Which statement best distinguishes tropospheric ozone from stratospheric ozone?

• A. Tropospheric ozone forms near ground from pollutants and can harm health; stratospheric ozone forms naturally in the upper atmosphere and protects against UV radiation.
• B. Tropospheric ozone forms in the upper atmosphere and protects against UV radiation.
• C. Both form near the ground; only difference is color.
• D. Tropospheric ozone is beneficial in all cases; stratospheric ozone causes smog.

Answer: (A)

The important distinction is where the ozone sits and what it does. Near the ground, in the troposphere, ozone is formed by reactions involving pollutants such as NOx and volatile organic compounds under sunlight. This tropospheric ozone is a pollutant that can harm human health, reduce lung function, and contribute to smog. Up higher, in the stratosphere, ozone is produced naturally when UV light splits oxygen molecules, creating an ozone layer that absorbs most of the sun’s harmful ultraviolet radiation and protects living things from UV damage.

So the statement that tropospheric ozone forms near the ground from pollutants and can harm health, while stratospheric ozone forms naturally in the upper atmosphere and protects against UV radiation, best captures the difference.

The other options mix up where ozone forms, its role, or both, which is why they don’t fit.