Analyze and interpret quantitative data

Ozone over a city on a summer day

Units 7 and 8
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

An air-quality station in a large, sunny city measured three pollutants every two hours on a hot, windless summer day. Most of the city's workers commute by car.

Table 1: Air pollutant concentrations through the day (parts per billion, ppb)

Time	Nitrogen monoxide, NO (ppb)	Nitrogen dioxide, NO₂ (ppb)	Ground-level ozone, O₃ (ppb)
6 AM	20	18	10
8 AM	65	30	12
10 AM	35	55	35
12 PM	15	40	70
2 PM	8	25	95
4 PM	10	22	88
6 PM	30	28	55
8 PM	25	30	25

Source: Hypothetical data

Suggested time: 23 minutes

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Part (a)

1 point

Identify the time of day when NO was highest.

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Part (b)

1 point

Explain why NO is highest at that time of day.

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Part (c)

1 point

Describe the change in ground-level ozone from 8 AM to 2 PM.

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Part (d)

1 point

Explain why ground-level ozone peaks in the afternoon rather than during the morning rush hour.

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Part (e)

1 point

Identify whether ground-level ozone is a primary or secondary pollutant, and justify your answer.

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Part (f)

1 point

Explain why ozone concentrations fall between 4 PM and 8 PM.

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Part (g)

1 point

Describe one effect of ground-level ozone on human health.

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Part (h)

1 point

Describe one way a catalytic converter in a car's exhaust system reduces the formation of ground-level ozone.

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Part (i)

1 point

Propose one realistic action the city could take to reduce photochemical smog, other than requiring catalytic converters.

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Part (j)

1 point

Use the data in Table 1 to justify the action you proposed in part (i).

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