On a dark and cloudy day, what is the predicted pattern for nitrogen dioxide and ground-level ozone readings?

On a dark and cloudy day, what is the predicted pattern for nitrogen dioxide and ground-level ozone readings?

• A. There will be an increase in the level of nitrogen dioxide and a decrease in the level of ground-level ozone.
• B. There will be a decrease in nitrogen dioxide and an increase in ground-level ozone.
• C. Both NO2 and O3 increase.
• D. Both NO2 and O3 decrease.

Answer: (A)

On a dark, cloudy day, the amount of sunlight is minimal, which slows the photochemical reactions that produce ground-level ozone. Ozone at the surface forms when NO2 is broken apart by photons to produce atomic oxygen, which then combines with O2 to make O3. Without enough light, this step happens less, so ozone formation drops. At the same time, nitrogen dioxide can accumulate because its destruction by photolysis is reduced and ongoing emissions keep adding NO2 to the air. Additionally, any ozone that is present can be consumed by reactions with NO to form more NO2, reinforcing the drop in ozone. So nitrogen dioxide tends to increase while ground-level ozone decreases.

On a dark, cloudy day, the amount of sunlight is minimal, which slows the photochemical reactions that produce ground-level ozone. Ozone at the surface forms when NO2 is broken apart by photons to produce atomic oxygen, which then combines with O2 to make O3. Without enough light, this step happens less, so ozone formation drops. At the same time, nitrogen dioxide can accumulate because its destruction by photolysis is reduced and ongoing emissions keep adding NO2 to the air. Additionally, any ozone that is present can be consumed by reactions with NO to form more NO2, reinforcing the drop in ozone. So nitrogen dioxide tends to increase while ground-level ozone decreases.