Gases from vehicles and power plants that contribute to smog and acid rain.

• A. Ground-level ozone
• B. Nitrogen oxides
• C. VOCs
• D. PM10

Answer: (B)

Gases from combustion sources that drive both smog formation and acid rain are nitrogen oxides. These pollutants, mainly nitric oxide (NO) and nitrogen dioxide (NO2), are released in high-temperature engines and power plants. They fuel smog by reacting in the sunlight with volatile organic compounds (VOCs) to form ground-level ozone, a major component of photochemical smog. They also contribute to acid rain because they react with water and other chemicals in the atmosphere to form nitric acid and nitrates, which fall as acidic precipitation. Ground-level ozone is a secondary pollutant formed from NOx and VOCs, so while important for smog, NOx are the primary emitted gases that drive both smog and acid rain. VOCs matter for ozone formation but don’t directly cause acid rain, and PM10 refers to particulates, not gases, so they don’t fit as the direct contributors to both smog and acid rain.