Which layer contains the ozone layer?

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

Answer: (D)

The layer that contains the ozone layer is the stratosphere. This part of the atmosphere sits above the troposphere, roughly from about 10 to 50 kilometers up. Ozone forms when ultraviolet radiation splits oxygen molecules, allowing individual atoms to join with O2 to make O3. The ozone molecules strongly absorb UV light, which heats the surrounding air and creates a temperature increase with height in this region, helping to form a relatively stable, layered region. That combination of chemistry and the temperature profile makes the stratosphere the main home of most atmospheric ozone. Farther up, the mesosphere and thermosphere have far less ozone and different conditions, while ozone is also present near the surface in the troposphere as a pollutant, but not in the concentration that defines the ozone layer.