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.

How does ozone affect my health?
There is lots of good, scientific research concerning the effect of ozone on people. Ozone can affect your lungs and respiratory system in several ways.

Ozone can irritate your respiratory system. This might come in the form of coughing or an uncomfortable feeling in your chest. Symptoms may last a few hours after exposure.
Ozone can impair your ability to breathe. You may not be able to breathe in as much as air as you are normally able to. Your breathing might be more rapid and shallow.

Ozone can aggravate asthma. Doctors report that high ozone levels result in a greater number of asthma attacks. That's because asthmatics are more greatly affected by the irritant. Ozone also makes you more sensitive to allergens that cause asthma attacks. Ozone can also aggravate chronic lung diseases like emphysema and bronchitis.

Ozone can inflame and damage the lining of your lungs. Ozone can damage the cells that line your lungs. Eventually, these damaged cells are replaced. But, repeated damage may result in permanent problems.

These are all short-term health effects. Scientists are researching ozone's long-term effects. There is a concern that the developing lungs of children repeatedly exposed to high levels of ozone may be damaged. Some studies in animals suggest that ozone may also harm the ability to fight off respiratory infections.

Who is most likely to be harmed by ozone?
Children, adults who are active outdoors, and people with respiratory diseases are most likely to be harmed by high levels of ozone. Some people who don't fall into any of these categories are apparently more sensitive to ozone and also suffer problems.

What are the symptoms of ozone exposure?
You may cough or have impaired or painful breathing. People with emphysema or bronchitis may see a worsening of symptoms.

Are there always symptoms from exposure to ozone?
No. Ozone damage can occur without any noticeable signs. People who live in areas where ozone levels are frequently high may find that their initial symptoms go away over time, particularly when exposure to high ozone levels continues for several days. Ozone continues to cause lung damage even when the symptoms have disappeared. The best way to protect your health is to find out when ozone levels are elevated in your area and take simple precautions to minimize exposure even when you do not feel obvious symptoms.