Adapted with permission from NASA Aura Education and Public Outreach.
To measure ozone in the Earth's atmosphere, NASA built the approximately 6,500-pound Aura satellite. The spacecraft carries four high-tech instruments that scan the globe from more than 700 kilometers above the planet.
For students, there is an easy way to investigate ozone in their own neighborhood. It's as simple as growing a few carefully selected plants. Teams of scientists and educators at NASA are showing how this can be done. They have installed ozone-monitoring gardens at several NASA centers.
Ozone, a molecule made up of three oxygen atoms, can be both good and bad, depending on its location. It's good to have ozone high up in the atmosphere - in the stratosphere - where it occurs naturally and protects humans and other living things from the sun's harmful ultraviolet rays. It's bad to have ozone in the lower atmosphere - in the troposphere - where it forms when pollution from cars, factories, and other manmade sources interacts with sunlight.
Too much tropospheric ozone makes air unhealthy for people to breathe. Some plants are also sensitive to ozone, which enters plants through tiny pores in a leaf's outer layer. When exposed to high levels of the gas for extended periods of time, leaves on these sensitive plants develop tiny, colored, evenly spaced spots. The leaves may also turn yellow, and reduced photosynthesis may hinder overall plant growth.
NASA's ozone gardens contain several types of ozone-sensitive plants: cut-leaf coneflower, flowering dogwood, buttonbush, snap beans, soy beans, and milkweed. Students can monitor local ozone by looking in their neighborhoods for ozone-injured plants or establishing similar gardens outside their schools or in their backyards.
- Computer with Internet access
- Plants native to your area
- Gardening tools (shovel, etc.)
- First, make observations of ozone injury in your neighborhood. The best observation times for ozone injury are during the summer months (May through September in the northern hemisphere) when sunlight is most intense, and high levels of surface ozone typically occur.
- Identify plant species. Not every species is sensitive to ozone, and some are more sensitive than others. Even within a species, varieties may differ in their ozone sensitivity.
- Check this list of ozone-sensitive species for your plant: www.nature.nps.gov/air/Pubs/bioindicators/index.cfm.
- Carefully examine the bottom (older) leaves on the plant for ozone injury. Ozone injury appears as tiny light-tan to reddish-purple spots or "stippling" on the top surface of the leaf only.
- If any leaf injury crosses over the veins or veinlets of the leaf, it is due not to exposure to ozone, but to some other cause.
- Next, prepare to plant your own ozone garden. Determine the size of your garden. How much space do you have? Ozone gardens can range from a single plant in a pot to a yard full of ozone-sensitive species.
- Select a location where it is permissible to plant your garden. Determine the hours of direct sunlight needed for the species you plan to grow and site your garden accordingly. Locations that are downwind of heavy traffic or other pollution sources are likely to have more ozone than locations that are behind belts of trees or open green spaces. Make sure you have a nearby source of water and somebody to keep the garden watered once or twice a week if you cannot do it yourself.
- Choose which plants to keep in your garden. Plants that are native to your geographic location will most likely be the most successful. Start by identifying native plants in your area, perhaps by searching the Internet.
- Plant your garden and watch your plants grow! Start watching for signs of ozone injury as soon as your plants begin to sprout leaves.
- As growing season progresses, keep a watchful eye on your plants. The recommended minimum observation period is two weeks. The more you check your plants, the more detailed information you will gather on your plants' progression.
For more, go to http://aura.gsfc.nasa.gov/outreach/ozonegarden.html and http://ozonegarden.larc.nasa.gov.