Information about Ozone (O₃)

Current conditions

Sources
Health Effects
Air Quality Levels
Current EPA Air Quality Index and Clean Air Campaign Health Advisory

Sources

Ozone (O₃), a colorless gas, is the major constituent of smog. It is produced by the chemical reaction of nitrogen dioxide with reactive organic substances - such as hydrocarbons in automobile exhaust or vapors from cleaning solvents - in the presence of sunlight. This type of pollution first gained attention in the 1940's as Los Angeles "smog." Since then, photochemical smog has been observed frequently in many cities as well. (Note: In the upper atmosphere, naturally occurring ozone is beneficial in protecting us from the harmful solar rays.)
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Health effects

Ozone and other photochemical oxidants such as peroxyacyl nitrates and aldehydes are associated with health effects in humans. Peroxyacyl nitrates and aldehydes cause the irritation that is characteristic of photochemical pollution. Ozone has a greater impact on the respiratory system, where it irritates the mucous membranes of the nose, throat and airways; ninety percent of the ozone inhaled into the lungs is never exhaled. Symptoms associated with exposure include cough, chest pain, and throat irritation. Ozone can also increase susceptibility to respiratory infections. In addition, ozone impairs normal functioning of the lungs and reduces the ability to perform physical exercise. Recent studies also suggest that even at lower ozone concentrations some healthy individuals engaged in moderate exercise for 6 to 8 hours may experience symptoms. All of these effects are more severe in individuals with sensitive respiratory systems, and studies show that moderate levels may impair the ability of individuals with asthma or respiratory disease to engage in normal daily activities.

The potential chronic effects of repeated exposure to ozone are of even greater concern. Laboratory studies show that people exposed over a 6 to 8 hour period to relatively low ozone levels develop lung inflammation. Animal studies suggest that if exposures are repeated over a long period (e.g. months, years, lifetime), inflammation of this type may lead to permanent scarring of lung tissue, loss of lung function, and reduced lung elasticity.
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Air quality levels

In 1997, EPA revised the ozone standard for areas of the state which are outside the Atlanta non-attainment area. For these areas, the 1-hour ozone standard was replaced with an 8-hour average ozone standard. In 2008, EPA revised the 8-hour average ozone standard to lower the thresholds for ozone levels reported as 'Unhealthy' (see index below). Visit the EPA website to read more about EPA Regulatory Actions related to ground-level ozone.

The air quality standard for ozone, which is designed to protect public health with an adequate margin of safety, is 0.075* ppm, averaged over eight hours.
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Current EPA Air Quality Index and Clean Air Campaign Health Advisory

AQI Range	EPA Color Scale	EPA Descriptor	Clean Air Campaign Health Advisory
0 to 50	Green	Good	The air quality is good and you can engage in outdoor physical activity without health concerns.
51 to 100	Yellow	Moderate	At this level the air is probably safe for most people. However, some people are unusually sensitive and react to ozone in this range, especially at the higher levels (in the 80s and 90s). People with heart and lung diseases such as asthma, and children, are especially susceptible. People in these categories, or people who develop symptoms when they exercise at "yellow" ozone levels, should consider avoiding prolonged outdoor exertion during the late afternoon or early evening when the ozone is at its highest.
101 to 150	Orange	Unhealthy for Sensitive Groups	In this range the outdoor air is more likely to be unhealthy for more people. Children, people who are sensitive to ozone, and people with heart or lung disease should limit prolonged outdoor exertion during the afternoon or early evening when ozone levels are highest.
151 to 200	Red	Unhealthy	In this range even more people will be affected by ozone. Most people should restrict their outdoor exertion to morning or late evening hours when the ozone is low, to avoid high ozone exposures.
201 to 300	Purple	Very Unhealthy	Increasingly more people will be affected by ozone. Most people should restrict their outdoor exertion to morning or late evening hours when the ozone is low, to avoid high ozone exposures.
Over 300	Black	Hazardous	Everyone should avoid all outdoor exertion.

* EPA lowered the 8-hour average concentration standard from .08 ppm to .075 ppm, effective 03/12/2008.