Acid rain is basically when harmful chemicals fall onto the earth in the form of rain.

Acid rain occurs when harmful chemicals ( such as Sulphur dioxide and Nitrogen oxides) are emitted in the atmosphere from natural and human emissions.The harmful gases are absorbed by clouds, and the clouds carry the chemicals for a while in the form of liquid.Eventually, the clouds will drop the chemicals in one of several forms (rain, sleet, snow, etc.).

The chemicals drop on the earth, and cause harmful effects to the environment, wildlife, and even humans.