Acid Rain
Acid rain occurs when polluting gasses become trapped in clouds that drift for hundreds, even thousands, of miles and are finally released as acidic precipitation. Trees, lakes, animals, and even buildings are vulnerable to the slow corrosive effects of acid rain, whose damaging components are emitted by power plants and factories burning low grades of coal and oil.
Acid rain was first recognized in 1872, approximately one hundred years after the beginning of the Industrial Revolution, when an English scientist, Robert Angus Smith (1817-1884), pointed out the problem. Almost another century passed, however, before the public became aware of the damaging effects of acid rain. In 1962, the Swedish scientist Svante Oden brought the acid rain quandary to the attention of the press, instead of the less popular scientific journals. He compiled records from the 1950s indicating that acid rain came from air masses moving out of central and western Europe into Scandinavia.
After acid rain was detected in Europe, scientists began measuring the acidity of rain in North America. Initially, they found that the problem was concentrated in the northeastern states of New York and Pennsylvania because the type of coal burned there was more sulfuric. But by 1980, most of the states east of the Mississippi, as well as southeastern Canada, were receiving acidic rainfall. Acid rain falls in the West also, although the problem is not as severe. Acid rain in Los Angeles, California is caused primarily by cars.
The prime culprits that create acid rain are sulfur dioxide, nitrogen oxides, and volatile organic compounds (VOCs) such as the vapors from gasoline, industrial chemicals such as benzene, tetrachloroethylene, and some solvents. Sulfur dioxide comes primarily from large utility and industrial sources. Car emissions contain nitrogen oxide, the second highest problematic gas in acid rain after sulfur dioxide. VOCs also come from industrial processes, but smaller amounts can come from vegetation. There is some natural amounts of these compounds in the atmosphere, estimated to be 1 to 5% for sulfur dioxide and 11% for nitrogen oxides.
Acid rain is measured through pH tests which determine the concentration of hydrogen ions. Pure water has a neutral pH of 7. When the pH is greater than 7, the material is said to be alkaline, or basic; acids have a pH less than 7. At a natural pH of 5.7, pure rain has a little bit of acid due to its mixture with naturally-evolving carbon dioxide in the atmosphere, but when its pH is further reduced, the rain becomes pollution. In the worst cases, acid rain has shown a pH of 2.4, which is as acidic as vinegar. When pH levels are drastically tipped in soil and water, entire lakes and forests are jeopardized. Evergreen trees in high elevations are especially vulnerable. Although the acid rain itself does not kill the trees, it makes them more susceptible to other dangers and stresses. Plants and trees that are exposed to acid rain are less effective at photosynthesis and respiration. Also, high acid levels in soil causes leaching, or removal, of other valuable minerals such as calcium, magnesium, and potassium. According to the World Watch Institute, in 1988 forest damage in Europe ranged from a low of 4% in Portugal to a high of 71% in Czechoslovakia, averaging 35% overall.
Small marine organisms cannot survive in acidic lakes and rivers, and their depletion affects larger fish and ultimately the entire marine life food chain. Snow from acid rain is also damaging; snowmelt has been known to cause massive, instant death for many kinds of fish. Some lakes in Scandinavia, in fact, are completely devoid of fish life. Land-based animals also suffer from the effects of acid rain, as do others animals in their food chain. For example, the shells of eggs produced by songbirds in the Netherlands have been found to be defectively thinner--between 30% and 50% of the female birds suffer a calcium deficiency which has been traced to the decline in the population of snails, whose shells the birds eat for its calcium. The snails get calcium from plants, which absorb it from the soil--but acid rain has leached calcium out of the ground and into streams, rivers, and ultimately the ocean. The songbirds' porous shells either bread or dry out, and some chicks that do hatch have bone malformations from a lack of calcium.
Acid rain also eats away at buildings and metal structures. From the Parthenon in Greece to Renaissance buildings in Italy, ancient structures are showing signs of corrosion from acid rain. Also, in some industrialized parts of Poland, trains cannot exceed 40 miles (65 km) per hour because the iron railway tracks have been weakened from acidic air pollution.
Although exact sources of acid rain are difficult to pinpoint, strategies to reduce acid rain levels are being adopted everywhere. New power plants in the United States are being built with strict emissions standards, but retrofitting older plants is difficult and expensive. Nevertheless, the Environmental Protection Agency requires most of the older and dirtier power plants to install electrostatic precipitators and baghouse filters, devices that remove solid particulates. Such devices are required in virtually all of the industrialized countries, such as Japan, Canada, and those of western Europe. Scrubbers, or flue-gas desulfurization technology, are also being used because of their effectiveness in removing as much as 95 percent of a power plant 's sulfur dioxide emissions. These devices are expensive, however, and as of January 1987, only 20 percent of the United States' coal-fired power plants had been equipped with scrubbers, although in Japan 85 percent of the coal-fired power plants were equipped with the device.
Another way to reduce acid rain is for power plants to burn cleaner coal in their plants. This does not require retrofitting but it does increase transportation costs since coal containing less sulfur is mined in the western part of the United States, far away from where it is needed in the mid-west and eastern part of the country.
The National Acid Precipitation Program (NAPAP) has played an important role in the analysis of the acid rain program. Created by the United States Congress in 1980, it spend $500 million over the next ten years to assess the extent of the acid rain problem, and involved thousands of researchers.
The NAPAP report concluded that the amounts of sulfur dioxide and VOCs in the atmosphere in 1990 were "considerably lower than at their peak (in the early 1970s)", but about twice as high as 1900. The United State's Clean Air Act of 1970 was credited for reductions of about 30% for sulfur dioxide and VOCs. Nitrous oxides--virtually absent in the atmosphere in 1900--had also declined from their 1970 highs, thought not as much.
Reactions to this important report were mixed. Environmentalists said it showed there was still too much human contribution to the acid rain problem, and that more efforts to stop pollution were needed. Others, often producers of the problematic compounds, claimed that existing measures were sufficient, since the report showed that the acid rain problem was declining since 1970. Congress passed amendments to the Clean Air Act in 1990, and reauthorized NAPAP and its work.
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