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Flip to reveal answersWhat are ozone-depleting substances (ODS)?
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All 15 Flashcards — Ozone depletion
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Question
What are ozone-depleting substances (ODS)?
Answer
ODS are chemicals (e.g., CFCs, halons, some HCFCs) that release chlorine or bromine in the stratosphere and destroy ozone.
💡 Hint
CFCs and halons.
Question
State the main cause of stratospheric ozone depletion.
Answer
Ozone depletion is mainly caused by ODS (especially CFCs and halons) releasing chlorine/bromine that catalytically destroys ozone.
💡 Hint
ODS → reactive halogens.
Question
Define the ozone hole.
Answer
The ozone hole is a region of severely depleted ozone in the stratosphere that forms seasonally (mainly over Antarctica) during spring.
💡 Hint
Seasonal depletion, not a literal hole.
Question
Why does the ozone hole form mainly over Antarctica?
Answer
A strong polar vortex isolates air, extreme cold allows polar stratospheric clouds (PSCs) to form, and returning spring sunlight triggers rapid ozone destruction.
💡 Hint
Vortex + PSCs + sunlight.
Question
Give two common uses of CFCs (historically).
Answer
CFCs were used in refrigerators/air conditioners, aerosol sprays, and foam/blowing agents.
💡 Hint
Cooling + aerosols/foam.
Question
What does “catalytic” mean in ozone destruction?
Answer
Catalytic means the chlorine/bromine is regenerated and not used up, so it can destroy many ozone molecules repeatedly.
💡 Hint
Reused, not consumed.
Question
What is a polar vortex in the context of the ozone hole?
Answer
A circular wind pattern that isolates Antarctic stratospheric air during winter, helping conditions build up for ozone depletion.
💡 Hint
Isolation of air mass.
Question
Why can small amounts of CFCs cause large ozone loss?
Answer
Because chlorine from CFCs acts catalytically: it destroys ozone and is regenerated, so one chlorine atom can destroy many ozone molecules.
💡 Hint
Catalyst = reused.
Question
Why is ozone recovery slow even after phasing out CFCs?
Answer
CFCs persist in the atmosphere for decades, so existing CFCs continue reaching the stratosphere and releasing chlorine long after production stops.
💡 Hint
Long residence time.
Question
State the key steps of the catalytic ozone destruction cycle (simplified).
Answer
Cl + O3 → ClO + O2, then ClO + O → Cl + O2. Chlorine is regenerated and can repeat the cycle.
💡 Hint
Cl is recycled.
Question
Describe the typical trend of the ozone hole since the late 20th century.
Answer
It increased in size/severity through the late 20th century, then stabilised and has shown signs of slow recovery since around the early 2000s.
💡 Hint
Rise → stabilise → slow recovery.
Question
What role do polar stratospheric clouds (PSCs) play in ozone depletion?
Answer
PSCs provide surfaces for chemical reactions that convert chlorine into reactive forms, priming the stratosphere for rapid ozone destruction when sunlight returns.
💡 Hint
PSCs activate chlorine.
Question
When does the Antarctic ozone hole usually become largest?
Answer
It typically develops in September–October (Southern Hemisphere spring) and then shrinks toward summer.
💡 Hint
Spring peak.
Question
Why do ODS take time to affect the ozone layer?
Answer
They are stable and can persist long enough to rise to the stratosphere, where UV radiation breaks them down to release reactive chlorine/bromine.
💡 Hint
Stable → reach stratosphere.
Question
What is one common exam command-word skill in ozone depletion questions?
Answer
Clearly explain the catalytic mechanism (or the Antarctic conditions) using a stepwise chain and correct key terms (ODS, chlorine, PSCs, polar vortex, UV).
💡 Hint
Use key terms + chain.
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Full study notes for Ozone depletion
Topic 6.4 hub
Stratospheric ozone
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