Acid rain is rain or any other form of precipitation that is unusually
acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most
water, including drinking water, has a neutral pH that exists between 6.5 and
8.5, but acid rain has a pH level lower than this and ranges from 4–5 on
average. The more acidic the acid rain is, the lower its pH is. Acid rain can
have harmful effects on plants, aquatic animals, and infrastructure. Acid rain
is caused by emissions of sulfur dioxide and nitrogen oxide, which react with
the water molecules in the atmosphere to produce acids.
Acid rain has been shown to have adverse impacts on forests, freshwaters,
soils, microbes, insects and aquatic life-forms.