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Questions and Answers
What is the term used to describe the very low values of total ozone that encircle the Antarctic continent?
What is the term used to describe the very low values of total ozone that encircle the Antarctic continent?
ozone hole
In which month do low total ozone values typically appear in the Antarctic?
In which month do low total ozone values typically appear in the Antarctic?
October
What instrument was used for the first total ozone measurements in Antarctica?
What instrument was used for the first total ozone measurements in Antarctica?
Dobson spectrophotometers
What were the average total ozone values observed in the Antarctic spring in the 1950s?
What were the average total ozone values observed in the Antarctic spring in the 1950s?
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Total ozone values in Antarctica are higher than those in the Arctic during spring.
Total ozone values in Antarctica are higher than those in the Arctic during spring.
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What atmospheric phenomenon contributes to the lower total ozone values in Antarctica?
What atmospheric phenomenon contributes to the lower total ozone values in Antarctica?
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Why has an 'ozone hole' appeared over Antarctica?
Why has an 'ozone hole' appeared over Antarctica?
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Ozone-depleting substances are only present in the Antarctic stratosphere.
Ozone-depleting substances are only present in the Antarctic stratosphere.
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What chemical conditions in Antarctica contribute to the formation of the ozone hole?
What chemical conditions in Antarctica contribute to the formation of the ozone hole?
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What temperature must be reached for polar stratospheric clouds (PSCs) to form?
What temperature must be reached for polar stratospheric clouds (PSCs) to form?
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What is the primary gas formed from reactions on PSC particles that destroys ozone?
What is the primary gas formed from reactions on PSC particles that destroys ozone?
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The process where nitric acid and water are removed from the stratosphere due to falling PSC particles is called __________.
The process where nitric acid and water are removed from the stratosphere due to falling PSC particles is called __________.
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How long do polar stratospheric clouds typically last over Antarctica compared to the Arctic?
How long do polar stratospheric clouds typically last over Antarctica compared to the Arctic?
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What year did scientists publish their findings regarding the Antarctic ozone hole in 'Nature'?
What year did scientists publish their findings regarding the Antarctic ozone hole in 'Nature'?
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Study Notes
Ozone Hole Formation
- The ozone hole, a severe depletion of the ozone layer in the Antarctic stratosphere, is not caused by ozone-depleting substances being present throughout the stratosphere but by specific conditions unique to Antarctica.
- Low winter temperatures in the Antarctic stratosphere favor the formation of polar stratospheric clouds (PSCs).
- PSCs, combined with the isolation of polar stratospheric air in the polar vortex, create the perfect environment for chlorine and bromine reactions to deplete ozone.
Temperature Differences
- Antarctic minimum air temperatures are significantly lower than Arctic temperatures, reaching as low as -92°C in July and August, while Arctic minimum temperatures hover around -80°C in late December and January.
- PSC formation occurs at temperatures lower than -78°C, meaning it persists for about 5 months in Antarctica but only 1-2 months in the Arctic.
PSC Formation and Reactions
- PSCs consist of liquid and solid particles that form when stratospheric temperatures drop below -78°C.
- Reactions on the surfaces of these PSCs increase the abundance of chlorine monoxide (ClO), a highly reactive gas that catalytically destroys ozone.
- The abundance of ClO increases when reservoir forms of reactive chlorine gases, chlorine nitrate (ClONO2) and hydrogen chloride (HCl), are converted to ClO.
Isolation of Polar Stratosphere
- Strong winds encircle the polar regions during winter, forming a polar vortex that isolates the polar stratosphere from other regions, preventing mixing and transport of air.
- The Southern Hemisphere polar vortex is stronger than the Northern Hemisphere's, due to differences in land, ocean, and mountain distribution.
- Stronger vortexes lead to greater isolation and longer-lasting PSCs, which is why ozone depletion is more severe in the Antarctic.
Nitric Acid and Water Removal
- The descent of PSCs removes nitric acid (HNO3) from the stratosphere, a process called denitrification.
- Denitrification removes nitrogen oxides (NOx), which are important for converting ClO back into reservoir gases.
- This results in sustained high levels of ClO, enhancing ozone destruction.
- Ice particle formation also removes water vapor from the stratosphere, a process called dehydration.
- Dehydration indirectly affects ozone destruction by suppressing PSC formation later in the winter, thereby reducing ClO production.
The Role of PSCs
- The role of PSCs in ozone depletion wasn't fully understood until the discovery of the Antarctic ozone hole in 1985.
- Laboratory studies, computer modeling, and direct measurements confirmed the involvement of PSCs and ClO in ozone destruction.
The Discovery of the Antarctic Ozone Hole
- The first signs of Antarctic ozone depletion appeared in the early 1980s with ground-based observations.
- These observations revealed unusually low total ozone during late winter/early spring (September-November).
- Satellite measurements confirmed the ozone depletion and revealed that the depletion was centered near the South Pole.
- The term "ozone hole" was coined to describe the very low total ozone values observed in satellite images.
- Currently, the ozone hole is monitored by a combination of satellite, ground-based, and balloon observations.
Early Antarctic Ozone Measurements
- Early Antarctic ozone measurements in the 1950s showed lower ozone values than the Arctic, which was unexpected.
- These values were not anomalous, they were lower due to the stronger and colder Southern Hemisphere polar vortex.
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Description
Explore the fascinating science behind the formation of the ozone hole and the critical role polar stratospheric clouds (PSCs) play in this process. Learn how Antarctic conditions differ from the Arctic and how these variations affect ozone depletion. This quiz examines the specific temperature and chemical reactions that contribute to this environmental issue.
