Smarter Living: Chemical Index

Ozone is the main component of smog. Spikes in ozone pollution have been linked to thousands of premature deaths each year.

Health Concerns

In the stratosphere, a layer of ozone protects the Earth from harmful ultraviolet rays. But closer to the ground, ozone is a pollutant that causes throat irritation, chest pain, wheezing, coughing and breathing difficulties, particularly for children and people with asthma or other respiratory illnesses. Spikes in ozone pollution have been linked to increases in emergency room and hospital visits, and thousands of premature deaths in urban areas each year.


Ozone is formed when pollutants from tailpipe exhaust, power plants, gas stations, chemical plants and other sources combine in the presence of heat and sunlight. Hot summer days tend to create more ozone, and more health problems for people who work or play outside.

Global warming is expected to increase the number of bad air days in the eastern and southern United States. Urban areas tend to have more bad air days, but suburban and rural areas can be hit with ozone pollution as well, as winds carry emissions far from their original source.

Stay Safe

Freeways, railyards, freight terminals and big industrial facilities are major sources of ozone pollution. If you can, maintain a distance of at least 1,000 feet between these pollution sources and your home, work and recreational space. This is especially important if you have a child with asthma.

Check the air quality forecast in your area and stay indoors as much as possible on bad air days.

Do your most strenuous outdoor activities on days with relatively low ozone levels, or in the morning before ozone levels rise.

Take Action

Everyone has a right to breathe clean air. That's why Congress passed the Clean Air Act in 1970 and created the EPA to carry it out. The EPA set a limit on how much ozone can be in the air, but according to its own scientific advisors, that limit is too high to protect public health.

Studies have shown that even healthy people can have trouble breathing air that meets the EPA’s ozone standard.  Strengthening the standard would save thousands of lives. And reducing emissions from cars, power plants and other sources of smog-forming pollutants would help clear the air for millions of Americans.

Learn More

Ground level ozone. U.S. EPA.

NRDC Report: Heat Advisory

NRDC Switchboard: latest blog posts on smog

Bell, M. L., R. Goldberg, C. Hogrefe, P.L. Kinney, K. Knowlton, B. Lynn, J. Rosenthal, C. Rosenzweig, J. A. Patz, 2007. Climate change, ambient ozone, and health in 50 US cities. Climatic Change 82:61-76.

last revised 12/27/2011

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