Volatile organic compounds generated in the atmosphere contribute to the formation of which pollutant?

• A. Ozone
• B. Sulfuric acid
• C. Particulate matter
• D. Water vapor

Answer: (A)

Volatile organic compounds act as precursors in photochemical smog by driving reactions that form ozone in the lower atmosphere. In sunlight, VOCs react with oxidants like hydroxyl radicals to produce RO2 (peroxy) radicals. These RO2 species transfer their oxidizing power to nitric oxide, converting it to nitrogen dioxide. When NO2 is exposed to sunlight, it photolyzes to give an oxygen atom, which quickly combines with O2 to form ozone. This sequence requires sunlight and the presence of NOx, making ground-level ozone a common pollutant linked to urban air quality problems. Sulfuric acid forms mainly from sulfur dioxide oxidation, not directly from VOCs; water vapor is not produced specifically by VOC oxidation, and while VOCs can contribute to particulate matter through secondary organic aerosol formation, the pollutant most directly formed from this VOC-driven chemistry under sunlight is ozone.