Ozone: Friend and Foe
Does your city or town have "bad air" days in the summertime? Are you reminded to wear sunscreen when you go out to play? The same gas -- ozone -- that is the main factor in bad air also protects us from the Sun's harmful effects. How can one gas be both good and bad?

Image to left: Illustration of the Aura satellite, as it will appear in orbit 700 kilometers (435 miles) above Earth. Credit: NASA

Ozone is a gas that occurs naturally in very, very small amounts in the Earth's atmosphere. But human beings make extra ozone every day. Ground-level ozone is formed when exhaust from cars, trucks, factories and lawn mowers interact with sunlight, especially in the late spring and summer. When ozone is close to the ground, it can irritate lungs and trigger asthma attacks. Some communities offer free bus rides, encourage carpooling and ask people to wait until evening to mow lawns or fill gas tanks on high ozone days.

But we wouldn't want to get rid of ozone entirely. Ozone is our protection from the Sun's ultraviolet (UV) light, which can cause sunburn, skin cancer and eye damage. High in the atmosphere, about 25 kilometers (15 miles) above the Earth, ozone serves as a protective layer that absorbs harmful UV light.

Certain materials, such as those used in air conditioners, refrigerators and spray cans, can damage the ozone layer. Each fall, the results are visible over Antarctica, where an area of decreased ozone forms. Because this "ozone hole" has so little ozone, it allows lots of UV light to leak through.

Ozone hole
Image above: View of the South Pole from NASA's TOMS (Total Ozone Mapping Spectrometer) satellite. Blue and green indicate relatively large amounts of ozone. Red and yellow mark the "ozone hole," an area of decreased ozone. Credit: NASA
NASA is about to launch a new satellite into orbit around Earth to measure ozone. Called "Aura," the satellite will also measure many other gases, as well as smoke and dust in both the lower and upper atmosphere. It will also be able to measure and track chemicals that produce ozone.

World leaders have agreed to work together to limit the amount of ozone-depleting substances that enter the upper atmosphere. You can reduce the amount of ground-level ozone by walking, riding a bike, taking public transportation or carpooling. By lowering the number of automobiles on the road, we can decrease the amount of pollution in our air.

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Test Your Ozone IQ

Stephanie Stockman, NASA Goddard Space Flight Center
Adapted with permission from Celebrating Chemistry, a publication of the American Chemical Society, © Copyright 2003