7.7 Acid Rain

What causes acid rain

Acid rain forms when sulfur dioxide (SO2) and nitrogen oxides (NOx) are released from burning fossil fuels (power plants, vehicles) and react with water, oxygen, and other chemicals in the atmosphere to form sulfuric acid (H2SO4) and nitric acid (HNO3). These acids fall as precipitation, lowering pH below the normal ~5.6.

Effects on ecosystems

Acid rain lowers the pH of soil and water, leaching essential nutrients like calcium and releasing toxic aluminum, harming plant roots and aquatic life (especially fish eggs and amphibians). It damages forests, reduces biodiversity in lakes, and corrodes buildings, statues, and infrastructure made of limestone or marble.

Reducing acid rain

Solutions include scrubbers on smokestacks to remove SO2, catalytic converters to reduce NOx from vehicles, switching to low-sulfur fuels or renewable energy, and international regulations like the Clean Air Act. Liming lakes and soils can temporarily neutralize acidity but doesn't address the root cause.

Key terms

Acid rain

Precipitation with abnormally low pH caused by SO2 and NOx reacting with atmospheric water to form sulfuric and nitric acids.

Main sources of SO2 and NOx

Burning fossil fuels in power plants and vehicles.

Scrubber

A device on smokestacks that removes sulfur dioxide before it's released into the air.

Effect of acid rain on soil

Leaches essential nutrients (like calcium) and releases toxic aluminum, harming plant roots.

Effect of acid rain on stone structures

Reacts with calcium carbonate in limestone/marble, causing erosion and damage over time.

Try an AP-style question

Which pollutants cause acid rain?

1. SO₂ and NOx
2. CFCs and lead
3. Ozone and radon
4. CO₂ and methane