Which acids formed from sulfur dioxide and nitrogen oxides are primarily responsible for atmospheric deposition leading to acid rain?

• A. Sulfuric and nitric acids formed from sulfur dioxide (SO2) and nitrogen oxides (NOx)
• B. Hydrochloric acid and acetic acid formed from chlorine and VOCs
• C. Sulfurous acid and nitrous acid formed from sulfur dioxide and nitrogen monoxide
• D. Carbonic acid and nitric acid formed from carbon dioxide and NOx

Answer: (A)

Acid rain is caused mainly by sulfuric and nitric acids forming from sulfur dioxide and nitrogen oxides in the atmosphere. Sulfur dioxide dissolves in cloud droplets and is oxidized to sulfate, which combines with water to make sulfuric acid (H2SO4) that falls with precipitation. Nitrogen oxides, especially NO2, react with hydroxyl radicals and water to form nitric acid (HNO3), which also dissolves in rain. These two acids are highly effective at lowering rainwater pH and are the primary drivers of acid deposition. The other acids listed aren’t produced in the same dominant way from SO2 and NOx—for example, carbonic acid comes from CO2, and acids like hydrochloric or acetic acids arise from different sources—so they don’t contribute to acid rain as the main species.