Which emissions contribute to acid deposition after atmospheric reactions?

• A. SO2 and NOx
• B. CO2 and CH4
• C. O3 and VOCs
• D. NH3 and Cl-

Answer: (A)

The main idea is that acid deposition comes from gases in the atmosphere that are transformed into acids before they’re deposited as rain, snow, or dust. The strongest contributors are sulfur dioxide and nitrogen oxides. When SO2 is released, it reacts in the air with oxygen and hydroxyl radicals to form sulfuric acid (H2SO4). Nitrogen oxides, produced by combustion, oxidize to form nitric acid (HNO3). These acids mix with cloud water and precipitate as acid rain or settle as dry acidic particles, lowering pH in soils and water bodies.

CO2 and CH4 are greenhouse gases that affect climate, not direct acid formation in rain. O3 and VOCs drive smog chemistry, not the acid deposition process. Ammonia (NH3) can participate in forming ammonium salts, which can influence aerosol composition, but it tends to neutralize acidity rather than create it, and chloride isn’t a primary acid-deposition precursor.

So, the emissions that directly lead to acid deposition through atmospheric acid formation are sulfur dioxide and nitrogen oxides.