Air pollution can be reported in several ways: concentration (amount of material in a volume of air in ppm or ppb), mass (weight of material in air in micrograms per cubic meter), or an Air Quality Index (AQI). The AQI is an index from 0 to 500 for reporting daily air quality based on human health considerations.

The U.S. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: groundlevel ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established National Ambient Air Quality Standards (NAAQS) to protect public health (see teacher resource on National Ambient Air Quality Standards.) The AQI is not a “standard,” but it is related to air quality standards. Note that the AQI is calculated hourly and is derived from data that have not been quality assured.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy—at first for certain sensitive groups of people, then for everyone as AQI values get higher.

To make it easier to understand, the AQI is divided into six categories and a specific color is assigned  to each AQI category. For example, the color  orange means that conditions are “unhealthy for sensitive groups,” while red means that conditions may be “unhealthy for everyone,” and so on.  There are different health messages for each of the AQI pollutants.

The six levels of health concern and what they mean are:

•      “Good” (Green): AQI between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.

•      “Moderate” (Yellow): AQI between 51 and 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people (extremely sensitive people).

•      “Unhealthy for Sensitive Groups” (Orange): AQI between 101 and 150. These groups include people with asthma, children and teens, the elderly, and people who work or exercise outside strenuously. People with lung disease are at greater risk from exposure to ozone, while people with either lung disease or heart disease are at greater risk from exposure to particle pollution. The general public is not likely to be affected when the AQI is in this range.

•      “Unhealthy” (Red): AQI between 151 and 200. The air is unhealthy for everyone and members of sensitive groups may experience more serious health effects.

•      “Very Unhealthy” (Purple): AQI between 201 and 300. Everyone should reduce and sensitive groups should avoid prolonged or heavy outdoor exertion.

•      “Hazardous” (Maroon): AQI over 300. Everyone should avoid all outdoor exertion.

In Michigan, ozone and fine particles are usually the pollutants that cause the AQI to be elevated. Newspapers, radio, television, and web sites report the daily AQI levels. The daily AQI for Michigan is posted on the MDEQ web site at http://www. deqmiair.org. That site has specific information about the actual values of pollutants at air monitoring stations and details of the air quality forecast. Maps from the U.S. EPA’s AIRNow site are particularly useful for identifying ozone patterns. These maps and AQIs for the whole country can be found at http://www.airnow.gov.

MDEQ meteorologists predict when conditions are favorable for excessive fine particle or ozone formation. Weather conditions conducive to ozone formation are high temperatures, high pressure, clear skies, and no wind. Low-pressure systems tend to dissipate the ozone. Inversions (atmospheric temperature increase with height) can trap pollutants, compounding the problem. High pollutant concentrations upwind can be transported into a different area and can cause substantial increases in air pollution that would not have otherwise occurred. An Action Day is called when weather conditions are likely to combine with pollution to create elevated amounts of ground-level ozone.

The Southeast Michigan Council of Governments and the Clean Air Coalition of Southeast Michigan (http://www.semcog.org) as well as the West Michigan Clean Air Coalition (http://www.wmcac. org/) operate local action programs to disseminate the air quality forecast message to communities. They encourage individuals and companies to make clean air choice on Action Days. Ozone Action and Clean Air Action are voluntary emissions reduction initiatives. These organizations provide teacher resources and tip cards for appropriate actions when DEQ meteorologists announce Action Days.  

The UV Index is a next-day forecast of the amount of skin-damaging UV radiation expected to reach the Earth’s surface at the time when the sun is highest in the sky (solar noon). The amount of UV radiation reaching the surface is primarily related to the elevation of the sun in the sky, the amount of ozone in the stratosphere, and the amount of clouds present. The UV index is a good way to link stratospheric ozone depletion with human health effects. The Index predicts UV intensity levels on a scale of 1 to 11+, where low indicates a minimal risk of overexposure and 11+ means an extreme  risk. Calculated on a next-day basis for every zip code across the United States, the UV Index takes into account clouds and other local conditions  that affect the amount of UV radiation reaching  the ground in different parts of the country. 

The UV index can be found as a link from  http://www.epa.gov/sunwise/uvindex.html

Sources:

Michigan Department of Environmental Quality. Air Quality

U.S. Environmental Protection Agency. AIRNow. 

Retrieved April 1, 2005 from http://www.epa.gov/airnow

Division. Michigan’s Air. Retrieved April 1, 2005, from  http://www.michigan.gov/deqair/

U.S. Environmental Protection Agency. What Is the UV Index? Retrieved April 1, 2005, from  http://www.epa.gov/sunwise/uvwhat.html

1.   Introduce the Air Quality Index (AQI).

What do the colors in a stop light mean for people’s behavior? [Red means stop, yellow means caution, and green means go.] Tell students that they will be learning about the air quality index, which also uses colors. Using different colors of construction paper to represent the AQI colors as presented in the teacher background material, have students rank the colors from good to poor air quality. Have students read the information from the Michigan Department of Environmental Quality and the Department of Community Health on The Air Quality Index. Explain that the AQI itself is not an air quality standard. Also stress that when two or more criteria pollutants are monitored at one location, the highest value (worst air measured) drives the AQI value. High AQI values in summer are often from ozone and high AQI levels in winter are from particle pollution.

Optional: The Interpreting the AQI student activity page can be used to practice AQI interpretation.

What is your local AQI and how does it compare to other sites in Michigan and the United States? Use the What Is Your AQI? student pages to find the daily AQI, the AQI for ozone (only between May and September), and the AQI for particle pollution (year around).

Explore actual particle pollution and ozone episodes by graphing hourly values on the Patterns of Particle Pollution and Ozone student activity page either through AIRNow animated maps or using actual values. Information about what was actually happening in these episodes is found in the teacher resource on the Particle Episode, January 31-February 6, 2005 and the Case Study of the June 22-28 PM₂₅ and Ozone Episodes in the Midwest and the United States found on the MEECS Air Quality CD.

 Non-Internet based option for students: Prior to class, check the MDEQ and EPA web sites for the latest AQI readings and provide the information to the students.

The data shown on the Patterns of Particle Pollution and Ozone student data sheet can be used to generate the time series chart without using the computer. 

3.      Test a hypothesis about the AQI using web sites (Lesson Extension).

Is the Air Quality Index (AQI) the same throughout Michigan? Does the AQI change with time? With the types of pollutants measured? Are ozone levels higher in the Upper Peninsula than in lower Michigan? Use the Tracking the AQIstudent activity pages to answer questions such as these using the scientific method. Help students formulate a question concerning air quality in Michigan. Next help them develop a reasonable hypothesis that can be tested using information from the MDEQ web site. Encourage students to find data that are relevant to their question so that they have a solid basis for their conclusions.

Non-Internet based option for students: Materials on the MEECS Air Quality CD include archived ozone and particle pollution maps, air quality forecasts, and forecast maps that could be reproduced in alternate forms.

4.      Explore the relationship between the AQI and weather using web sites or newspapers (Lesson Extension).

Is the Air Quality Index (AQI) related to weather conditions? Brainstorm ways that the weather conditions might affect air quality and list them on the board and on the student activity page, The AQI and Weather. In small groups have the students construct a reasonable hypothesis concerning weather and the AQI. Guide the students to testable hypotheses based on the data available at the DEQ web site.

Students collect information from the weather forecast to predict the AQI for the next day. For ozone formation, some important weather factors are amount of sunlight, wind speed and direction, and temperature. Consult actual daily forecasts for the AQI by MDEQ meteorologists at the MDEQ web site. These can be compared to student forecasts. Finally, confirm the actual AQI from the MDEQ web site. Have students present the results of their research to the class.

 Non-Internet based option for students: Use the data from Weather Conditions and the Air Quality Index (AQI) for an Ozone Episode student resourceas a basis for hypothesis testing. Some newspapers carry a weather forecast with a corresponding AQI and UV index.

5.      Determine the UV Index and its importance (Optional).

What is the UV Index? Now that the AQI has been explored, students can be introduced to the UV index. Have them read The Ozone

Layer and the UV Index and show them the UV

Index PowerPoint slides on the Air Quality CD. Guide a discussion to reinforce the link between stratospheric ozone depletion and UV radiation.

Why is the UV Index important? Brainstorm answers to this question and record them on the student pages, Tracking the UV Index. Use the Internet site, http://www.epa.gov/sunwise/index. html, to access data for your zip code. Record daily UV Index numbers and data for one week. If you are able, note changes in the UV Index throughout the week and as weather conditions change. Discuss reasons for these changes and how they affect exposure to UV radiation.

Optional: Interpreting the UV Index student activity page can be used to practice UV Index interpretation.

6.   Tying it all together.

Why is knowing about air quality important? Draw on the students’ knowledge about pollutants and health effects. Show the PowerPoint on Air Pollution—Michigan on the MEECS Air Quality CD as a review of the lesson and material covered in the unit so far.

Return to the demonstration using different colors of construction paper and solicit ideas about what these colors mean in terms of AQI levels and health.