Acid Rain
Precipitation made acidic by sulfur dioxide and nitrogen oxide emissions, which damages ecosystems, buildings, and water quality.
Detailed Explanation
Acid rain is precipitation — rain, snow, fog, or dry deposition — that is made unusually acidic by atmospheric pollution, primarily sulfur dioxide (SO2) and nitrogen oxides (NOx). These pollutants are emitted mainly by coal-fired power plants, industrial facilities, and vehicles. In the atmosphere, SO2 and NOx react with water, oxygen, and other chemicals to form sulfuric acid and nitric acid, which then fall to the ground in precipitation or settle as dry particles. Acid rain became a major environmental concern in the 1970s and 1980s, when its effects on lakes, forests, and buildings in the northeastern United States and Scandinavia drew public attention. Acidified lakes lost fish populations, forests showed leaf damage and reduced growth, and limestone and marble buildings and monuments suffered accelerated erosion. The Clean Air Act Amendments of 1990 addressed acid rain through a cap-and-trade program for SO2 emissions from power plants — one of the most successful market-based environmental programs in history. SO2 emissions from power plants have since declined by more than 90%, and acid rain has diminished significantly. However, the ecological damage from decades of acid deposition continues to affect soils and waterways in some regions. While acid rain is no longer a prominent air quality issue in the US, AirHistory's tracking of SO2 data in city pollutant breakdowns reflects the ongoing legacy and current state of sulfur emissions.
Related Terms
Sulfur Dioxide (SO2)
A pungent gas released by burning sulfur-containing fossil fuels, primarily from power plants and industrial facilities.
Nitrogen Dioxide (NO2)
A reddish-brown gas produced primarily by vehicle engines and power plants that contributes to smog and respiratory problems.
Clean Air Act
The primary federal law governing air quality in the United States, first enacted in 1963 and significantly amended in 1970 and 1990.
Emissions Inventory
A comprehensive accounting of air pollutant emissions from all sources in a geographic area, used for regulation and planning.
Frequently Asked Questions
Precipitation made acidic by sulfur dioxide and nitrogen oxide emissions, which damages ecosystems, buildings, and water quality.
Acid rain is precipitation — rain, snow, fog, or dry deposition — that is made unusually acidic by atmospheric pollution, primarily sulfur dioxide (SO2) and nitrogen oxides (NOx). These pollutants are emitted mainly by coal-fired power plants, industrial facilities, and vehicles. In the atmosphere, SO2 and NOx react with water, oxygen, and other chemicals to form sulfuric acid and nitric acid, which then fall to the ground in precipitation or settle as dry particles.