Center for Innovation in Engineering and Science Education
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Is Your Bus Exhausting? Stevens Institute of Technology



Smog City is an interactive air pollution simulator that demonstrates how personal choices, environmental factors, and land use can contribute to air pollution. While using the Smog City application, the user is in control so the “visit” can be a healthy or unhealthy experience. Users can see how ground level ozone, the biggest part of summertime smog, increases or decreases depending on the time of day in Smog City. Since ozone can irritate respiratory systems, cause breathing difficulty, coughing, and chest pain, knowing how and why ozone forms and what can be done is important to the residents of Smog City and everyone else on the planet.

Cautionary Note: Relationships between ozone, emissions, and weather conditions are very complex. Smog City's relationships are based on a simplified model of complex atmospheric processes in Sacramento, California, therefore there is no guarantee that the model is scientifically accurate for this or other regions. Results only illustrate general behavior of air pollution processes, and cannot be used for any quantitative purpose or in detailed planning of future control strategies.

Ozone levels depicted in Smog City are estimated by simulating the air quality over Sacramento, California using a computerized model of the region. The computer model creates an imaginary box over the area to represent the atmosphere above Sacramento. Air quality conditions in the box are simulated to account for both human influences and natural factors that affect ozone formation. Each simulation represents one day. In the morning, the box has healthy air quality conditions. As each hour of the day passes, pollutants from human activities such as industry and operating cars and trucks, are released into Smog City's atmosphere. In this model, pollutants take into account variations in human activity, such as morning rush-hour traffic and movement and mixing, which are influenced by weather characteristics such as wind speed, sunlight, and temperature.

One weather characteristic that can have influence over ground level ozone production is the presence of a temperature inversion layer.  Temperature inversion layers typically form when the temperature of the ground rapidly decreases as the sun sets in the evening. The cooling of the ground subsequently cools the air directly above it. This cool layer of air is heavier than the warmer air above, causing the cool air to become trapped close to the ground. This is the opposite of what normally occurs, air temperature decreasing with altitude, so it is called an inversion.  Temperature inversion layers can occur between 100 to a thousand feet above the ground depending on the weather conditions. Inversions act like a cap on the atmosphere causing air pollutants from human activities to build up in the cool air trapped under the inversion layer, resulting in an increase of air pollution levels. In some places when there is little or no wind, inversion layers can linger for several days.

The development of Smog City was a collaborative community outreach effort between public agencies and private sector consultants. Funded by a grant from the U.S. Environmental Protection Agency, Smog City is a copyright of the Sacramento Metropolitan Air Quality Management District. Smog City is authorized for use as an educational and demonstration tool and may be downloaded for non-profit use by the general public, other agencies, associations, and educational institutions. Smog City: Copyright 1999 Sacramento Metropolitan Air Quality Management District.

In this lesson, students will create their own investigation using the ozone modeling tool. For the investigation, the student must create a hypothesis, design the experiment, run the experiment and discuss the results. The Procedure section contains directions for using the Smog City model.

For additional information about the scientific method and the importance of controls in an experiment, view The Principles of Science example.


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