Volatile organic compounds that react with NOx to form photochemical smog.

• A. PM2.5
• B. Ground-level ozone
• C. Particulate matter
• D. VOCs

Answer: (D)

Volatile organic compounds drive photochemical smog formation by reacting with NOx in the presence of sunlight. These VOCs come from solvents, fuels, paints, and numerous consumer and industrial sources, and when sunlight hits them, they participate in radical reactions that transform NOx into ozone and other oxidants. Ground-level ozone is a major product of this chemistry, but it’s formed from VOCs and NOx rather than being the VOC itself. Particulate matter (PM2.5) consists of tiny particles and is a separate component of smog, not the reactive VOCs. So, the class that reacts with NOx to form photochemical smog is the volatile organic compounds.