Ozone
Ozone is unstable and irritating
Ozone is a special form of oxygen. Like ordinary oxygen, ozone is one of the many gases in the air we breathe. Like oxygen, ozone is made up of oxygen molecules. But, while the molecules of ordinary oxygen are made up of two chemically linked oxygen atoms, the molecules of ozone are made of three such atoms. With its third atom of oxygen, ozone is not very stable-that is, it ordinarily doesn't last very long.
A little ozone occurs naturally. An energy source such as lightning can produce it - temporarily breaking up pairs of oxygen atoms and reforming them as chemically linked clusters of three oxygen atoms: ozone. People, other animals and plants tolerate such naturally occurring, short-lived ozone pretty well. But when ozone builds up-generally as a result of our use of fossil fuels-it reacts very strongly with animal and plant tissues, and even damages tough materials such as rubber, plastics and outdoor paints.
You've probably seen hydrogen peroxide fizz-and perhaps felt it burn your gums or skin tissues, or "smart." Like ozone, hydrogen peroxide is closely related to a very stable molecule: water, or H2O. With an added oxygen atom, it changes to H2O2, becoming very reactive.
The fizz and burn of hydrogen peroxide on a scratch or wound illustrate how, at high concentrations, ozone's own strong reactivity can irritate and damage the sensitive tissues of your eyes, lungs, nose, sinuses and throat, causing burning eyes, shortness of breath, chest tightness, wheezing, coughing and nausea. The sustained, higher levels of ozone that cause these effects usually begin with human activity.
That is, when we use electricity for our lights, computer and TV, when we heat our houses and run our cars and SUVs, or even when we roast chestnuts on an open fire or charcoal a steak, these activities often require the burning of fossil fuels-hydrocarbons such as gasoline, heating oil, firewood, charcoal and the coal for power plants. This combustion releases oxides of nitrogen, which are gaseous combinations of oxygen and nitrogen, nitrogen being another common gas in our atmosphere. One of these combinations is nitrogen dioxide (NO2). When NO2 absorbs energy from sunlight, it breaks down to nitric oxide (NO) and a free oxygen atom.
The free oxygen atom then barges into the oxygen pair to form the linked triplet of ozone (O3).
When ozone accumulates, it hurts people, pets, crops
Normally, ozone converts back to oxygen. However, airborne hydrocarbons (from motor vehicles, industrial emissions and other kinds of incomplete combustion and solvent use) can disrupt this conversion, allowing the ozone to accumulate. Because sunlight and heat play roles in the smog process, ozone concentrations most often rise in the warmer months of the year and peak in the warmer hours of the day.
While winds might dissipate the ozone, temperature inversions frequently occurring during warm weather over many cities can hold down and stagnate the lower atmosphere, allowing ozone to build up. And there you have it: grey, thick, photochemical smog-- urban smog.
Thus, the centers of ozone pollution are the great centers and suburbs of humankind's activity: Los Angeles, Houston, Atlanta, New York, Boston and other large metropolitan areas. (That's why in some cities in developing countries, people are somewhat proud of smog-as a sign of industrialization's progress.)
An Inversion - You hear about it on a TV weather a lot: Normally, Warm air rises until it cools at higher altitudes, thus moving and mixing the air. A temperature inversion occurs when the upper air is warmer and prevents the lower air from rising, trapping it in place.
| In rural areas, less ozone is likely to accumulate. There are fewer gasoline automobiles, homes and factories. In addition, moisture in rural soil and trees absorbs some of the radiant energy from the sun, keeping these areas cooler than nearby cities. But rural areas do not escape the effects of ozone entirely. Trees themselves generate some hydrocarbons and add to ozone levels. Many power plants that burn fossil fuels are in rural areas, increasing the concentrations of oxides of nitrogen in rural air. According to "the weatherman," the National Oceanic and Atmospheric Administration, rural sections of the East and South have among the highest summer ozone readings in North America partly as a result of spillover from cities and suburbs. |  |
HOW OZONE DISTURBS YOUR BODY - Inhaled ozone travels down the windpipe and enters the lungs through the large bronchial tubes, which branch into smaller airways, or bronchioles. At the end of the bronchioles are tiny air sacs called alveoli, which fill up and expand like little balloons to put oxygen into the bloodstream. Ozone primarily injures these key oxygen exchangers, the alveoli, along with the bronchioles. Animals also suffer from ozone. Studies demonstrate how ozone exposure injures their lung cells and causes unusual changes in lung tissue. Other studies have shown that ozone can make people more susceptible to bacterial pneumonia, a potential killer.
Tests show lost lung capacity, poorer athletic performance
A third group that may be particularly susceptible to ozone is made up-ironically-of healthy, not-particularly-sensitive people who exercise a lot outdoors. Studies show that adults exercising vigorously react more to ozone exposure than do adults at rest. People working or exercising increase their breathing rate, so that they inhale more ozone and thus a higher dose reaches the target tissues of the bronchioles and alveoli.
- Ozone affects a person's vital lung capacity-the volume of air that can be expelled from fully inflated lungs. In controlled tests, a 5 to 10 percent reduction occurred in volunteers engaged in moderate exercise for 6.5 hours at just 80 ppb. In the "real world," active kids at camp showed reduced vital lung function when ozone was higher than normal.
- Athletic ability, as measured by performance on stationary bikes or treadmills, has been shown to be poorer at 180 ppb than among controls performing in normal air.
- Ozone concentrations can make the small bands of muscles that help control breathing more sensitive to dry air, cold or dust, so they contract, narrowing the airways and making breathing more difficult.
- In five cities studied by researchers in Massachusetts, hospital admissions for pneumonia and flu were highest in the cities with higher maximum ozone levels and particulate levels.
Ozone is so reactive, so irritating, you might wonder if it causes cancer. There's some generally good news on that score: The National Toxicology Program, headquartered at NIEHS, found that rats exposed to ozone for from two years to 30 months did not have a significant increase in tumors-nor did ozone add to the risk of rats exposed to a known carcinogen in tobacco smoke. Only at the high exposure of 1 part per million did a marginal increase in lung tumors appear, and that could be coincidental.
OZONE HAS PROVED HARD TO REDUCE
Some emissions have been greatly reduced under the Clean Air Act of 1970 (with amendments in 1977 and 1990). Today's air is noticeably cleaner than a few decades ago. But ozone, which results from a reaction between emissions and other substances, has proved harder to reduce. A report of the National Academy of Sciences a few years ago put it pretty bluntly: State and federal restrictions, along with industry practices, had "largely failed" to decrease ozone exposures. As the century ended there were still 32 "nonattainment" areas containing 40 cities in which people are exposed to ozone in excess of the air-quality standards set to protect people's health. A nonattainment area may involve three urban, highly populated states, such as New York, New Jersey and Connecticut, so many people are exposed to unacceptably high levels of ozone.
Ultraviolet (UV) Alerts
To help avoid painful sunburn and blisters and such long-term problems as skin cancer and sight-dulling cataracts, many weather reports now include information on the UV Index. Using two National Oceanic and Atmospheric Administration-operated satellites, the National Weather Service and the Environmental Protection Agency forecast the UV risk (or Index Value) based in part on the wavelengths of the UV radiation (some being more harmful than others) and on whether clear skies or cloudy are expected.
To reduce the risk of cataracts and other eye damage, sunglasses are advised for UV values of 5 (moderate) or higher. Good sunglasses are also advised at the beach, on the water, or on snow, at all times, even when the index is minimal.
Informations obtained from National Institute of Health.