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Acid rain production (Source: US Environmental Protection Agency)
Even though sulfur dioxide emissions in the U.S. were reduced 26 percent between 1970 and 1983, and nitrogen oxide emissions were reduced eight percent between 1979 and 1983, the reductions were but a small portion of what has been released since the 1940s.
Acid rain results from automotive emissions of nitrogen oxide and power plant emissions of sulfur dioxide (coal-fired sources). Its effects are degradation of lakes, streams, forests, and even man-made structures. Both the nitric and sulfuric acids (that result when these chemicals combine with rain or other water sources) are strong chemicals, even in dilute form.
A reversal in emissions is taking place only in highly developed nations such as the U.S. More efficient pollution devices on cars and smokestacks are having some effect. One ray of hope for some developing nations, such as China and India, is that they are not using America as their model of a mechanized culture. Automobile use, for example, is actively discouraged, although some predict huge increases in car use in developing countries.
In addition, according to a six-year study by the International Institute for Applied Systems Analysis in Austria, current pollution reduction plans will not be adequate to stop the spread of the effects of acid rain. A computer model, now used by more than 15 countries, indicates that the area of Central Europe now affected by high soil acidity will double in size between 1990 and 2000 and increase four times by 2040; and the forest area now affected by sulfur dioxide will also increase.
Because pollution knows no borders, it may be more cost-effective for Western European nations to invest in pollution controls in the Eastern European countries (even to the extent of reducing some of their own pollution-reduction measures), given that the basic equipment required in Eastern Europe is cheaper than the sophisticated equipment required by the West. If you look at Austria, for example, 90 percent of the sulfur deposited there is from abroad and one third comes from seven Eastern European countries. Trying to improve Austria's internal pollution controls will not have much effect unless the pollution coming in is reduced.
In 1970, the U.S. Congress imposed acid emission regulations through the Clean Air Act, strengthened two decades later in 1990. By the 2000s, sulfate and nitrate in precipitation had decreased by some 40 percent. The reason for the was that in the 1950s midwest coal plants spewed sulfur dioxide and nitrogen oxides into the air, turning clouds—and rainfall—acidic, and this poisoned the air and the lakes and the trees and killed fish—mostly in the northeast U.S.
Researchers at Hubbard Brook have continued to study the effects of acid rain on forest growth and on soil and stream chemistry.
Long-term biogeochemical measurements, for example, have documented a decline in calcium levels in soils and plants over the past 40 years. Calcium is leaching from soils that nourish trees such as maples. The loss is primarily related to the effects of acid rain (and acid snow).
The acid rain implications for forests and streams and for humans depending on them are severe
Now, Hubbard Brook’s Long Term Ecological Research scientists have discovered that a combination of today's higher atmospheric carbon dioxide (CO2) level and its atmospheric fallout is altering the hydrology and water quality of forested watersheds—in much the same way as acid rain.
"It's taken years for New England forests, lakes and streams to recover from the acidification caused by atmospheric pollution," says Saran Twombly, National Science Foundation's program director for long-term ecological research.
"It appears that these forests and streams are under threat again. Climate change will likely return them to an acidified state. The implications for these environments, and for humans depending on them, are severe." (Source: Acid Rain: Scourge of the Past or Trend of the Present?)
Acid rain does not—as far as we have been able to determine—directly affect human health. The acid in the rainwater is too dilute to have direct adverse effects. However, the particulates responsible for acid rain (sulfur dioxide and nitrogen oxides) do have an adverse effect. Increased amounts of fine particulate matter in the air do contribute to heart and lung problems including asthma and bronchitis. (Source: “Effects of Acid Rain – Human Health” from epa.gov)
The acid rain implications for forests and streams and for humans, fish, and wildlife depending on them are severe