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Hot Blacktop: Monitoring and Cooling a Schoolyard

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Hot Blacktop: Monitoring and Cooling a Schoolyard

Use sensor data to measure how paving heats a schoolyard, then judge ways to cool it.

Monitoring the heat

Read the passage and Table 1, then answer the questions.

The Schoolyard Heat Study

1Palo Seco Middle School is in a desert city in the southwestern United States. The school and its numbers are made up, but they are based on real measurements in hot, sunny cities. The school's weather club keeps a weather station on the roof and checks a forecast app each morning. Last September, the app showed a heat warning on 9 school days, and the nurse saw several students with red, sore hands after they fell on the blacktop play area.

2When people replace soil and plants with pavement and roofs, they change the land's surface. Dark pavement absorbs most of the sunlight that hits it, gets very hot and warms the air above it. Plants and moist soil stay cooler, because water evaporating from leaves and soil carries energy away, and trees also shade the ground. Hot pavement keeps giving off heat after sunset, so the air near it can stay warm at night. A city that is warmer than the land around it is called a heat island.

3Club member Zofia Benally and her teammates set up four sensor stands around the schoolyard, at sites with different surfaces. At each stand, they measured the surface temperature with an infrared thermometer and the air temperature 1 m above the ground inside a white, shaded shield. They took readings at 3 p.m. and at 5 a.m. on five sunny days in September and found the average of each set.

4The principal, Dr. Marguerite Osei, asked the club to help choose a way to cool the 2,000 m² play area. The school set three requirements. By next September, the play area's 3 p.m. surface reading on sunny days must be 45 °C or less. The project must cost $65,000 or less. It must use no extra city water. The club tested each idea on a small patch of blacktop and estimated the cost for the whole area. Young trees grow slowly, so their patch reading is what the club expects next September; full shade would take about 10 years.

Table 1. September Averages, Five Sunny Days
SiteSurfaceSurface, 3 p.m. (°C)Air, 3 p.m. (°C)Air, 5 a.m. (°C)
A. Play areaBlack asphalt, full sun624029
B. Gravel gardenGravel and shrubs, sun513826
C. Sports fieldWatered grass, full sun373724
D. Tree groveBare soil, tree shade343625
1.

At 3 p.m., the play area's surface was °C hotter than the sports field's surface, but the air above it was only °C warmer.

2.
Which statement best describes Table 1?
Question 2 options
3.
Use paragraph 2. Why was the air at the play area still the warmest at 5 a.m., long after sunset?
Question 3 options
4.
Why did the club use the same kind of sensor stand, the same times of day and only sunny days at all four sites?
Question 4 options
5.
Underline each piece of evidence that paving the play area changed the schoolyard's local environment.

Choosing a design

Use Table 2 and the three requirements in paragraph 4.

Table 2. Test Patches and Cost Estimates
IdeaSurface, 3 p.m. (°C)Cost, whole area ($)Extra city water?
Plain blacktop (no change)620No
1. Light-colored cool coating5030,000No
2. Shade sails over the area3860,000No
3. Shade sails plus cool coating3590,000No
4. Replace with watered grass3650,000Yes
5. Young trees in planters5520,000No (rain tank)
6.
Use paragraph 4 and Table 2. Sort each idea. Each idea that misses fails only one requirement.
7.

Compared with plain blacktop, the shade sails cooled the patch's surface by °C. Adding the cool coating under the sails cooled it °C more, for an extra cost of $.

8.
A parent group gives the school $25,000, so the budget grows to $90,000. The other two requirements stay the same. Which idea now meets every requirement and gives the coolest surface?
Question 8 options
9.
What is the main drawback of Idea 5, the young trees, for this year's goal?
Question 9 options

Did the sails work?

The school chose Idea 2. The next September, the club repeated its 3 p.m. surface readings on five sunny days.

Table 3. 3 p.m. Surface Readings, Sunny-Day Averages (°C)
SiteSeptember beforeSeptember after
A. Play area (sails added)6237
B. Gravel garden (no change)5148
C. Sports field (no change)3734
10.
Dr. Osei says, "The sails cooled the blacktop surface by 25 °C." Which response do the data in Table 3 support best?
Question 10 options
11.
A parent says, "Blacktop only matters for the few seconds when a kid touches it. It does not change the schoolyard's environment." Do you agree? Write a claim, use at least two pieces of data from Table 1 or Table 3 as evidence, and explain your reasoning.