A city experiences frequent issues with photochemical smog, especially during sunny summer months. The city's electricity is primarily generated by a nearby coal-fired power plant. Which statement best explains the connection between the power plant and the smog?
- The plant releases large amounts of carbon monoxide, which directly forms a visible brown haze.
- The plant emits sulfur dioxide, which reacts with water vapor to form sulfuric acid aerosols, the main component of smog.
- The plant releases nitrogen oxides (NOx), which react with volatile organic compounds (VOCs) in the presence of sunlight to form ground-level ozone. (correct answer)
- The plant emits particulate matter (soot), which is the primary chemical constituent of photochemical smog.
Explanation: This question requires linking a primary pollutant to a secondary pollutant. Photochemical smog's main component is ground-level ozone (O₃). It is not emitted directly but is formed in the atmosphere through a chemical reaction between primary pollutants—specifically, nitrogen oxides (NOx) from high-temperature combustion (like in coal plants and vehicles) and volatile organic compounds (VOCs)—in the presence of sunlight. A is incorrect; carbon monoxide is a toxic gas but doesn't form the brown haze (which is often NO₂). B describes the formation of industrial smog and acid rain, not photochemical smog. D is incorrect; particulate matter contributes to haze but is not the primary chemical component of photochemical smog.