One of the main acids in acid rain forms when water combines with sulfur dioxide (SO2).

Here's how it happens:

1. Sulfur dioxide is released into the atmosphere primarily from burning fossil fuels.

2. In the atmosphere, sulfur dioxide reacts with water, oxygen, and other substances to form sulfuric acid (H2SO4).

3. This sulfuric acid then dissolves in rainwater, making it acidic.

Important Note: While sulfuric acid is the primary component, nitric acid (HNO3) is also a significant contributor to acid rain. Nitric acid forms similarly, but starts with nitrogen oxides (NOx) released from combustion.