Ozone: Good or Bad?

Ozone is a form of oxygen that can be necessary for health and environmental preservation. It is also a major component of urban smog, and can cause serious health problems and environmental degradation. Whether ozone is is blessing or a curse depends on whether it is part of the air we breathe or whether it protects us from exposure to excessive sunlight. Many of us who live in large cities are familiar with the fact that ozone is an air pollutant produced from some of the gases which escape into the air from the exhaust pipes of cars and other motor vehicles, so-called "ground-level" ozone. What some people may not know is that ozone also floats far above the earth where it forms a barrier against harmful solar energy. This barrier is known as "stratospheric" ozone," also called the "ozone layer."

What Causes Ground-Level Ozone

The most common source of ground-level ozone is the use of fossil fuels derived from oil--most gasoline and diesel fuel used today--to run cars, buses, trucks, trains, airplanes and other equipment powered by internal combustion engines. When the fuel is ignited by sparks to produce the explosions which ultimately turns the wheels, the leftover gases are dumped into the air through exhaust pipes intended for that purpose. Ozone is produced from some of these gases, called ozone "precursors."

The presence of sunlight makes the ozone situation worse by providing the light needed to complete the chemical reaction which produces ozone. Since summertime heat is caused by increased sunlight, summer is the season in which the most severe ozone pollution occurs.

Another factor which can affect the amount of ozone in the air we breathe is the shape of the earth's surface in areas that are otherwise prone to ozone pollution. For example, the Los Angeles metropolitan area is well-known for its extensive use of motor vehicles. It sits at the bottom of a basin formed by a low area surrounded by mountains. The mountains hold sunlight and motor vehicle exhaust in the basin for long periods of time, and this buildup results in the highest ozone concentrations of any urban area in the country.

How Ground-Level Ozone Affects Health

Many of us who have have spent time outside on smoggy days have experienced some of the short-lived impacts of ozone exposure including irritation of the eyes, nose and throat which often produces coughing, headaches and runny eyes and noses. Fortunately, these nuisances usually go away after we go indoors.

Long-term exposure is another story. Because ozone is a gas which we breathe, it produces negative effects on the respiratory system, primarily the lungs. Ozone attacks the cells which line the lungs, and can cause or aggravate existing cases of asthma, chronic obstructive pulmonary disease (COPD), emphysema and chronic bronchitis. Some of these conditions are incurable and can even result in death.

What Is Being Done About Ground-Level Ozone

For many years, the U.S. Environmental Protection Agency (EPA) and various state agencies have attempted to reduce the amount of ozone being produced in major metropolitan areas, where the problem is most severe due to the large number of motor vehicles being used there. For instance, the EPA has determined the maximum amount of ozone that can be present in the air without causing negative health effects. This is called the National Ambient Air Quality Standard for ozone, which EPA seeks to enforce in the areas where the amount of ozone has exceeded the standard. These areas include the country's largest cities such as Los Angeles, New York, and Chicago, as well as medium-sized cities such as Kansas City and St. Louis.

Many measures have been undertaken in pursuit of lower ozone levels. Most of us know about reducing motor vehicle emissions of ozone precursors through the use of emission control devices such as catalytic converters which are now required in the manufacture of many cars and trucks. In the urban areas where ozone pollution is most severe, other measure such as vehicle inspections, along with testing and frequent reporting of ozone concentrations are mandated by EPA, particularly in the summertime. The use of fuels which do not emit ozone precursors, such as ethanol and biodiesel, are being promoted. And research continues into other methods for powering vehicles, including electricity and hydrogen fuel cells.

Stratospheric Ozone

Unlike ground-level ozone, stratospheric ozone occurs naturally. It is found high above the earth, about six to thirty-one miles up in the stratosphereis, where it is not breathed by humans. This ozone layer protects all living things from excess ultraviolet (UV) radiation emitted by the sun. Too much of this energy can cause serious health problems and damage wildlife.

What Has Happened to the Ozone Layer

Signficant amounts of stratospheric ozone have been lost due to chemicals generated by human activity. These chemicals, primarily chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), have been used for many purposes. We are perhaps most familiar with their use as propellants in spray cans, as refrigerants in air conditioners and refrigerators and as a foaming agent in styrofoam production.

When CFSs and HCFCs became widely used, they were emitted in large amounts and moved by air currents up into the stratosphere. There, they entered into complicated chemical reactions which destroyed the ozone. This destruction of the ozone, called "ozone depletion," is more likely to happen in areas with extremely cold temperatures. However, ultimately it can happen above any other part of the earth if the CFC and HCFC concentrations are great enough. In fact, the entire globe has experienced a three percent average loss in the size of its ozone layer.

In the early 1980s, scientists first began to notice a thinning of the ozone layer over Antarctica where the depletion was causing the formation of a hole in the ozone layer. This hole eventually became larger and spread beyond the South Pole into other parts of the Southern Hemisphere, and even into the Northern Hemisphere. It was also observed that health problems caused or aggravated by UV radiation--premature skin aging and skin cancer, immune system depression, cataracts--were on the increase in the regions with the most ozone depletion. In some areas, such as Australia, local weather reports began to include information on what days and times people could expect high levels of UV exposure, so that they could take protective measures such as staying out of the sun.

What Is Being Done to Preserve and Protect the Ozone Layer

A few years later, concerns about ozone depletion reached a crisis point.. In 1987, the Montreal Protocol on Substances That Deplete the Ozone Layer was signed by the United States and several other countries. This treaty imposed bans and phaseouts of ozone-depleting chemicals being produced and used by humans. In order to comply with the treaty, the EPA has banned the use of many of these chemicals, and is phasing out the use of others. It is expected that these initiatives will prevent further ozone loss and eventually allow the ozone layer to recover, hopefully by the middle of this century.

Finally. . .

As both friend and foe, ozone continues to be a subject of government regulation, research and some controversy. Many of us have been personally affected by the results of ozone pollution and ozone depletion, and we will be asked to make changes in the future to assure that our environment and our health are maximazed by ozone reduction on the ground and by ozone recovery in the stratosphere.

Reference: www.epa.ozone