What atmospheric precursors contribute to acid deposition?

• A. Carbon dioxide is the primary precursor of acid deposition.
• B. Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) form sulfuric and nitric acids in the atmosphere which return as acid rain or deposition.
• C. Water vapor alone drives acid deposition.
• D. Only ammonia contributes to acid deposition.

Answer: (B)

The main idea is that acid deposition comes from gases released when fossil fuels are burned, especially sulfur dioxide and nitrogen oxides. In the atmosphere these gases react with water, oxygen, and other oxidants to form sulfuric acid and nitric acid. When these acids become part of cloud droplets or are present as aerosols, they are deposited as acid rain, snow, or dry deposition, lowering the pH of rain and affecting soils and aquatic systems. Carbon dioxide isn’t a primary precursor of acid deposition, and water vapor alone doesn’t create acidity. Ammonia can contribute to deposition as ammonium compounds, but the key acid-forming precursors are sulfur dioxide and nitrogen oxides that produce sulfuric and nitric acids.