| YES | if the statement agrees with the views of the writer |
| NO | if the statement contradicts the views of the writer |
| NOT GIVEN | if it is impossible to say what the writer thinks about this |
Will Antarctic Ozone Bite the Dust?
This year’s ozone hole above Antarctica may be deeper than ever as a result of the eruption of Mount Pinatubo. This is the conclusion of researchers who have combined observations of the effect of debris from the eruption on the stratosphere with the latest measurements of stratospheric ozone over the equator and the Antarctic.
A team led by W. B. Grant of the NASA Langley Research Center in Hampton, Virginia, monitored the influence of Mount Pinatubo, in the Philippines, before and after its eruption last June, using balloon-borne instruments launched from Brazzaville in the Congo (4 South, 15 East) and Ascension Island (8 South, 14 West).
The scientists found that most of the volcanic material injected into the stratosphere settles out at a height of between 18 and 28 kilometres, with the greatest concentrations between 24 and 25 kilometres. At precisely these altitudes, the amount of ozone in the stratosphere declined between three and six months after the eruption. The greatest loss — of 20 per cent — was at an altitude of 24 kilometres (Geophysical Research Letters, Vol. 19, p.1109).
The loss of ozone at a height of between 16 and 28 kilometres was between 13 and 20 Dobson units — about 5 per cent. There was a slight increase in the ozone concentration above 28 kilometres, but the researchers could not measure ozone beyond 31 kilometres because their balloons burst.
Grant and his team suggest that reactions in the stratosphere involving the Pinatubo material release chlorine in the active form which destroys ozone. Stratospheric chlorine originates chiefly from the manufactured compounds known as CFCs, but is usually locked up in stable form as chlorine nitrate. In the presence of sulphuric acid droplets from Mount Pinatubo, ozone-destroying chlorine monoxide is released.
Chlorine monoxide, which is produced by a similar series of reactions involving icy particles in the stratosphere, is blamed for the springtime depletion of ozone above Antarctica. In 1991, this depletion was as severe as in any year since the discovery of the ozone hole in the early 1980s, according to B. L. Johnson, T. Deshler and R. A. Thompson of the University of Wyoming, Laramie. Balloon flights from McMurdo Station, which lies at 78 South, revealed severe ozone depletion in October 1991 at altitudes between 12 and 20 kilometres with a 93 per cent loss of ozone between 17 and 18 kilometres.
The minimum amount of ozone above McMurdo, reached on 10 October 1991, was 146 Dobson units — almost exactly the same as the minimum reached in 1987 and 1990. The figure for the column between 12 and 20 kilometres altitude was a record low of 18 Dobson units, representing a loss of 83 per cent of the ozone in that layer.
“The 1991 volcanic eruptions will substantially increase the aerosol loading within the polar vortex for 1992, both below and above 20 kilometres," the team predicts. “These extra particles may enhance the heterogeneous reactions, leading to ozone destruction, and this ozone depletion above Antarctica may worsen in 1992 by spreading to altitudes beyond the 12 to 20 kilometres layer.”
AI explanationShows the answer. Tap to open.
Question Focus: Writer opinion supported by scientific explanation of cause of ozone destruction.
Correct Answer: YES
Why this is correct: The writer clearly supports this view by explaining the mechanism. The sentence directly says that chlorine in the active form destroys ozone, which shows agreement with the statement.
Passage Reference: Grant and his team suggest that reactions in the stratosphere involving the Pinatubo material release chlorine in the active form which destroys ozone. Stratospheric chlorine originates chiefly from the manufactured compounds known as CFCs, but is usually locked up in stable form as chlorine nitrate.
Common Mistake: Answering NOT GIVEN because the student thinks this is only a fact. This is a Paraphrase trap because the statement repeats the writer's explanation using slightly different words.
Paraphrasing: Passage: 'chlorine in the active form which destroys ozone' = Statement: 'Ozone is destroyed by chlorine in the active form'
Tips: When the writer explains a cause using confident language, that usually shows agreement, not just a neutral fact.
Key Vocabulary:
- active form = chemically reactive state
- destroys = breaks down
Question Focus: Writer disagrees by blaming a different substance for ozone depletion.
Correct Answer: NO
Passage Reference: Stratospheric chlorine originates chiefly from the manufactured compounds known as CFCs, but is usually locked up in stable form as chlorine nitrate. In the presence of sulphuric acid droplets from Mount Pinatubo, ozone-destroying chlorine monoxide is released. Chlorine monoxide, which is produced by a similar series of reactions involving icy particles in the stratosphere, is blamed for the springtime depletion of ozone above Antarctica.
Why this is correct: The writer clearly says that chlorine monoxide, not chlorine nitrate, is responsible. Chlorine nitrate is described as a stable form, so the statement contradicts the writer's view.
Common Mistake: Answering YES because both substances contain chlorine. This is a Contradiction trap because the passage names a different chemical as responsible.
Paraphrasing: Passage: 'chlorine monoxide is blamed for the springtime depletion' = Statement: 'chlorine nitrate was responsible for the springtime depletion'
Tips: Check carefully which substance the writer blames. Similar scientific words often hide a contradiction.
Key Vocabulary:
- responsible for = causes
- depletion = reduction
Question Focus: Prediction by scientists clearly stated and supported.
Correct Answer: YES
Passage Reference: 'The 1991 volcanic eruptions will substantially increase the aerosol loading within the polar vortex for 1992, both below and above 20 kilometres," the team predicts. 'These extra particles may enhance the heterogeneous reactions, leading to ozone destruction.
Why this is correct: The writer reports the scientists' prediction using strong language like will substantially increase, which shows clear support for the statement.
Common Mistake: Answering NOT GIVEN because it refers to the future. This is a Time/tense trap because predictions are still the writer's reported view.
Paraphrasing: Passage: 'will substantially increase the aerosol loading within the polar vortex' = Statement: 'will increase substantially because of the 1991 volcanic eruptions'
Tips: Predictions count in YNNG. If the writer reports them clearly, you can answer YES or NO.
Key Vocabulary:
- substantially = by a large amount
- aerosol loading = amount of particles in the air
Question Focus: Writer reports the opposite prediction about future ozone levels.
Correct Answer: NO
Passage Reference: 'These extra particles may enhance the heterogeneous reactions, leading to ozone destruction, and this ozone depletion above Antarctica may worsen in 1992 by spreading to altitudes beyond the 12 to 20 kilometres layer.'
Why this is correct: The writer says ozone depletion may worsen, which is the opposite of improve. This shows clear disagreement with the statement.
Common Mistake: Answering NOT GIVEN because the student misses the word 'worsen'. This is a Reverse meaning trap.
Paraphrasing: Passage: 'ozone depletion above Antarctica may worsen in 1992' = Statement: 'ozone depletion over Antarctica may improve in 1992'
Tips: Always check direction words like improve, worsen, increase, decrease. One word can flip the answer.
Key Vocabulary:
- worsen = get worse
- improve = get better
General Tips:
- YNNG tests the WRITER'S VIEW, not just scientific facts. Look for blame, predictions, and judgments.
- YES and NO both need clear writer opinion. If the writer is silent about the view, choose NOT GIVEN.
- Statements follow passage order, so scan forward from the last answer.
- Be careful with scientific terms that sound similar. This is a common contradiction trap.
- Watch for future predictions. Words like 'will' and 'may' often signal the writer's position.
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