5.1 - ENVIRONMENTAL GEOLOGY
ACID RAIN - Acidity, or pH, is measured on a scale which ranges from 0 to 14, with a value of 7 as neutral. Values below 7 are acid, and ordinary rain has a pH of 5.5 to 6.0 because it mixes with carbon dioxide to form carbonic acid. Burning fossil fuels emits carbon-dioxide, nitrogen and sulfur that contribute to even more acidic rain, with pH values as low as 2. Acid rain accelerates chemical weathering and adversely effects plants and animals.