The two main chemical reactions that occur when sulfur dioxide (SO₂) and nitrogen oxides (NOx) react with water in rain clouds are:

1. Formation of Sulfuric Acid (H₂SO₄):

* SO₂ + H₂O → H₂SO₃ (Sulfurous acid)

* H₂SO₃ + ½ O₂ → H₂SO₄ (Sulfuric acid)

This reaction involves sulfur dioxide dissolving in water to form sulfurous acid (H₂SO₃). Sulfurous acid is then oxidized by atmospheric oxygen to form sulfuric acid (H₂SO₄). Sulfuric acid is a strong acid that contributes significantly to acid rain.

2. Formation of Nitric Acid (HNO₃):

* NO₂ + H₂O → HNO₂ (Nitrous acid)

* 2 HNO₂ + ½ O₂ → 2 HNO₃ (Nitric acid)

Nitrogen dioxide (NO₂) dissolves in water to form nitrous acid (HNO₂). Nitrous acid can then be further oxidized by atmospheric oxygen to form nitric acid (HNO₃), another strong acid contributing to acid rain.

These reactions are a simplified representation of complex processes occurring in the atmosphere. The presence of other atmospheric components and varying conditions can influence the rates and pathways of these reactions. However, they provide a basic understanding of how sulfur dioxide and nitrogen oxides lead to the formation of acid rain.