Acid rain

Science

Definition

Acid rain is precipitation with a pH below 5.6, caused primarily by sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) released from burning fossil fuels reacting with water vapor in the atmosphere to form sulfuric and nitric acids. It damages ecosystems, buildings, and water sources.

Examples

  • Acid rain has damaged marble statues and limestone buildings across Europe, including the Parthenon
  • Lakes in the Adirondack Mountains became too acidic for fish due to acid rain in the 20th century
  • The U.S. Clean Air Act amendments of 1990 significantly reduced acid rain by capping SO₂ emissions from power plants
Key Fact

Normal rain pH ≈ 5.6 (due to dissolved CO₂); acid rain pH < 5.6, often around 4.2–4.4.

Related Terms

Ph scale Fossil fuels Climate change Water pollution

Study This Concept

Practice acid rain with free review games in these units:

AP Environmental Science Unit 7: Atmospheric Pollution