Distinguish between stratospheric ozone depletion and tropospheric ozone pollution, including their sources and health/environmental impacts.

• A. Stratospheric ozone protects against UV; depletion is caused by CFCs and halons; tropospheric ozone is a pollutant formed from NOx and VOCs under sunlight, harming human health and plant life.
• B. Tropospheric ozone and stratospheric ozone are identical; sources same.
• C. Ozone is not harmful.
• D. Stratospheric ozone forms near the ground.

Answer: (A)

Understanding the difference comes from where the ozone is and what creates it. Stratospheric ozone sits high in the atmosphere and forms a protective shield that blocks most of the sun’s UV-B radiation. When human-made halogenated compounds, especially chlorofluorocarbons and halons, reach the stratosphere, they release chlorine and bromine that catalytically destroy ozone, thinning the ozone layer. The result is more UV reaching the surface, which raises risks of skin cancer, cataracts, and ecological effects from increased UV exposure.

Ground-level ozone, on the other hand, is a secondary pollutant formed in the lower atmosphere by photochemical reactions involving nitrogen oxides and volatile organic compounds in sunlight. NOx and VOCs come from vehicle exhaust, industry, and solvents. This ozone harms human health by irritating the lungs, reducing lung function, triggering or worsening asthma, and irritating the throat. Ecologically, it can damage crops and forests by reducing photosynthesis and growth.

So the correct description highlights the protective role and depletion mechanism of stratospheric ozone, versus the formation and harmful effects of tropospheric ozone near the surface.