Ozone is a colorless gas composed of three atoms of oxygen. Ozone forms both in the Earth's upper atmosphere and at the surface. Where ozone forms determines whether it is helpful or harmful to your well-being.

Good ozone naturally forms in a layer about 10 - 30 miles (16 - 48 km) above Earth's surface. This protective layer shields us from the sun's harmful ultraviolet rays. Without this layer, we would all be blinded and sunburned. Unfortunately, human-created chemicals are destroying this beneficial layer of ozone. Over the South Pole in springtime, the ozone loss is so severe that an "Ozone Hole" forms, letting significant amounts of harmful ultraviolet light reach the surface. A smaller Ozone Hole sometimes occurs over the northern polar regions.

Bad ozone forms near Earth's surface when the ultraviolet light in sunlight triggers a chemical reaction with "precursor pollutants" emitted by cars, power plants, and industrial sources. These precursor pollutants consist of nitrogen oxides (NOx) and volatile organic hydrocarbons (VOC). Ozone near ground level is a harmful pollutant. Ozone levels are carefully monitored during the summer months when the weather conditions are perfect for it to form. Sunshine, hot temperatures, and high emissions of NOx and VOC pollutants lead to high levels of ozone.

An Ozone Action Day is declared when weather conditions are likely to combine with pollution emissions to form high concentrations of ground-level ozone that may cause harmful health effects. People and businesses should take action to reduce emissions of ozone-causing pollutants.

The Environmental Protection Agency uses its Air Quality Index to provide general information to the public about air quality and associated health effects. An Air Quality Index (AQI) of 100 for any pollutant corresponds to the level needed to violate the federal health standard for that pollutant. For ozone, an AQI of 100 corresponds to 0.08 parts per million (ppm) over an 8-hour period -- the current federal standard. Over half of the U.S. population lives in areas where the AQI exceeds 100 and violates the federal health standard at least once per year. Some metropolitan cities have severe air pollution problems, and can see ozone AQI values in the 200s or even 300s.

In 1997, the Environmental Protection Agency (EPA) proposed a new standard for ozone and particulate matter levels in the atmosphere. The ozone levels were not to exceed 0.080 ppm during an 8-hour period. However, a coalition of business and industry interests sued to have those standards blocked, claiming they were too expensive and ill-conceived. In 1999 a federal court agreed, issuing a ruling blocking implementation of the tougher standards.

Changes were made again in February 2001, when the U.S. Supreme Court unanimously upheld the constitutionality of the Clean Air Act as EPA had interpreted it in setting health-protective air quality standards for ground-level ozone and particles. The Supreme Court also reaffirmed EPA's long-standing interpretation that it must set these standards based solely on public health considerations without consideration of costs.

However, the Supreme Court did find that the EPA's plans for implementing the rules were unreasonable, and it ordered the agency to develop new implementation policies. Industry opponents immediately promised to use this aspect of the ruling as the basis for new legal challenges to weaken implementation of the new standards. It remains to be seen if the new standards will truly take effect as legislated.

According to the EPA, the new ozone and particulate matter standards will have the following effects:

Reduced risk of significant decreases in children's lung functions. The new standards should provide approximately 1 million fewer incidences of difficulty of breathing or shortness of breath in children each year. These problems can limit a healthy child's activities or result in increased medication use, or medical treatment, for children with asthma.

Reduced risk of moderate to severe respiratory symptoms in children. The new standards should result in hundreds of thousands of fewer incidences each year of symptoms such as aggravated coughing and difficult or painful breathing.

Reduced risk of hospital admissions and emergency room visits for respiratory causes. The new standards should result in thousands fewer admissions and visits for individuals with asthma.

Reduced risks of more frequent childhood illnesses and more subtle effects such as repeated inflammation of the lung, impairment of the lung's natural defense mechanisms, increased susceptibility to respiratory infection, and irreversible changes in lung structure. Such risks can lead to chronic respiratory illnesses such emphysema and chronic bronchitis later in life and/or premature aging of the lungs.

Reduced yield losses of major agricultural crops, such as soybeans and wheat, and commercial forests by almost $500,000,000.

Death rates due to lung and heart problems increase by a .64% soon after ozone levels peak, according to several publications by Michelle Bell, an air-quality and health expert at Yale University. Bell showed that an ozone increase of 10 parts per billion (ppb), even at levels less than the 80 ppb federal standard, triggered the higher death rates. If ozone levels dropped by 10 ppb, almost 4,000 lives could be saved each year in the 95 cities she studied.

High ozone levels have been linked to increases in the severity of asthma attacks and other respiratory health problems, especially for children and the elderly. About 7 percent of healthy people have shortness of breath with ozone levels at 60 parts per billion (ppb), so the EPA is considering tightening the ozone standard from the current 80 ppb down to 60 ppb.

Even healthy people will experience irritation of the respiratory system. Ozone causes constriction of the bronchial airways such as coughing, sore throat, ear aches, wheezing, chest discomfort, uncomfortable breathing. People who exercise or work outdoors may experience reduced exercise capacity. Those individuals with heart and lung disease react more severely to air pollution. People with asthma have more asthma attacks when ozone levels are high. Ozone makes individuals become more sensitive to allergens and can also be involved in the development of asthma. Ozone weakens the immune system and facilitates the development of lung infections. Thus ozone can inflame and damage the lung tissue.

Children are most at risk from exposure to ozone:
The average adult breathes 13,000 liters of air per day. Children breathe even more air per pound of body weight than adults. Because children's respiratory systems are still developing, they are more susceptible than adults to environmental threats. Ground-level ozone is a summertime problem, and children are at risk when they are outside playing and exercising during the summer months at summer camps, playgrounds, neighborhood parks and in backyards.

Asthmatics and Asthmatic Children:
Asthma is a growing threat to children and adults. Children make up 25 percent of the population and comprise 40 percent of the asthma cases. Fourteen Americans die every day from asthma, a rate three times greater than just 20 years ago. African-Americans die at a rate six times that of Caucasians. For asthmatics having an attack, the pathways of the lungs become so narrow that breathing becomes akin to sucking a thick milk shake through a straw. Ozone can aggravate asthma, causing more asthma attacks, increased use of medication, more medical treatment and more visits to hospital emergency clinics.

Healthy Adults:
Even moderately exercising healthy adults can experience 15 to over 20 percent reductions in lung function from exposure to high levels of ozone over several hours. Damage to lung tissue may be caused by repeated exposures to ozone -- something like repeated sunburns of the lungs -- and this could result in a reduced quality of life as people age. Results of animal studies indicate that repeated exposure to high levels of ozone for several months or more can produce permanent structural damage in the lungs. Among those most at risk to ozone are people who are outdoors and moderately exercising during the summer months. This includes construction workers and other outdoor workers.

Recommended links:
EPA website on ozone pollution.
American Lung Association website on ozone pollution.

For detailed information about real-time pollution levels in the U.S., visit the Environmental Protection Agency's Website.