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What is Ozone?
Ozone (O3) is a highly reactive form of oxygen. At normal concentrations it is
colorless and odorless. At high concentrations (often associated with
thunderstorms or arching electric motors) it is an unstable bluish gas with a
pungent odor. Ozone is a major component of photochemical smog. Yet, the
visibility reduction and odor resulting from smog are produced by other
pollutants such as particulates and nitrogen oxides. Ground level ozone in high
concentrations is considered an air pollutant, while stratospheric ozone in the
upper atmosphere (12 - 30 miles above the ground) is critical for absorbing
cancer-causing ultraviolet radiation.
Where does ozone come from?
Ozone is a secondary pollutant formed when nitrogen oxides and hydrocarbons
react in the presence of sunlight. Hyrdocarbons come from automobile exhaust
(and also some vegetation) and nitrogen oxides come from burning fuel.
How does ozone affect human health?
The reactivity of ozone causes health problems because it damages lung tissue,
reduces lung function, and increases the sensitivity of the lungs to other
irritants. Symptoms of decreased lung function include chest pain, coughing,
sneezing and pulmonary congestion. Ozone can also act as an irritant to the
mucous membranes of the eyes and throat and can reduce immune system capacity.
In high concentrations, ozone causes damage to plants and deteriorates materials
such as rubber and nylon.
Who is most at risk?
Scientific evidence suggests that ozone affects not only individuals with
respiratory problems, but also affects healthy adults and children.
What are the EPA standards for ozone?
In July 1997, the EPA approved a revision to the ozone standard. Previously, the
primary National Ambient Air Quality Standard (NAAQS) for ozone was 0.12 ppm
(parts per million), averaged over a one hour period. The new standard is 0.08
ppm, averaged over an 8 hour period, based on the three-year average of the
fourth highest daily concentration. For more information on the new standards,
see the US EPA Office of Air Quality Planning and Standards Web site.
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