Ozone

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.

Sources

Ozone forms as a secondary pollutant, which means it is not directly emitted into the air but is produced by a chemical reaction between nitrogen oxides and volatile organic compounds in the presence of sunlight..

Sources of VOC's include:

  • Automobile exhaust.
  • Gasoline and oil storage and transfer.
  • Industrial use of paint solvents, degreasing agents, cleaning fluids, and ink solvents.
  • Incompletely burned coal or wood.

Plants, to a lesser degree, give off similar substances, such as terpenes from pine trees.

Ozone pollution from these sources is present near the earth's surface ("ground-level ozone"). It has the same chemical structure as the stratospheric ozone layer located about fifteen miles above the earth. However, ozone can be "good" or "bad" depending on its location in the atmosphere. "Good" ozone occurs naturally in the stratosphere and forms a layer that shields and protects life on earth from cancer-causing ultraviolet rays. In the earth's lower atmosphere, ground-level ozone is considered "bad."

Here in Southwestern Ohio, the highest ozone levels occur from April 1 to October 31, especially in hot hazy weather with southerly 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. The length of the ozone season varies from one area to the next depending upon the climate. Southern states may have an ozone season that lasts nearly the entire year.

It was once believed that unhealthy levels of ozone (and its precursors) were confined to urban areas. However, ozone levels exceeding national health standards are measured in more rural areas as well. These rural concentrations may result from the transport of ozone and its precursors over long distances by the wind, indicating the regional (rather than local) nature of this air pollution problem.

Health Effects

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.
  • Aggravates asthma.
  • 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 300 ppb.
  • 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 include:

  • Individual sensitivity.
  • Age (children and young adults appear to be more sensitive than older adults).
  • 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 particulate aerosols.

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.

Other photochemical oxidants, for example peroxyacetyl nitrate, may make eyes water. Some may have bad odors, like those in Los Angeles-type smog. Very few of these other types of oxidants are present in Wisconsin's ambient air.

Other Effects

Ozone interferes with plant's ability to produce and store food, making them more susceptible to disease, insects, other pollutants, and harsh weather. 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 dollars.) Trees, such as lilac, aspen and ash are also sensitive.

Ozone can also weaken materials such as rubber and fabrics