Science Says: Two Hours of Ozone Exposure Could Cause Heart Attacks

Citizens in large urban areas, like Los Angeles and Houston, are particularly at risk.
Anyone down for a nice day outside in Los Angeles? (Photo: Getty Images)
Jun 27, 2012· 1 MIN READ
The director of the Public Trust Project, Alison Fairbrother has written for Grist and Politics Daily, among others.

This just in: smog is bad for your heart. Really, really bad.

A group of healthy young volunteers exposed to just two hours of ozone, a primary component of smog, suffered vascular inflammation and changes in heart rhythm, symptoms that cardiologists associate with heart attack and sudden death.

While these changes were reversible in the healthy young participants, researchers say the results raise concerns about the elderly and people with existing heart conditions.

The study, published this week in Circulation, an American Heart Association journal, provides a “plausible explanation of the link between acute ozone exposure and death,” the study’s leader author Robert B. Devlin, Ph.D., a senior scientist at the U.S. Environmental Protection Agency’s National Health and Environmental Effects Research Laboratory, said in a news release. The study was funded by the Environmental Protection Agency (EPA).

Ground-level ozone (not to be confused with the ozone layer in the atmosphere that protects the Earth from harmful UV rays), is created when pollutants from vehicles, power plants, and industrial processes react to sunlight.

A common air pollutant, ozone can trigger a variety of health problems, including worsening bronchitis, emphysema, and asthma, as well as reducing lung function, according to the EPA.

It is a particular problem during summer months, when strong sunlight mixes with pollutants to produce harmful concentrations of ozone in the air we breathe. Under the Clean Air Act, the EPA has mandated that exposure to ozone should not exceed .076 parts per million (ppm) over the course of an eight-hour period.

In the Circulation study, EPA researchers focused on short-term effects of ozone-polluted air, exposing 23 young participants, ages 19 to 33, to .3 parts per million (ppm) of ozone, higher than EPA’s standard. Volunteers alternatingly cycled on a stationary bike and rest in 15-minute spurts.

While none of the participants complained of physical symptoms, tests showed that the ozone exposures had changed their bodies’ natural ability to dissolve clots that form on arterial walls, increased blood levels of inflammatory agents, and caused changes in heart rate.

These results are particularly relevant to U.S. residents living in highly polluted regions.

Los Angeles, for example, has the highest levels of ozone nationwide, with nine total cities in California ranking as top ozone polluters. Houston, Texas is also on the list.

According to the American Lung Association’s State of the Air report, 41 percent of Americans live in counties that have unhealthy levels of ozone or particle pollution. The World Health Organization estimates that 2 million people worldwide die because of acute exposure to air pollution.

As the scientific evidence showing the health risks of pollution builds, concerned citizens should take steps to limit ozone exposure:

At, you can find daily air quality reports for many areas of the country that are at increased risk for high levels of ground ozone. is a service that sends email alerts when air pollution in your area reaches dangerous levels.

Read more about actions you can take to limit your time in ozone-polluted air here.

Would you ever consider moving from a city because its air was too polluted?