Analyze and interpret quantitative data

Antarctic ozone and stratospheric chlorine

Unit 9
10 points
About 23 minutes

You can use a calculator on this question, just like on exam day.

You read values and trends from a data table or described graph, explain what the data show about an environmental problem, and propose and justify a solution. On the exam: Question 2 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question and its sources

Scientists measure the total ozone above Antarctica in Dobson units (DU) each spring. Table 1 shows the lowest October ozone value recorded in selected years and the estimated concentration of ozone-depleting chlorine in the stratosphere.

Table 1: Antarctic ozone and stratospheric chlorine

Year	Minimum October ozone (DU)	Stratospheric chlorine (parts per billion)
1975	285	1.8
1980	225	2.2
1985	170	2.7
1990	125	3.2
1995	100	3.6
2000	95	3.8
2005	100	3.7
2010	110	3.6
2015	115	3.5
2020	120	3.3

Source: Hypothetical data, simplified from the general pattern of Antarctic measurements

Suggested time: 23 minutes

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Part (a)

1 point

Identify the year in Table 1 when stratospheric chlorine was highest.

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Part (b)

1 point

Describe the trend in minimum October ozone from 1975 to 2000.

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Part (c)

1 point

Describe the relationship between stratospheric chlorine and minimum October ozone shown in Table 1.

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Part (d)

1 point

Identify the main human-made source of the chlorine that destroys stratospheric ozone.

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Part (e)

1 point

Explain how a single chlorine atom can destroy many ozone molecules.

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Part (f)

1 point

Identify the international agreement that is mainly responsible for the decrease in stratospheric chlorine after 2000.

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Part (g)

1 point

Use the data in Table 1 to explain why the recovery of the ozone layer has been slow.

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Part (h)

1 point

Describe one effect on human health of increased ultraviolet (UV) radiation reaching Earth's surface.

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Part (i)

1 point

CFCs were eventually replaced by hydrofluorocarbons (HFCs) in many refrigerators and air conditioners. Describe one environmental problem caused by HFCs.

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Part (j)

1 point

Propose one realistic way to reduce the release of HFCs into the atmosphere.

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