Which pollutant is involved in photochemical smog formation with NOx and sunlight?

• A. VOCs
• B. Ground-level ozone
• C. Nitrogen oxides
• D. PM2.5

Answer: (A)

VOCs (volatile organic compounds) are the pollutant that partner with NOx and sunlight to drive photochemical smog. In sunny conditions, VOCs react with the radicals produced during NOx chemistry, forming RO2 and other reactive species that convert NO to NO2 and sustain the production of ozone at ground level. That ozone buildup is the hallmark of photochemical smog. Ground-level ozone is the resulting pollutant from this chemistry, while nitrogen oxides are the precursors, and PM2.5 is a different particulate pollutant that can be present but isn’t the main driver of this photochemical reaction.