Sources of Acid Rain
Acid rain is caused by a chemical reaction that begins when compounds like
sulfur dioxide and nitrogen oxides are released into the air. These substances
can rise very high into the atmosphere, where they mix and react with
water, oxygen, and other chemicals to form more acidic
pollutants, known as acid rain. Sulfur dioxide and nitrogen oxides dissolve
very easily in water and can be carried very far by the wind. As a result,
compounds can travel long distances where they become part of the rain,
and fog that we experience on certain days.
Human activities are the main cause of acid rain. Over the past few decades, humans have released so many different chemicals into the air that they have changed the mix of gases in the atmosphere. Power plants release the majority of sulfur dioxide and much of the nitrogen oxides when they burn fossil fuels, such as coal, to produce electricity. In addition, the exhaust from cars, trucks, and buses releases nitrogen oxides and sulfur dioxide into the air. These pollutants cause acid rain.
Acid Rain is Caused by Reactions in the Environment
Nature depends on balance, and although some rain is naturally acidic,
with a pH level of around 5.0, human activities
have made it worse. Normal precipitation—such
as rain, sleet, or snow—reacts with alkaline
chemicals, or non-acidic materials, that can be found in air, soils,
bedrock, lakes, and streams. These reactions usually neutralize natural
acids. However, if precipitation becomes too acidic, these materials may
not be able to neutralize all of the acids. Over time, these neutralizing
materials can be washed away by acid rain. Damage to crops, trees, lakes,
rivers, and animals can result.