acid rain 
noun [mass noun]
Rainfall made so acidic by atmospheric pollution that it causes environmental harm, chiefly to forests and lakes. The main cause is the industrial burning of coal and other fossil fuels, the waste gases from which contain sulphur and nitrogen oxides which combine with atmospheric water to form acids.Power generated from fossil fuels causes smog, mercury pollution, acid rain and global warming....
- Coal is the most polluting fuel in our energy mix contributing, among other things, to smog, acid rain and global warming.
- Trees also clear the air of sulfur dioxide and nitrogen oxide, two major components of acid rain and ozone pollution.