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Ground-Level Ozone and Your Health

Ozone is an extremely reactive gas comprised of three atoms of oxygen. Ozone exists naturally in the earth's upper atmosphere, the stratosphere, where it shields the earth from the sun's harmful ultraviolet rays. However, ozone found close to the earth's surface, called ground-level ozone, is a component of smog and a harmful pollutant.

What is ground-level ozone? Where does it come from?

Ground-level ozone is a colorless gas that can be found in the air we breathe. It is formed through a complex chemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. Sources of manmade VOCs and NOx include: 1) automobiles, trucks and buses; 2) gasoline storage and transfer; 3) large combustion and industry sources such as utilities; 4) industrial use of solvents and degreasing agents; 5) consumer products such as paints and cleaners; and 6) off-road engines such as aircraft, locomotives, boats, construction equipment and lawn and garden equipment. VOC's are also produced naturally by certain types of vegetation.

Who is considered most at risk from exposure to ground-level ozone?

  • Children are the most at risk from exposure to ground-level ozone: their respiratory systems are still developing and they breathe more air per pound of body weight than adults. Ground-level ozone is a summer time problem; children spend most of the summer outside playing at summer camps, playgrounds, neighborhood parks and in backyards.
  • Individuals suffering with a respiratory disease are also at risk because exposure to ground-level ozone inhibits the lungs' ability to function properly. People with existing lung disease (e.g., asthma, chronic bronchitis, emphysema) already suffer from reduced lung function and, therefore, cannot tolerate an additional reduction due to ozone exposure.
  • Individuals with heart problems are also at risk. A recent EPA publication states that "There is limited, new evidence supporting associations between short-term ozone exposures and a range of effects on the cardiovascular system."
  • Healthy adults, as confirmed by many laboratory and "real world" ozone exposure studies are also at risk. People who exercise or otherwise participate in activities that increase their respiratory rate, respond much more severely to ground-level ozone exposure than people at rest. This means that adults exercising outdoors, construction workers and other outdoor workers are at risk during the summer months.

How do I know when ground-level ozone concentrations are high?

Ground-level ozone concentrations tend to be especially high during the summer months when the weather is hot and sunny. DEP staff have developed a procedure to inform the public about expected ground-level ozone readings. Each afternoon from May 1st through September 15th, Maine DEP staff retrieve and review monitored ozone data and weather forecast information. Staff then develop ground-level ozone forecasts for the following day. Whenever unhealthy ozone concentrations are expected, the forecast contains an "advisory" message. The forecast is made available to the public on a daily basis in the following ways:

  • 24-hour toll free Air Quality hotline: 1-800-223-1196
  • Online in this site - daily forecasts
  • EnviroFlash -- Email and text message alert system established by EPA in cooperation with MEDEP.
  • Local Media

How can I get additional information?

Contact DEP Bureau of Air Quality staff at DEP offices in:

Augusta: Tyson Building, AMHI, (207)287-2437
Bangor: 106 Hogan Road, (207)941-4570
Portland: 312 Canco Road, (207)822-6300
Presque Isle: 1235 Central Drive, (207)764-0477

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