Sulfur dioxide (SO2) reacts with water droplets in the air to form sulfurous acid (H2SO3). This process, known as aqueous-phase oxidation, is one of the main pathways for the formation of acid rain.

Chemical Reaction:

SO2 + H2O → H2SO3

Acid Rain Formation:

In the presence of sunlight and oxygen, sulfurous acid further oxidizes to form sulfuric acid (H2SO4), which is the primary component of acid rain. The overall chemical reactions for the formation of sulfuric acid from sulfur dioxide are:

SO2 + H2O + 1/2O2 → H2SO3

H2SO3 + 1/2O2 → H2SO4

Acid rain can have several adverse effects on the environment, including acidification of lakes and streams, damage to forests, corrosion of buildings and infrastructure, and harm to human health.