Mapping Troposhperic Ozone Levels Over Time

Objective

The goal of this project is to investigate ozone levels over time using archived data for the United States from the AIRNow website.

Introduction

Ozone (chemical formula: O₃) occurs naturally in the upper atmosphere (stratosphere). It absorbs potentially harmful ultraviolet radiation from the sun that would otherwise reach the earth's surface. Ozone in the stratosphere thus serves a protective function for life on earth.

In the lower atmosphere (troposphere) ozone is produced by chemical reactions from nitrogen oxides (NO_x, chemical compounds with various ratios of nitrogen and oxygen) and volatile organic compounds (VOCs). A compound is said to be "volatile" if it evaporates readily at normal outside temperatures. Both heat and sunlight are also required for the chemical reactions that produce ozone. Nitrogen oxides are produced in exhaust from factories, power plants, cars, and trucks. Chemical solvents and gasoline vapors are major sources for volatile organic compounds in the atmosphere (AIRNow, 2007a).

Ozone is a highly reactive form of oxygen. The oxygen that we use for respiration (chemical formula: O₂) is less reactive. Ozone can more readily form compounds with an unpaired electron in the outermost shell. These compounds, called free radicals, can cause chain reactions that cause indiscriminate damage to molecules in cells. Virtually any large molecule in the cell—proteins, carbohydrates, lipids, and DNA—can be damaged by free radicals. Enzymes (catalase, superoxide dismutases, and glutathione peroxidases) and anti-oxidant molecules from the diet (e.g., vitamins C and E) act as free radical scavengers, and protect cells from damage caused by free radicals.

Since ozone formation in the troposphere requires heat and sunlight, ozone levels are more likely to rise when the temperature is high. However, other conditions, such as an increase in the pollutants from which ozone is formed, can also lead to ozone elevation. In this project, you can use map data from the U.S. Environmental Protection Agency and other government agencies (AIRNow, 2007c) to track ozone levels in your area under different seasonal conditions to find out when ozone levels are most likely to be elevated.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

Ozone
Nitrogen oxides (NO_x)
Volatile organic compounds (VOCs)
Troposphere
Stratosphere
Electron
Electron shells
Free radical
Parts per billion (ppb)
Air Quality Index (AQI)

Questions

Why is ozone in the stratosphere protective?
Why is ozone in the troposphere harmful?
How does ozone form in the troposphere?
What conditions make ozone more likely to form?

Bibliography

The AIRNow website has a page designed for students. Among other resources, you can find Flash animations on how ozone is formed, how ozone acts as a protectant high in the atmosphere but as a pollutant at ground level, and the sources and dangers of particle pollutants:
AIRNow, 2007a. "AIRNow—Air Quality Students," AIRNow, a cross-agency U.S. Government website [accessed April 20, 2007] http://airnow.gov/index.cfm?action=airnow.student.
A map of the current Air Quality Index for the continental U.S. can be found at:
AIRNow, 2007b. "AIRNow National Overview," AIRNow, a cross-agency U.S. Government website [accessed April 20, 2007] http://airnow.gov/index.cfm?action=airnow.main.
Maps of ozone levels for states and local regions can be found at:
AIRNow, 2007c. "Air Quality Maps," AIRNow, a cross-agency U.S. Government website [accessed April 20, 2007] http://airnow.gov/index.cfm?action=airnow.currentmaps.
For information on the effects of ozone on people, animals, and plants, see:
- Allen, J., 2002. "The Ozone We Breathe," NASA Earth Observatory Reference [accessed April 20, 2007] http://earthobservatory.nasa.gov/Library/OzoneWeBreathe/.
- AIRNow, 2007d. "Ozone and Your Health," AIRNow, a cross-agency U.S. Government website [accessed April 20, 2007] http://airnow.gov/index.cfm?action=static.brochure.
- For information on how atmoshperic ozone is monitored, see:
  Allen, J., 2003. "Watching Our Ozone Weather," NASA Earth Observatory Reference [accessed April 20, 2007] http://earthobservatory.nasa.gov/Library/OzoneWx/.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

Computer with Internet connection
Color printer

Experimental Procedure

Obtaining Air Quality Data

Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
To examine ozone levels for a U.S. state or local region, go the AIRNow Air Quality Maps webpage (AIRNow, 2007c).
Click on your state of interest, or select it from the drop-down list.
Next, you'll see an interface like the one below, which you can use to select a local region within a state (if available), and a date for viewing ozone map data. In the example below, we are choosing to examine data from "San Francisco Bay Area" region within California.
Make your selections for local region (if any) and desired date from the drop-down lists. Use the check boxes to select which maps you want, then click on the "Display Maps Below" button to show the mapped data.
A convenient way to scan several weeks' worth of data is to use the "Switch to Monthly Thumbnail Overview" option.
With the monthly thumbnails, you can scan several weeks' worth of data, and select dates of interest to see maps at higher resolution. Click on any of the thumbnail maps to see the data at full size.
The image below shows an example of a 1-Hour Average Peak Concentration map. The data is from the San Francisco Bay Area, for July 21, 2006. The map shows the highest concentration of ozone for each monitoring area during the course of the day. The legend for the colors used on the map is shown at right. The peak for each area can occur at a different time of day, so the data is not necessarily from any single time point during the day. You can also see an 8-hour average, or you can view an animated loop of time points throughout the day.
The Variations section has ideas for comparisons you could investigate with map data.

Variations

Are there seasonal variations in ozone concentrations? For example, you could compare ozone levels in winter months vs. summer months.
Sometimes the local climate can vary markedly within a small geographic area. For example, in the San Francsico Bay Area (see the map, above) there are dozens of local microclimates. You have the Pacific Ocean, the San Francisco Bay, and coastal mountain ranges all in close proximity. The air tends to be cooler near the ocean and the bay, and rises rapidly in summer months as you move inland. What effect(s) do you see in your area that may be attributable to local variations in elevation and/or bodies of water?
Do research on the sources of pollutants that form tropospheric ozone: nitrogen oxides (NO_x) and volatile organic compounds. Are ozone precursors produced in higher amounts on weekdays vs. weekends? Compare weekend data with weekday data to see if you can find consistent differences in ozone levels.

Credits

Andrew Olson, Ph.D., Science Buddies