To reduce ground-level ozone concentration in a city, which action would be most effective?

To reduce ground-level ozone concentration in a city, which action would be most effective?

• A. Increase NOx emissions
• B. Decrease nitrogen oxides emissions
• C. Increase volatile organic compounds
• D. Increase sulfur dioxide emissions

Answer: (B)

Ground-level ozone forms in the air through sunlight-driven reactions that mix nitrogen oxides (NOx) and volatile organic compounds (VOCs). It isn’t emitted directly; it’s a secondary pollutant created by these precursors. In a city with abundant NOx, lowering NOx reduces the rate at which the ozone-forming chemistry can proceed, so the overall ozone concentration drops. Increasing NOx or VOCs would provide more fuel for those photochemical reactions and raise or sustain higher ozone levels, while sulfur dioxide doesn’t directly drive ozone formation. Therefore, reducing NOx emissions is the most effective single step to lower ground-level ozone in many urban environments.

Ground-level ozone forms in the air through sunlight-driven reactions that mix nitrogen oxides (NOx) and volatile organic compounds (VOCs). It isn’t emitted directly; it’s a secondary pollutant created by these precursors. In a city with abundant NOx, lowering NOx reduces the rate at which the ozone-forming chemistry can proceed, so the overall ozone concentration drops. Increasing NOx or VOCs would provide more fuel for those photochemical reactions and raise or sustain higher ozone levels, while sulfur dioxide doesn’t directly drive ozone formation. Therefore, reducing NOx emissions is the most effective single step to lower ground-level ozone in many urban environments.