Acid rain is the common name for acidic deposits that fall to Earth from the atmosphere. The term was coined in 1872 by English chemist Robert Angus Smith to describe the acidic precipitation in Manchester, England.
Today, scientists study both wet and dry acidic deposits.
Although there are natural sources of acid in the atmosphere, acid rain is primarily caused by emissions of SO2 and nitrous oxide (N2O) from electric utilities burning fossil fuels, especially coal.
These chemicals are converted to sulphuric acid and nitric acid in the atmosphere and can be carried by the winds for many miles from where the original emissions took place.
Wet deposition occurs when the acid falls in rain, snow, or ice.
Dry deposition is caused by very tiny particles (or particulates) in combustion emissions.
They may stay dry as they fall or pollute cloud water and precipitation.
Moist deposition occurs when the acid is trapped in cloud or fog droplets.
This is most common at high altitudes and in coastal areas.
Whatever its form, acid rain can create dangerously high levels of acidic impurities in water, soil and plants.
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