IB Environmental systems and societies Topic 6.4D Stratospheric Ozone Depletion and Odss Revision Notes (HL)

IB Environmental systems and societies Topic 6.4D Stratospheric Ozone Depletion and Odss Revision Notes (HL) | RevisionDojo

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The Catalytic Mechanism: How One Chlorine Atom Destroys Thousands of Ozone Molecules

ODSs such as CFCs, HCFCs, carbon tetrachloride and methyl chloroform are stable in the troposphere but break down under UV radiation in the stratosphere.
This UV breakdown releases chlorine and bromine radicals.
These radicals catalytically destroy ozone, and are regenerated rather than used up.
One chlorine radical can destroy up to 100,000 ozone molecules before it is deactivated.
CFCs are especially damaging because they have long atmospheric lifetimes (over 100 years) and spread globally.

Note

CFCs break down and release a chlorine radical (Cl).
Cl reacts with ozone (O₃), forming chlorine monoxide (ClO) and O₂.
ClO reacts with a free oxygen atom (O), releasing Cl to repeat the cycle.
Net effect: O₃ and O are converted into two O₂ molecules.

Major Ozone-Depleting Substances and Their Potency

ODS	Sources	Harmful Element Released	Ozone Depletion Potential (ODP)
CFC-11 (Trichlorofluoromethane)	Refrigerators, air conditioners, foam insulation	Chlorine (Cl)	1.0
CFC-12 (Dichlorodifluoromethane)	Aerosols, propellants, solvents	Chlorine (Cl)	1.0
Halon-1301 (Bromotrifluoromethane)	Fire extinguishers	Bromine (Br)	10.0
Carbon Tetrachloride (CCl₄)	Industrial solvent, dry cleaning	Chlorine (Cl)	1.1
Methyl Bromide (CH₃Br)	Pesticides, fumigation	Bromine (Br)	0.6

Note

Bromine compounds such as halons and methyl bromide are even more destructive than chlorine.
One bromine atom can destroy up to 100 times more ozone than one chlorine atom.

Why the Ozone Hole Forms Over Antarctica in Spring

Definition

Polar Stratospheric Clouds

Ice-based clouds that form only at extremely low stratospheric temperatures and enable reactions that convert stored chlorine into ozone-destroying radicals.

The most severe depletion is over Antarctica in spring (September to November).
Extreme winter cold (as low as −90 °C) forms polar stratospheric clouds (PSCs) of ice and nitric acid.
PSC surfaces convert inactive chlorine compounds into highly reactive forms.

Analogy

PSCs act like charging stations for chlorine radicals.
They prime inactive chlorine to become highly destructive once sunlight returns.

The Polar Vortex and Why Antarctica Beats the Arctic

A polar vortex forms over Antarctica in winter, isolating the air and trapping ODSs and reactive halogens.
This isolation prevents dilution with lower-latitude air, concentrating ozone-destroying chemicals.

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The Catalytic Mechanism: How One Chlorine Atom Destroys Thousands of Ozone Molecules

ODSs such as CFCs, HCFCs, carbon tetrachloride and methyl chloroform are stable in the troposphere but break down under UV radiation in the stratosphere.
This UV breakdown releases chlorine and bromine radicals.
These radicals catalytically destroy ozone, and are regenerated rather than used up.
One chlorine radical can destroy up to 100,000 ozone molecules before it is deactivated.
CFCs are especially damaging because they have long atmospheric lifetimes (over 100 years) and spread globally.

Note

CFCs break down and release a chlorine radical (Cl).
Cl reacts with ozone (O₃), forming chlorine monoxide (ClO) and O₂.
ClO reacts with a free oxygen atom (O), releasing Cl to repeat the cycle.
Net effect: O₃ and O are converted into two O₂ molecules.

Major Ozone-Depleting Substances and Their Potency

ODS	Sources	Harmful Element Released	Ozone Depletion Potential (ODP)
CFC-11 (Trichlorofluoromethane)	Refrigerators, air conditioners, foam insulation	Chlorine (Cl)	1.0
CFC-12 (Dichlorodifluoromethane)	Aerosols, propellants, solvents	Chlorine (Cl)	1.0
Halon-1301 (Bromotrifluoromethane)	Fire extinguishers	Bromine (Br)	10.0
Carbon Tetrachloride (CCl₄)	Industrial solvent, dry cleaning	Chlorine (Cl)	1.1
Methyl Bromide (CH₃Br)	Pesticides, fumigation	Bromine (Br)	0.6

Note

Bromine compounds such as halons and methyl bromide are even more destructive than chlorine.
One bromine atom can destroy up to 100 times more ozone than one chlorine atom.

Why the Ozone Hole Forms Over Antarctica in Spring

Definition

Polar Stratospheric Clouds

Ice-based clouds that form only at extremely low stratospheric temperatures and enable reactions that convert stored chlorine into ozone-destroying radicals.

The most severe depletion is over Antarctica in spring (September to November).
Extreme winter cold (as low as −90 °C) forms polar stratospheric clouds (PSCs) of ice and nitric acid.
PSC surfaces convert inactive chlorine compounds into highly reactive forms.

Analogy

PSCs act like charging stations for chlorine radicals.
They prime inactive chlorine to become highly destructive once sunlight returns.

The Polar Vortex and Why Antarctica Beats the Arctic

A polar vortex forms over Antarctica in winter, isolating the air and trapping ODSs and reactive halogens.
This isolation prevents dilution with lower-latitude air, concentrating ozone-destroying chemicals.

Definition

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Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

IB Environmental systems and societies 6.4D Stratospheric Ozone Depletion and Odss Notes

Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

The Catalytic Mechanism: How One Chlorine Atom Destroys Thousands of Ozone Molecules

Major Ozone-Depleting Substances and Their Potency

Why the Ozone Hole Forms Over Antarctica in Spring

The Polar Vortex and Why Antarctica Beats the Arctic

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

The Catalytic Mechanism: How One Chlorine Atom Destroys Thousands of Ozone Molecules

Major Ozone-Depleting Substances and Their Potency

Why the Ozone Hole Forms Over Antarctica in Spring

The Polar Vortex and Why Antarctica Beats the Arctic

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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