Acid Rain

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Caused by air pollution, acid rain refers to any kind of acid precipitation such as acid fog, acid sleet, acid snow, acid mist, or any other acidic particles or aerosols that fall to the ground or remain suspended in the atmosphere. The main components responsible for the acidity of these particles are oxides of sulfur and nitrogen that are dissolved in water and deposited on the surfaces of suspended particles. Acid rain has a detrimental effect on human and animal health, endangers plant and marine life, and also degrades materials. The health problems associated with acid rain include lung diseases and respiratory ailments. Its primary effect on plants is the leaching and blocking of the uptake of nutrients and essential minerals, such as calcium and magnesium, from the plants’ roots. Acids are also highly corrosive and attack metals and other construction materials.

The measure of the acidity of a solution is its pH value. The pH scale ranges between 0 and 14. Pure water has a pH of 7 and is considered to be neutral. Acids have pH values lower than 7, and alkalines have pH values higher than 7. The lower the number, the more acidic the substance is. The scale is logarithmic, which means a drop of one in the pH level represents a tenfold increase in the acidity. Thus a pH of 6 is 10 times more acidic than water; the pH of 5 is 100 times more acidic. Even unpolluted rainfall is normally slightly acidic, with a pH of around 5.6, because it includes dissolved carbon dioxides. Precipitation with a lower pH than this is considered acid rain.

Acid rain affects lakes and ponds in an adverse way. The severity of the problem depends on the nature of the lake. In some parts of the world, lakes are in limestone (calcium carbonate), which neutralizes acid. The tendency to neutralize acid provides a buffer against acid rain. In other parts, including the northern US, Canada, and most of Europe, lakes are in granite and have less buffering capacity. Therefore, acid rain poses a greater threat to fish, salamanders, and frogs in these areas. At higher levels of acidity, bacteria and water plants also die. Under these conditions, lake water looks pure, while a healthy lake might have cloudy water because of the natural plant life in it. To increase the alkalinity of the soil and water, some people have proposed liming them; however, this process has proven prohibitively expensive.

Many nations have enacted laws to limit their sulfur emission, mainly by installing scrubbers. Scrubbers remove sulfur dioxide by spraying powerplants’ exhausts with a watery, limestone mist to produce sludge that can be dumped or used to make boards suitable for home building. (Moore)


(1) Moore, Curtis, “Green Revolution in the Marketing,” January/February issue of Sierra.

(2) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Gore, A., An Inconvenient Truth, Penguin Books, 2007.

Roleff, T., Pollution: Opposing viewpoints, Greenhaven Press, 2000.

Walsh, P. J., Dudney, C. S., Copenhave, E. D., Indoor Air Quality, CRC Press, 1984.

Environmental Science and Technology, published by the American Chemical Society.

External Links

Environmental Protection Agency (

Occupational Safety and Health Administration (OSHA) (

Intergovernmental Panel on Climate Control (IPCC), (

United Nations Environment Programme (

World Health Organization (WHO) (