Updated: Sep 14, 2022
When you hear the word “ozone” do you automatically think of the kind way up in the Earth’s stratosphere? If so, did you know that’s the good kind of ozone? Naturally occurring, atmospheric ozone creates a protective layer that helps shield us from ultraviolet rays.
Ground-level ozone, on the other hand? It’s the damaging kind.
Why? At ground level, ozone is a harmful type of air pollution that is classified as a criteria pollutant by the U.S. Environmental Protection Agency because its level in outdoor air needs to be limited based on health criteria. Heard of the term smog? Ozone is its main ingredient.
For those who might not be familiar: Ground-level ozone is created by chemical reactions occurring between nitrogen oxides (Nox) and volatile organic compounds (otherwise known as VOCs). This happens when sunlight chemically reacts with pollutants emitted by:
And even some species of trees
Ozone is most prevalent – and most likely to reach unhealthy levels – during the warm-weather months and in urban environments. And while it may be initially created in an urban area, ozone can travel long distances and accumulate to high concentrations far away from the original sources.
Starting 2016, the ozone season for Allegheny County extends from March 1 through Oct. 31.
In the most recent American Lung Association State of the Air report, Allegheny County received an F grade for the number of days with high levels of ozone. So, clearly we’ve got work to do to reduce sources of NOx and VOCs contributing to our region’s formation of ground-level ozone.
Ground-level ozone takes a human toll: Inhaling ozone can cause everything from throat irritation and coughing to chest pain and airway inflammation that makes it difficult to breathe. Ozone can even reduce lung function and harm lung tissue, and exposure can exacerbate conditions like asthma and other breathing issues. Some scientists have compared ozone-caused lung damage to a sunburn.
People most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers. In addition, people with certain genetic characteristics, and people with reduced intake of certain nutrients, such as vitamins C and E, are at greater risk from ozone exposure.
During the growing season, ozone also impacts myriad plants. You can learn more about those by watching this video put together by our Education and Events Coordinator Chelsea Hilty.