Ozone (O3) is a gas emitted into the air and is created at ground level by a chemical reaction between nitrogen oxides and volatile
organic compounds in the presence of heat and sunlight. Motor vehicle exhaust, emissions from industrial plants, chemical
solvents and gasoline vapors are the chief sources that produce ozone. Ground-level ozone and ozone occurring in the atmosphere
have the same chemical composition. Ozone that forms 10-30 miles above the earth's surface forms a protective layer to block
the sun's harmful rays. This is considered good ozone while the same compound formed at ground level can irritate lung tissue
and cause inflammation. Even low levels can cause aggravated asthma, reduced lung capacity and decrease exercise tolerance
and increased susceptibility to infection. Repeated exposure can cause scaring of the lung tissue leading to permanent damage.
This is considered bad ozone. Because ozone formation requires heat and sunlight, it is known as summertime irritant and commonly
is found in high levels in urban areas. But ozone carries well in wind, and rural areas many hundreds of miles removed from
the initial site of formation can be affected seriously.
Particulate matter (PM) is the term used for particles found in the air. These particles can be large enough and dark enough
to be seen—as in dust, dirt, soot and smoke—or they can be so small that they can be detected only by electron microscope.
Some particles come from engines emissions, factories, dust and dirt from construction sites, tilled fields, horse arenas,
unpaved roads and from burning wood. Others come from chemical reactions from fuel combustion. These particles also can damage
lung tissue and initiate inflammatory responses in sensitive individuals at even low levels. PM also is likely to cause significant
throat irritation resulting in coughing, and it is the major cause for eye irritation and excessive ocular discharge, redness
Carbon monoxide (CO) is primarily the result of burning vehicle fuels and, as such, is produced in large quantities in urban
areas. CO causes intense irritation to lung tissue and can be lethal in high concentrations. Nitrogen dioxide (NO2) occurs when fuel is burned at high temperatures and is mainly produced by vehicles, electric utilities, and industrial combustion
processes. Sulfur dioxide (SO2) is produced mainly by coal-burning electric utilities at a rate of nearly 13 million tons per year. In the air, the SO2 reacts with other chemicals to form small sulfur particles that gather in the lungs and cause tissue damage.