What is acid rain?
Acid rain is rainfall that has been acidified. Rain is acidified by oxides of sulfur and nitrogen. Acid rain usually has a pH of less than 5.6. Acid rain is formed when pollutants called oxides of sulfur and nitrogen, contained in power plant smoke, factory smoke, and car exhaust, react with the moisture in the atmosphere. Dry deposition, such as soot and ash, sleet, hail, snow, smog and low level ozone are forms that acid rain can take, despite its name.
Acid rain is rain that is more acidic than normal. Sulfur dioxides (SO2) and nitrogen oxides (NOx) produced by the burning of fossil fuels are the major cause of acid rain. SO2 and NOx combine with moisture in the air to form acid rain. Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation’s cultural heritage. For more information, see the Mid-Atlantic Acid Rain Program Page.
Acid rain is any precipitation, rain or snow, that is more acidic than “normal” rain or snow. Acidity of substances is measured on the pH scale. Normal levels for rain and snow have a pH level of 5.5. Anything less than this is considered acidic. In 2000, the lowest pH recorded in the United States was 4.3! When sulfur dioxide and nitrogen dioxide are released into the air from cars or factories, they cause the air to become more acidic. These gases combine with the water vapor to form weak acids that become part of the precipitation. What is the Clean Air Act? The Clean Air Act is a Federal law that sets air quality standards for emissions from area, stationary, and mobile sources. This law states that the U.S. Environmental Protection Agency is authorized to set National Ambient Air Quality Standards (NAAQS) which protect human health and the environment. The Act was was amended in 1977 and then again in 1990. Amendments were made in order to address problems such as acid rain, groun
The term “acid rain” is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. The more accurate term is “acid precipitation.” Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a pH less than 7 are acid, and those with a pH greater than 7 are alkaline (or basic). “Clean” or unpolluted rain has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid. Around Washington, D.C., however, the average rain pH is between 4.2 and 4.4. The extra acidity in rain comes from the reaction of air pollutants, primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). The main sources of these pollutants are vehicles and industrial and power-generating plants. In Washington, the main local sources are cars, trucks, and buses. Acidity in rain is measured by collecting samples of rain and measuri
