# Acid Rain

Most of the Earth is covered in water. As such, most chemical reactions take place in aqueous solutions. Many of these reactions impact our environment and the lifeforms that inhabit our planet. Some of these reactions are due to the human impact on the planet. Efforts are being made to minimize the negative effects human activity has had on the planet.

## Acid Rain

Any precipitation (rain or snow) that has a pH lower than 5.7 is considered acid rain. It is caused by emissions of sulfur dioxide and nitrogen oxides; these emissions react with the water in our atmosphere to produce acids. Sulfur dioxide can be produced by volcanic eruptions and nitrogen dioxides by lightning strikes. Most of the harmful chemical are released by human activities. These chemicals travel up into the atmosphere, mix with rain clouds, and fall in the form of acid rain. The acid rain can cause corrosion of steel structures such as bridges, stone statues, and the peeling of paint. Much of these chemicals originate from electricity generation, factories, and motor vehicles.

• Sulfur dioxide is oxided by reaction with the hydroxyl radical according to the following reactions:

$SO_2 + OH \rightarrow HOSO_2$

$HOSO_2 + O_2 \rightarrow HO_2 + SO_3$

• In the presence of water, sulfur trioxide becomes sulfuric acid:

$SO_3 + H_2O \rightarrow \underbrace{H_2SO_4}_{\text{sulfuric acid}}$

$NO_2 + OH \rightarrow \underbrace{HNO_3}_{\text{nitric acid}}$

• In a cloud, sulfur dioxide can by hydrolyzed:

$SO_{2 (g)} + H_2O \rightleftharpoons SO_2 \cdot H_2O$

$SO_2 \cdot H_2O \rightleftharpoons H^+ + HSO_3^−$

$HSO_3^− \rightleftharpoons H^+ + SO_3^{2−}$

From ChemPRIME:11.8: Strong Acids and Bases