Acid rain: Rain resulting from the combination of fossil fuel emissions and water in the atmosphere. The environmental effects of acid rain include the acidification of lakes and streams, damage to trees at high altitude, the acceleration of decay in buildings and poorer air quality.

Acid rain also poses serious human health risks by contributing to heart and lung disorders such as asthma and bronchitis. Acid rain can be reduced by the regulation of industrial emissions and the adoption of energy efficiency alternatives and pollution prevention programs. Acid rain is a form of acid deposition.