"Acid rain" is rain (or any other kind of precipitation) that is abnormally acidic.
The acid in acid rain comes from sulphur and nitrogen oxides – air pollutants emitted by (among other sources) motor vehicle exhaust and coal combustion. These pollutants combine with water vapour in the atmosphere to form sulphuric and nitric acid, which fall to the ground when it rains.
Acid rain can contaminate drinking water, damage vegetation and aquatic life, reduce soil fertility and erode buildings.
- Olivia Rose-Innes, EnviroHealth Editor, Health24, April 2012