Nature and Sources of the Pollutants

Ozone is a highly reactive gas that is a form of oxygen. It is the main component of the air pollution known as smog.

Ozone reacts chemically ("oxidizes") with internal body tissues that it comes in contact with, such as those in the lung. It also reacts with other materials such as rubber compounds, breaking them down.

Ozone is formed by the action of sunlight on carbon-based chemicals known as hydrocarbons, acting in combination with a group of air pollutants called oxides of nitrogen.

Hydrocarbons are emitted by motor vehicles, oil and chemical storage and handling facilities, and a variety of commercial and industrial sources such as gas stations, dry cleaners and degreasing operations.

Oxides of nitrogen are a by-product of burning fuel in sources such as power plants, steel mills and other heavy industry and in motor vehicles.

Ozone levels typically rise during the May through September period when higher temperatures and the increased amount of sunlight combine with the stagnant atmospheric conditions that are associated with ozone air pollution episodes.

The harmful ozone in the lower atmosphere (troposphere) should not be confused with the protective layer of ozone in the upper atmosphere (stratosphere) which screens out harmful ultraviolet rays.

Health Effects
Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. Symptoms include shortness of breath, chest pain when inhaling deeply, wheezing and coughing.

Research on the effects of prolonged exposures (6 1/2 hours) to relatively low levels of ozone have found reductions in lung function, biological evidence of inflammation of the lung lining and respiratory discomfort.

In studies of animals, ozone exposure has been found to increase susceptibility to bacterial pneumonia infection.

Recently, attention has begun to focus on the effects of long-term, repeated exposures to high levels of ozone. A study of a sample of long-time residents of Los Angeles, which has the highest and most frequent ozone problem in the nation, found that the group had a higher than expected loss of lung function over time. Long-term exposures of animals to moderate ozone levels produce changes in the structure of the lung.

Who is at Risk?
The U.S. Environmental Protection Agency (EPA) has identified three groups of people who are at particular risk from high ozone levels:

1. People With Pre-Existing Respiratory Disease

People with existing lung disease (e.g., chronic bronchitis, emphysema, asthma) already suffer from reduced lung function and therefore cannot tolerate an additional reduction in lung function due to ozone exposure.

2. A Sub-Group Of The General Public Referred To As "Responders"

Studies have found that a sub-group of the general healthy population responds to ozone exposure while exercising with significantly greater losses in lung function than the average response of the overall group under study. There is currently no way to identify these "responders" prior to ozone exposure, but the EPA estimates that this sub-group represents 5 to 20 percent of the total U.S. population.

3. Individuals Who Exercise Outdoors

Numerous laboratory and "real world" ozone exposure studies confirm that people who exercise, or otherwise participate in activities that increase their respiratory rate, respond much more severely to ozone exposure than people at rest.

What are the solutions?
The American Lung Association supports the use of stringent controls on motor vehicle and pollution emissions produced by the commercial and industrial sources of the hydrocarbon compounds and oxides of nitrogen that form ozone.

These controls include:

  • Strengthening pollution control requirements for new motor vehicles.
  • Improving the in-use performance of existing pollution control equipment.
  • Implementation of pollution controls to capture evaporating hydrocarbons in gasoline from motor vehicles and gas stations.

In addition, efforts to reduce our society's ever-increasing use of the automobile must be expanded, and controls on commercial operations and consumer products that contribute hydrocarbon compounds to the air will also be necessary.

National Ambient Air Quality Standards

The Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for the six major air pollutants considered harmful to public health and the environment. Localities where air pollution levels exceed the NAAQS are required to develop plans to reduce emissions.

In July 1997, the EPA strengthened the NAAQS for ozone from 0.12 parts per million averaged over 1 hour to 0.08 parts per million averaged over 8 hours. The agency is currently in the process of determining which localities exceed the standard.


This article was published by the American Lung Association.

Air Purifiers that Produce Ozone May Be Hurting Your Health
What is Ozone?
How Does "Bad" Ozone Affect Human Health and the Environment?
Ozone's Effects on Human Health
Production of harmful ozone plague ion-generating products sold as air cleaners
Ozone Generators that are Sold as Air Cleaners: An Assessment of Effectiveness and Health Consequences
Ozone: Nature and Sources of the Pollutants
Ozone Fact Sheet