Department of Health and Human Services
The Basics
What is ozone?
Ozone is a gas made up of three atoms of oxygen. You can't see it and, in low concentrations, you can't smell it. It is found in both the upper atmosphere and at ground level.
You might be confused when you hear that ozone can be bad, because you've probably heard a great deal about the importance of the "ozone layer" and how it protects us from the sun's harmful ultraviolet rays. This atmospheric ozone -- found 10 to 30 miles above the Earth's surface -- is good.
But, ozone at ground level is bad. Ozone is a reactive chemical. It has three oxygen atoms and that third oxygen atom is always ready to "react" with something. When that something is your airways, lungs, or eyes, it can hurt you.
How is ground level ozone created?
Three things are necessary to create ground level ozone --- volatile organic compounds (VOCs), oxides of nitrogen (NOx) and sunlight. Cars, power plants, industrial boilers, refineries, chemical plants and other sources emit VOC and NOx. Sunlight "cooks" VOC and NOx, creating ground level ozone.
- Ozone Home Page
- The Basics
- The Symptoms
- Protecting Yourself
- Indoor Ozone
- If You're Serious about Ozone
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Page last updated on Friday February 10 2012