Ozone depletion by CFCs template

Free-radical destruction of stratospheric ozone for A-level and NCERT: how ozone forms and absorbs UV (Chapman cycle), initiation by UV homolysis of a CFC (CF₂Cl₂), the propagation steps Cl· + O₃ → ClO· + O₂ and ClO· + O₃ → Cl· + 2O₂ drawn as a catalytic cycle, the net 2O₃ → 3O₂, and the similar NO· cycle.

What the template shows

• UV splits a C–Cl bond; the chlorine radical then destroys ozone in a chain: 2O₃ → 3O₂
• Ozone layer: made and broken by UV
• Propagation: the chlorine cycle
• UV, λ < 320 nm: this absorption shields the Earth
• Initiation: UV breaks a CFC
• UV in the stratosphere: the weaker C–Cl bond breaks (homolysis), not C–F
• Nitrogen monoxide does the same
• net: NO· (from aircraft and lightning) is a catalyst too
• Cl· is regenerated: it is a catalyst
• CFCs are unreactive and non-toxic, so they survive long enough to drift into the stratosphere, where UV breaks the C–Cl bond (weaker than C–F) to give chlorine radicals.
• Cl· is used in the first propagation step and regenerated in the second, so it acts as a catalyst: one chlorine atom can destroy many thousands of ozone molecules before it is trapped.
• Chain termination: radicals combine or form reservoir molecules (HCl, ClONO₂), which polar stratospheric clouds turn back into Cl₂ each spring, giving the Antarctic ozone hole.
• The Montreal Protocol (1987) phased out CFCs. Replacements such as HFCs (e.g. CH₂FCF₃) have no C–Cl bond, so they do not deplete ozone (but are greenhouse gases).
• Every part of this figure is editable · sources on the template card

Drawn with 148 shapes – every one editable in MolDraw.

Sources

• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018, ch. 16 Textbook
• NCERT, Chemistry Part II, Class XI (pre-2023 edition), ch. 14 Environmental Chemistry Textbook