Which phenomenon is commonly referred to as acid rain?

• A. Smog
• B. Acid Deposition
• C. Air Pollution
• D. Ozone Depletion

Answer: (B)

Acid rain is actually the rainfall form of a broader process called acid deposition. When fossil fuel combustion releases sulfur dioxide and nitrogen oxides, these gases react in the atmosphere to form sulfuric and nitric acids. These acids then dissolve into cloud moisture and fall as precipitation with a low pH, which we commonly call acid rain. But acid deposition also includes dry deposition of acidic particles and gases that settle onto surfaces. So the best term for this whole phenomenon is acid deposition, with acid rain being the wet deposition component. Smog and general air pollution describe broader air quality issues, while ozone depletion refers to stratospheric ozone loss, not this acid-forming deposition.