We eat food, drink water, and breathe air that has come in contact with acid deposition.

　　Canadian and U.S. studies indicate that there is a link between this pollution and respirator problems in sensitive populations such as children and asthmatics.

　　Acid deposition can increase the levels of toxic metals such as aluminum, copper, and mercury in untreated drinking water supplies.

　　What causes acid rain?

　　Acid rain is rain, snow or fog that is polluted by acid in the atmosphere and damages the environment. Two common air pollutants acidify rain: sulphur dioxide (SO₂) and nitrogen oxide (NO_X). When these substances are releasedsintosthe atmosphere, they can be carried over long distances by prevailing winds and return to earth as acidic rain, snow, fog or dust. When the environment cannot neutralize the acid being deposited, damage occurs.

　　What does acid mean?