Which pollutant is primarily responsible for acid rain when combined with water vapor?

The primary pollutant responsible for acid rain when combined with water vapor is sulfur dioxide. When sulfur dioxide is released into the atmosphere, it can react with water vapor to form sulfuric acid, which is a key component of acid rain. This process occurs when sulfur dioxide is oxidized in the atmosphere, resulting in acids that fall to the Earth in precipitation.

Acid rain can have detrimental effects on the environment, including damaging aquatic ecosystems, harming vegetation, and eroding buildings and monuments. While other pollutants like nitrogen dioxide can also contribute to acid rain formation through the production of nitric acid, sulfur dioxide is the principal contributor and is often cited as the most significant due to its greater role in acid deposition.

In contrast, carbon monoxide is a different type of pollutant primarily associated with incomplete combustion of fossil fuels and does not contribute to acid rain. Particulate matter is composed of tiny particles and liquid droplets suspended in the air, which can affect air quality and health, but it does not directly contribute to the formation of acid rain. Therefore, the focus on sulfur dioxide highlights its critical role in this environmental issue.