Where is the majority of Earth's ozone located?

• A. Troposphere
• B. Mesosphere
• C. Ionosphere
• D. Stratosphere

Answer: (A)

The main idea here is where ozone really concentrates and why that location matters. Most of Earth’s ozone sits in the stratosphere, forming the ozone layer about 10 to 50 kilometers up, with the strongest amounts around 20–30 kilometers. Ozone forms when UV light from the Sun breaks apart oxygen molecules, and in the stratosphere this ozone builds up because the conditions are right for it to accumulate and persist. The troposphere near the surface does have ozone, largely from pollution and some natural sources, but its total mass is much smaller than in the stratosphere. The ionosphere is much higher and not where the bulk of ozone is found. This stratospheric ozone is vital because it absorbs most of the Sun’s harmful ultraviolet radiation, protecting life on Earth.