What term describes the phenomenon where air pollutants react with water to form an acid that precipitates from the sky?

• A. Smog
• B. Air Pollution
• C. Acid Rain
• D. Acid Deposition

Answer: (D)

Acid deposition describes acids formed when air pollutants such as sulfur dioxide and nitrogen oxides react with water in the atmosphere and are deposited onto the surface as precipitation or through dry deposition. This term encompasses the whole process—acidic substances forming in the air and then falling to Earth—whether as rain, snow, or other forms. Smog is a hazy, pollutant-laden condition that affects air quality but isn’t defined by acids precipitating from the sky. Air pollution is the broad presence of contaminants in the air, not the specific deposition of acids. So the phenomenon described is acid deposition.