Acid rain, also known as acid deposition or acid precipitation, refers to any form of precipitation that contains acidic components like sulfuric or nitric acid. This includes water in various states such as rain, snow, hail, dew, fog, and dust particles that fall from the sky.

Pure water (distilled water) has no chemicals such as carbon dioxide or other dissolved ions. It is neutral and has a pH reading of 7. pH is a measure of how acidic or basic (alkaline) a liquid is, with 7 being neutral. Liquids with a pH less than 7 are acidic, while those with a pH greater than 7 are basic (or alkaline). A one-unit change in pH represents a tenfold change in the strength of the acid or base being measured.

Rainwater typically has a slightly acidic pH of 5.6 due to the presence of carbon dioxide in the air. When these compounds react with rainwater molecules, they form a weak acid known as carbonic acid.

Acid rain is any form of water that forms in the atmosphere, reacts with acidic components like carbon dioxide, sulfur dioxide, and nitrous oxides, and falls to the land surface.