1. Introduce students to the environmental factors that affect air quality.

Let students know that environmental factors affect the severity and duration of pollution events. Show the New Bridge in Bratislava on Clear Day photograph and the New Bridge in Bratislava with Temperature Inversion photograph. (Download the image by clicking on the down arrow in the lower right corner of the media carousel window.) Tell students that the temperature of the atmosphere affects the movement of pollutants. Ask:

• What happened to the temperature of the air between the first picture and the second picture? (There is a temperature inversion in the second picture. The air is cooler at the surface than it is above the surface. Normally, the air cools with increasing elevation.)

• What happened to change the temperature of the atmosphere? (A temperature inversion can be caused by cool air at the surface because of snow/ice on the surface or by cooler air blowing in off a colder body of water.)

2. Discuss the role of uncertainty in the scientific process.

Tell students that science is a process of learning how the world works and that scientists do not know the “right” answers when they start to investigate a question. Let students know that they can see examples of scientists' uncertainty in forecasting air quality. 

Tell students that air quality is measured by the Air Quality Index. Show students the Air Quality Index, which includes explanations of the ranges used in the air quality index. Then project the Forecast of Air Quality on December 10, 2013 image and Air Quality on December 10, 2013 image. (Click on the link in the media carousel above and download using the arrow in the lower right corner of the window.) Tell students that these are snapshots of the air quality forecast and the real-time air quality in the United States on December 10, 2013. Ask:

• Did the forecast accurately predict which areas would have poor quality air? (The forecast air quality overlaps with many of the poor air quality areas, but it does not cover all of them. The air quality in some areas [Northern California] is much worse than the forecast predicted.)

• Why do you think scientists did not accurately predict the air quality for more of the United States? (Student answers will vary. The air quality forecast is affected by human activities that may not be easily predicted.)

Tell students they will be asked questions about the certainty of their predictions. Let students know that they should think about what scientific data is available as they assess their certainty with their answers, and encourage them to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

3. Introduce the concept of stocks and flows in a system.

Tell students that materials flow into and out of systems. The flow of the materials over time can change and can be influenced by many different factors and interacting parts. Scientists think about how one part of the system can affect other parts of the system. Give students a simple example of a stock and flow in a system, as described in the scenario below.

There is a bathtub with water flowing in from the faucet and water leaving through the drain. Ask:

• When the drain is plugged, what happens to the level of water in the bathtub? (The water level will increase because the outflow of water is stopped, but water keeps coming in from the faucet.)

• When the faucet is turned off, what happens to the level of water in the bathtub? (The water level will decrease because the inflow of water is stopped, but the water keeps leaving through the drain.)

• How can the level of water in the bathtub be kept at the same level? (The water in the bathtub can be kept at the same level by making the inflow equal to the outflow. Then, the water that comes in through the faucet will be offset by the water that leaves through the drain.)

Tell students they will be following the flow of materials, in this case the amount of air pollution, in the system. Let students know they will be exploring some environmental and human factors that contribute to changes in the amount of pollution being added to and removed from the modeled system.

4. Introduce and discuss the use of computational models.

Introduce the concept of computational models, and give students an example of a computational model that they may have seen, such as forecasting the weather. Project the NOAA Weather Forecast Model, which provides a good example of a computational model. Tell students that scientists use models to predict future conditions based on current information about the energy and moisture in the atmosphere. Scientists use atmospheric models, such as these, to forecast where and when air quality may be bad.

5. Have students launch the Preventing Bad Air Days interactive.

Provide students with the link to the Preventing Bad Air Days interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to be able to share a computer work station. Tell students they will be working through a series of pages of questions related to the models in the activity. Ask students to work through the activity in their groups, discussing and responding to questions as they go.

NOTE: You can access the Answer Key for students' questions—and save students' data for online grading—through a free registration on the High-Adventure Science portal page.

Tell students this is Activity 6 of the Will the Air Be Clean Enough to Breathe? lesson.

6. Discuss the issues.

After students have completed the activity, bring the groups back together and lead a discussion focusing on the questions below.

NOTE: The answers provided are the correct answers; however, students should be encouraged to find these answers by using the models in the activity.

• What conditions created a thermal inversion in Model 4 (Model 4: Cross-Section of a City: With Thermal Inversion)? (The wind has to be coming from the water. The water is cooler than the land. The breeze coming off the water cools the surface of the land so it is colder than the layer of air directly above it.)

• Why are smog events longer-lasting when there is a temperature inversion? (Smog events are longer lasting when there is a temperature inversion because the temperature inversion prevents the air from rising through the atmosphere and dissipating over a larger area.)

• Can thermal inversions be prevented? (No, thermal inversions cannot be easily prevented. Thermal inversions are natural events. They are created when the surface is cooler than the air above. This can happen when there is snow on the ground, cooling the ground, while the Sun warms the air above it. They can also happen when cooler air blows off a large body of water onto the warmer land. The sea breeze [or lake breeze] cools the lower layer of air below the temperature of the air above.

• Is it more important to limit the pollution from cars or from power plants and factories (Model 5: Cross-Section of a City: With Pollution Control)? (The data from this model indicate that limiting vehicle pollution is more important to air quality than limiting power plant/factory pollution. This may or may not apply in the real world; the model's predictive power is limited because all car emissions are treated as the same, just as all power plant/factory emissions are treated as the same. The different types of pollutants emitted by the different pollution sources are not modeled with this model. The effect of weather is not modeled well enough to make long-term predictions about which pollution type has the biggest effect on the overall city pollution level. Pollutants from other power plants/factories could blow in to this area; only a small portion of the Earth is modeled in this model.)

• How can technology make a difference in air quality? (Technology can be developed that can lower the emissions of cars, power plants, and factories. Technology can also increase the efficiency of the polluting sources, meaning that there would be less pollution per mile traveled/unit of electricity generated/product manufactured. Technology can also create more pollution as a side effect of more manufacturing and more demand for products that pollute.)