Scientists report today in the New England Journal of Medicine that people who live in areas with high levels of ozone, a main constituent of smog, face a significantly higher risk of death from lung diseases than those living in areas with lower ozone concentrations. The study found the risk of dying from respiratory diseases to be 30 percent higher in metropolitan areas with the highest average smog levels.

The new study is the first to examine the long-term health impact of ozone exposure in metropolitan areas throughout the nation. Several studies have examined the effects of particulates, the small (less than 2.5 microns) particles present in soot, and found that exposure to these particles elevates the risk of heart and lung disease, but no previous study has examined the effects of long-term ozone exposure independent of particulates.

In the present study, researchers analyzed data on nearly half a million people who were living in 96 metropolitan areas of the U.S. between 1982 and 2000. They subtracted out the effects due to particulate pollution and found that while ozone does not increase the risk of cardiovascular disease like particulates do, ozone does severely impact respiratory health: the higher the ozone level in a particular city, the more likely its residents were to die of lung disease. For every increase of 10 parts-per-billion in ozone levels, the risk of respiratory death rose 4%. Even the city with the lowest ozone level, San Francisco, had an associated 14 percent increase in risk compared to no ozone exposure at all. The researchers controlled for individual risk factors, such as age, smoking status, body mass, and diet, and also for regional differences.

The present Environmental Protection Agency (EPA) air quality standards are based on short-term peaks in ozone exposure which occur during the spring and summer and can exacerbate existing respiratory conditions such as asthma and allergies. The present study links elevated risk of respiratory death to long-term cumulative effects of ozone exposure. The researchers note that their results suggest that environmental agencies should pay more attention to the health risks associated with long-term elevations in ozone levels. The EPA will be reviewing its ozone standard in the coming year.

Ground ozone (O₃), a reactive form of oxygen, is formed when sunlight reacts with nitrogen dioxide (NO₂), mostly from tailpipe and factory emissions) and oxygen (O₂) in the air. Its levels tend to be highest in the warmer months, in places with more overall sun exposure, and in cities with greater nitrogen dioxide emissions from cars and factories.

You can find out about current ozone levels in your area by visiting the government website http://airnow.gov/ . Want to learn more about respiratory diseases? Join the Healia Community for Lung Diseases. For more about allergies, read the Healia Health Guide to Outdoor Allergies or the Healia Health Guide on Allergies ; for more on asthma, see the Healia Health Guide to Asthma.

_{Photo: Dr. Keats, Flickr, Creative Commons}