1. Activate students' prior knowledge about air movements in the atmosphere.

Show the Air Pollution From a Power Plant photograph. Tell students that pollutants emitted into the atmosphere do not stay in the atmosphere or even directly above the polluting source forever. They move throughout the atmosphere and are moved and removed by natural processes. Ask:

•  What natural process causes pollutants to move away from the pollution source? (Wind will cause pollutants to move away from the source.)

• What natural process would remove pollutants from the atmosphere? (Precipitation would remove pollutants from the atmosphere.)

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 Movement of Pollutants interactive.

Provide students with the link to the Movement of Pollutants interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to share a computer workstation. Tell students they will be working through a series of pages of models with questions related to the models. Ask students to work through the interactive 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 that this is Activity 3 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 these questions:

• What conditions allow for the best air quality over the city in the model (Model 2: Cross-Section of a City: With Graph)? (In the city in the model, the best air quality is achieved when the wind is blowing toward the water or when it rains frequently.)

• How did you get poor air quality over the city in the model (Model 2: Cross-Section of a City: With Graph)? (Poor air quality can result when the wind is blowing towards the mountains, when there is infrequent rain, and when there is infrequent rain and intense sunlight.)

• Where did you put factories in Model 3 so that all the cities had good air quality (Model 3: Satellite View of a City)? (Factories should be placed south of the northeastern-most mountains so that the wind won't blow the pollutants to City A. The wind from the northeast or east will not blow pollutants into any city when the factories are located directly south of the northeastern-most mountains.)

• How can pollution from Asia affect North America? (The wind blows primarily from the West. Polluted air over Asia can be blown across the ocean to affect cities in North America.)

• How could tall buildings affect a city's air quality? (Tall buildings could form a barrier to pollutants' escape from the area. This is dependent on the wind direction.)

• Mexico City, Mexico is surrounded by mountains on all sides. How does this affect the region's air quality? (The air quality could be affected by the mountains because the pollution might not be able to rise up over the mountains and blow away. This could make the air quality in the city quite poor.)