Acid rain and its frozen equivalents, acid snow and acid sleet, are part of a larger problem called acid deposition.
Acid rain is one type of atmospheric deposition.
Atmospheric deposition includes any precipitation, airborne particles or gases deposited from the atmosphere to the Earth's surface. Other forms of atmospheric deposition may also be by wet or dry methods. Some air pollutants, such as those in acid rain, can cause environmental problems. Over many decades, the combined input of contaminants to sensitive environments can lead to widespread environmental problems. Acid rain occurs when sulfur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds.