Ozone formation in upper atmosphere
UV splits O₂; O + O₂ → O₃ (ozone).
Step 1 — Study the figure
Cover the label key on the image, name each numbered part, then check the explanations below.
Step 2 — Diagram details for students
What this diagram shows
Ozone in the upper atmosphere forms when UV light splits oxygen molecules and free oxygen atoms join O₂ to make O₃. This ozone layer absorbs harmful UV radiation. CFCs deplete ozone, which is why international controls were needed.
Numbered parts — mark & remember
Match each number on the figure with the meaning below. Say the function aloud once.
1 UV radiation
Ultraviolet radiation from the sun provides energy to break O₂ molecules. High-energy UV is harmful to living tissues. Stratospheric ozone helps shield Earth’s surface from much of this UV.
2 O₂ split
UV splits an oxygen molecule into two oxygen atoms. This is the first step of ozone formation. Without this splitting, the next combination step cannot occur.
3 O + O₂ → O₃
A free oxygen atom combines with an O₂ molecule to form ozone O₃. This reaction builds and maintains the ozone shield. Write the stepwise formation clearly in exams.
4 Ozone shield / depletion
Ozone absorbs UV and protects life. CFC compounds release chlorine that destroys ozone molecules. UNEP agreements helped freeze CFC production to reduce further damage.
How to read this figure
- Two steps: split O₂, then form O₃.
- Good ozone is high up; do not confuse with local air pollution ozone casually.
- Link CFCs to depletion for reason questions.
Redraw for board marks
- Draw sun UV arrow hitting O₂.
- Show O atoms then O₃ formation.
- Add a shield note and CFC depletion note.
Board answer tip: Write ozone formation in two steps, state its use, and explain CFC depletion in three lines.
Exam tips — don’t lose marks
- Learn the formation equations/steps in words.
- CFC–ozone depletion is a must-mention pair.
- State UV harm to living organisms briefly.