What causes acid rain, and what are its environmental impacts?

• A. Methane forms acids in rain.
• B. Carbon dioxide alone causes acid rain.
• C. Ozone destruction causes acid rain.
• D. Sulfur dioxide and nitrogen oxides form acids in the atmosphere; lowers pH of water and soils, damages ecosystems and buildings.

Answer: (D)

Acid rain is driven by sulfur dioxide and nitrogen oxides released when fossil fuels are burned. In the atmosphere these gases react with oxygen and water to form sulfuric acid and nitric acid. When these acids dissolve in rain, the pH drops, so rain becomes acidic and can also deposit as dry acidic particles. This acidity travels with weather patterns and can affect areas far from the original sources.

The environmental impacts are broad. In water, lower pH damages aquatic life, reducing biodiversity and upsetting ecosystems. In soils, acidity can cause important nutrients to leach away and increase the solubility of toxic metals like aluminum, harming plant roots and microbial activity. Forests can suffer as trees experience stress and slower growth. Buildings and monuments made of limestone or marble, as well as some metals, can corrode more easily due to the acidic moisture.

The other options don’t fit because methane and carbon dioxide aren’t the main drivers of acid rain in the atmosphere, and ozone destruction isn’t the mechanism that creates the acids responsible for acid rain. What actually forms the acids in rain are sulfur dioxide and nitrogen oxides.