid rain

Figure 5.15 in Chapter 5 shows the breakdown of U.S. SO2 emissions by source from 1983 to 2002. Fuel combustion by fossil-fueled electric utilities historically has been by far the greatest source of these emissions, accounting for 85 percent of them in 2002. Lesser sources included transportation vehicles and industrial processes.

NO5 emission sources are shown in Figure 5.6 in Chapter 5. Transportation vehicles are the primary source, accounting for 56 percent of the total in 2002. Fuel combustion in power plants is another major source, accounting for 37 percent of the total. Emissions by industry and miscellaneous sources (for example, agriculture) accounted for only 7 percent of the total. Agricultural emissions of nitrogen compounds are due to windblown fertilizers.

Nitrogen pollution of waters has historically been blamed on surface runoff from fertilizer, animal waste, sewage, and industrial waste. Although these are still significant causes, scientists have come to believe that airborne nitrates account for one-fourth of all nitrogen, the second most prevalent cause after fertilizers. Scientists also blame ammonia emissions, which come largely from agricultural activities such as manure handling and fertilizing, for contributing to acid rain. According to the U.S. Geological Survey (USGS), ammonium levels in precipitation increased throughout the 1990s across most of the country. The average increase was 24 percent.

The potential hydrogen (pH) scale

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