Ozone (O3) is a very "active" form of oxygen which
reacts rapidly and strongly with living tissues, plant-derived fabrics, dyes,
rubber and many other man-made materials. A colorless gas, it has no odor except
near high energy sources such as strong electrical arcs, sparks or close to a
lightning strike. Ozone is the major photochemical oxidant and represents about
90% of all oxidants found in the air.
Ozone forms as a secondary pollutant, which means it is not directly emitted
but is produced by a reaction involving other substances in the air.
Hydrocarbons (volatile organic compounds, or VOC's) and nitrogen oxides (NOx),
the ozone precursors, chemically react in sunlight to form ozone.
Sources of VOC's include:
- Automobile exhaust.
- Gasoline and oil storage and transfer.
- Industrial use of paint solvents, degreasing agents, cleaning fluids, and
- Incompletely burned coal or wood.
Plants, to a lesser degree, give off similar substances, such as terpenes
from pine trees.
Ozone derived from these sources and present near the earth's surface
("ground-level ozone") should not be confused with the stratospheric
ozone layer located about fifteen miles above the earth. The stratospheric ozone
layer helps shield the earth from cancer-causing ultraviolet rays.
The highest ozone levels in New Mexico occur from mid-May to mid-September,
especially in hot weather with light winds. Depending on the weather, ozone can
remain in an area several days, with the highest levels building up in the
afternoon and continuing into the evening.
Ozone is a highly reactive gas that affects the respiratory system by
severely irritating the mucous membranes of the nose and throat. Since 90% of
the ozone breathed into the lungs is never exhaled, ozone molecules react with
sensitive lung tissue to cause several health consequences. Ozone's effects are
more severe in individuals with preexisting respiratory disease. The length and
frequency of exposure, as well as concentration, are significant factors in
determining the many effects, which may include the following:
- Increased susceptibility to respiratory infection.
- Impaired lung function and reduced ability to perform physical exercise.
(Recent studies suggest that healthy exercising individuals exposed to 120
parts per billion (ppb) of ozone for one hour experience significant
shortness of breath. Similar decreases are also seen upon a 6 hour exposure
to 80 ppb.)
- Severe lung swelling and death, due to short-term exposures greater than
- Increased hospital admissions and emergency room visits for respiratory
diseases, which may be associated with exposures to one-hour ozone
concentrations greater than 120 ppb.
Activity levels (e.g. moderate-heavy exercise) and environmental stress (e.g.
humidity and high temperatures) also affect susceptibility. Other factors
- Individual sensitivity.
- Age (children and young adults appear to be more sensitive than older
- Smoking status (smokers appear to be less sensitive than non-smokers).
- Chronic obstructive pulmonary disease or asthma, which may increase
susceptibility to ozone-induced decreases in lung function. (Decreases in
lung function are greater in asthmatics concurrently exposed to ozone and
pollen than for either pollutant alone.)
- Possibly additive or synergistic effects when ozone combines with sulfur
dioxide, nitrogen dioxide, carbon monoxide, sulfuric acid, or other
Effects of chronic ozone exposure are not as well characterized.
Epidemiologic studies suggest lung function generally decreases in people living
in areas with high ozone levels. Animal studies indicate chronic ozone exposure
may contribute to the development of chronic lung diseases and bacterial
infections and may accelerate lung aging.
Ozone causes noticeable leaf damage in many crop and tree species. Research
indicates this damage occurs at concentrations commonly monitored during the
warm months (i.e. 60 ppb to 120 ppb). Certain varieties of soybeans, clover,
onions, spinach, muskmelon and alfalfa are especially susceptible. (Nation-wide,
ozone is responsible for agricultural crop yield losses of several billion
Ozone can also weaken materials such as rubber and fabrics.