Which set of reactants forms tropospheric ozone?

Which set of reactants forms tropospheric ozone?

• A. NO2 + VOCs + O2 + sunlight
• B. NO + O3 + sunlight
• C. NOx + CO2 + sunlight
• D. NO2 + VOCs + O2 + sunlight

Answer: (D)

Ozone in the lower atmosphere forms through a photochemical process that requires sunlight to drive the reactions. When sunlight breaks apart NO2, it creates NO and a free oxygen atom. That oxygen atom then combines with O2 to make O3, but this would quickly stop unless NO2 is continually regenerated. Hydrocarbons and other volatile organic compounds provide radical reactions that convert NO back to NO2, allowing the cycle to keep producing ozone. The oxygen in ozone comes from the abundant O2 in the air, and the energy input is the sunlight that powers the photolysis steps. So the set that yields tropospheric ozone includes NO2, VOCs, O2, and sunlight. The presence of VOCs is essential to sustain ozone formation; without them, ozone would not accumulate despite the sunlight.

Ozone in the lower atmosphere forms through a photochemical process that requires sunlight to drive the reactions. When sunlight breaks apart NO2, it creates NO and a free oxygen atom. That oxygen atom then combines with O2 to make O3, but this would quickly stop unless NO2 is continually regenerated. Hydrocarbons and other volatile organic compounds provide radical reactions that convert NO back to NO2, allowing the cycle to keep producing ozone. The oxygen in ozone comes from the abundant O2 in the air, and the energy input is the sunlight that powers the photolysis steps. So the set that yields tropospheric ozone includes NO2, VOCs, O2, and sunlight. The presence of VOCs is essential to sustain ozone formation; without them, ozone would not accumulate despite the sunlight.