Here's how it works:

* Sulfur dioxide (SO2) is a colorless gas released primarily from burning fossil fuels.

* Rainwater is naturally slightly acidic due to dissolved carbon dioxide, but it becomes much more acidic when it absorbs SO2.

* The SO2 reacts with water to form sulfurous acid (H2SO3), which further oxidizes to sulfuric acid (H2SO4).

* Sulfuric acid is a strong acid that significantly lowers the pH of rainwater, creating acid rain.

Acid rain has various harmful effects, including:

* Damaging forests and crops by damaging leaves and reducing nutrient absorption.

* Eroding buildings and monuments, especially those made of limestone and marble.

* Acidifying lakes and streams, harming aquatic life.

* Contributing to respiratory problems in humans.