Chlorine from CFCs catalytically destroys stratospheric ozone.
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The ozone layer in the stratosphere absorbs most harmful UV-B radiation, and it is depleted by catalytic reactions involving chlorine and bromine atoms. Chlorofluorocarbons released at ground level are stable enough to reach the stratosphere, where UV light releases chlorine atoms. A chlorine atom reacts with ozone to form ClO and O2, and ClO reacts with an oxygen atom to regenerate Cl, so one chlorine atom can destroy many thousands of ozone molecules. The Montreal Protocol of 1987 phased out CFCs and similar substances, and the ozone layer is now recovering. Antarctic ozone holes form each spring under polar stratospheric clouds.
Key ideas: Ozone (O3) in the stratosphere (15 to 35 km) absorbs UV-B and UV-C. Cl atoms from CFCs catalyze destruction: Cl plus O3 gives ClO plus O2, then ClO plus O gives Cl plus O2, each Cl destroying about 100000 ozone molecules. Antarctic hole forms in spring via polar stratospheric clouds. The Montreal Protocol (1987) phased out CFCs, and recovery is expected about 2066.
Common mistakes and connections: Mistake: confusing the ozone hole with global warming, or thinking ozone is a pollutant everywhere; it protects aloft but harms in the troposphere. Ozone is measured in Dobson units, hole below 220 DU. Links to radical chain reactions and catalysis.
The ozone layer absorbs most UV-C and UV-B, which is why chlorine catalysed ozone loss increases harmful UV reaching the surface. The interactive lesson shows this as a live animation or chart.
The steps Cl + O3 gives ClO + O2 and ClO + O gives Cl + O2 form a catalytic cycle that destroys ozone.
Chlorine from CFCs catalytically destroys stratospheric ozone.
Ozone Layer Depletion is a intermediate topic in Biochemistry, Environment & Industry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Biochemistry, Environment & Industry first: Global Warming, Greenhouse Gases, Carbon Cycle.
The next topics in Biochemistry, Environment & Industry are CFCs and Smog.
Yes. The interactive lesson includes a self-check question on Ozone Layer Depletion, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.
Ozone Layer Depletion is topic 74 of 127 in Biochemistry, Environment & Industry.
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