Why is ozone called a pollutant in the lower troposphere and a protector in the stratosphere?

Correct answer: Its effect changes with location

The correct answer is A: ozone’s effect changes according to its location in the atmosphere. In the lower troposphere, ozone is usually a secondary pollutant. It forms through sunlight-driven chemical reactions involving nitrogen oxides and volatile organic compounds. At higher concentrations near the ground, it can irritate the respiratory system and damage plants and materials. In the stratosphere, ozone has a beneficial protective role because it absorbs much of the Sun’s harmful ultraviolet radiation before that radiation reaches Earth’s surface. The ozone molecule is still O₃ in both regions; its different effect results from its altitude, surrounding chemistry and interaction with living organisms. B is wrong because ozone is not simply oxygen everywhere; oxygen gas is O₂, whereas ozone is O₃. C is wrong because ozone is a gas, not dust. D is wrong because ozone is not a form of nitrogen. Memory cue: “bad near the ground, protective high above.”