What is ozone?

Dr. David Peden is director of the Center for Environmental Medicine, Asthma and Lung Biology at the UNC School of Medicine and deputy director of Child Health Research at the N.C. Translational and Clinical Sciences Institute. He explains the basics of ozone and what his research shows about the effects of ozone pollution on health. Questions and answers have been edited.

Q: This is the time of year when we see ozone alerts. What exactly is ozone?

Ozone is a form of oxygen in which three oxygen molecules interact with each other, as opposed to the gas we breathe, which is made up of two oxygen molecules. Because of its molecular structure, it is very easy for ozone to oxidize and to cause oxidative stress to a variety of things. Ozone could roughly be grouped with other oxidants like bleach and hydrogen peroxide.

Q: Is ozone always bad?

In the upper atmosphere it is actually a good thing, because it is one of the barriers that prevent too much ultraviolet light from making its way to the planet's surface, where it can cause melanoma and skin cancer. In the lower atmosphere, in the air that creatures breathe, ozone is not typically present unless there is a reaction between precursors of ozone such as volatile organic compounds and ultraviolet light. Then it is associated not just with respiratory issues but also with systemic issues like heart attack and stroke.

Q: Why do we have to worry about ozone in the summer?

It has to do with summertime weather patterns. When you see weather alerts about ozone that the weather service puts out, they are really looking for the likelihood of air being stagnant in an area for a while. When pollutants like nitric oxide and other organic compounds, which result from burning fossil fuels, are released into an atmosphere that is relatively stagnant, those compounds are trapped. That allows time for ultraviolet light to interact with those precursors in the atmosphere and result in ozone.

Q: What level of ozone is safe?

We and our EPA colleagues recently completed a study looking at the effects of 0.6parts per million of ozone on healthy volunteers. Our preliminary assessment suggests that even at that level of ozone, which is below the current standard of 0.8 parts per million, we can identify changes in lung function and airway inflammation. Where the rubber will meet the road is the administrator of the EPA will have to decide how big of a problem this is, how big of a public health threat this will be and whether the current ozone standard as outlined in the Clean Air Act will need to be changed.