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Ozone Information


What is ozone?  
Ozone is a highly reactive gas that forms in the atmosphere when three (3) atoms of oxygen are combined (O3) through a chemical reaction. In contrast, the oxygen gas we breathe is chemically formed from two (2) atoms of oxygen (O2) and is stable. Ozone is not emitted directly into the air but, at ground level, is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone has the same chemical structure whether it occurs high above the earth or at ground level, and it can be "good" or "bad," depending on its location in the atmosphere.


Is ozone good or bad?
Ozone occurs in two layers of the atmosphere. The layer surrounding the earth's surface is the troposphere. All animal and plant life is contained within the troposphere. Here, ground level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. Ground-level ozone is primarily formed as a result of human activities. The troposphere extends to a level about 10 miles up, where it meets the second layer of the atmosphere, the stratosphere. In this second layer of the atmospheric, the stratospheric or "good" ozone layer extends upward from about 10 to 30 miles. The stratospheric ozone layer naturally occurs and protects life on Earth from the sun's harmful ultraviolet rays (UV-b).

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Where is ozone a problem?  
Ground-level ozone is a problem anywhere it exists. Typically, it is produced in urban areas where there are lots of cars, industry, and other sources of combustion. Ozone can travel with the wind to other places and become a problem there, too. In North Carolina, our greatest areas of concern are the greater Charlotte area, the Triad (Greensboro, Winston-Salem, and High Point), and the Triangle (Raleigh, Durham, and Chapel Hill). Each of these areas has had a violation of the federally enforced one-hour ozone standard in previous years. Future growth projections in population and vehicle use indicate that these areas along with other communities of North Carolina could potentially violate the proposed eight-hour federal standard.


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How do we test for ground-level ozone?
Ground-level ozone can be detected by a number of methods, but sensitive ozone measurements require a highly specialized piece of chemical analysis equipment. The ozone monitors operated and maintained by the MCAQ use an ultra-violet absorption technique to determine the ground-level ozone concentration to the nearest one-hundredth of a part per million (ppm) or the nearest part per billionth (ppb).

MCAQ operates three ozone monitors in the county, one at Arrowood Industrial Park, one at Garinger High School, and one near the Mecklenburg/Cabarrus County line near Lowes Motor Speedway.

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What are the health effects of ground-level ozone?
Ground-level ozone can cause acute respiratory problems, aggravate asthma, temporarily decrease lung capacity (from 15 to 20 percent in a healthy adult), cause inflammation of lung tissue, increase hospital admissions and emergency room visits, and impair the immune system making you more susceptible to respiratory illness (e.g. bronchitis, and pneumonia). People may notice that they cough more or have trouble breathing on high ozone days.

Repeated exposure to ozone pollution may cause permanent damage to the lungs. Even when ozone is present in low levels, inhaling it triggers a variety of health problems including chest pains, coughing, nausea, throat irritation, and congestion. It also can worsen bronchitis, heart disease, emphysema, and asthma, and reduce lung capacity.

Healthy people also experience difficulty in breathing when exposed to ozone pollution. Because ozone pollution usually forms in hot weather, anyone who spends time outdoors in the summer may be affected, particularly children, the elderly, outdoor workers and people exercising. Millions of Americans live in areas where the national ozone health standards are exceeded.

Ground-level ozone damages plant life and is responsible for 500 million dollars in reduced crop production in the United States each year. It interferes with the ability of plants to produce and store food, making them more susceptible to disease, insects, other pollutants, and harsh weather. "Bad" ozone damages the foliage of trees and other plants, ruining the landscape of cities, national parks and forests, and recreation areas.

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When is the ozone season in NC?
The ground-level ozone season occurs during the warm-season months, when the days are warmer and longer. The period of May 1st through September 30th is considered the ground-level ozone season in North Carolina. Monitoring for ground-level ozone starts at the beginning of April and continues the monitoring through the end of October.

During the warm-season in North Carolina, the northern hemisphere of the earth is tilted toward the sun. The sun's rays hit the ground more directly and warm the atmosphere more efficiently than in the wintertime. This tilt toward the sun also results in an increase of daylight hours. The warmer and longer days allows for more ground-level ozone production than at any other time of the year.

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What time of day are the ozone levels the highest?
Sunlight is necessary to start the chemical reactions that form ozone, and heat is important to make the chemical reactions more efficient. Ozone is primarily a problem during the summer months when long days deliver plenty of sunlight and when temperatures are warmest. In most areas of North Carolina, ozone levels peak during mid-afternoon through evening, when temperatures are higher, then drop at night, and are lowest around dawn. However, at high elevations (above 4,000 feet) in the mountains, ozone levels can remain high throughout the day and actually reach their highest values overnight.

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When is it best to  exercise outdoors during the ozone season?
It is safe on ozone action days to exercise in the morning, because ozone does not usually reach unhealthy levels until the afternoon when temperatures are the hottest. Morning is a good time for biking, walking, jogging or other types of strenuous outdoor activities. At high elevations in the mountains, ozone levels can remain high throughout the day and night during bad air events - so people should limit outdoor activities if they notice signs of problems such as coughing and breathing difficulty

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What can I do to help reduce the occurrence of ground level ozone?







  • Take your lunch.
    Or walk to a nearby restaurant - this reduces the number of vehicles on the road during the daylight hours.  
  • Drive it right.
    When you do drive your car, use cruise control whenever practical and stay within the speed limit. Avoid sudden stops and starts, and avoid idling for long periods of time. Plan your trips so that you combine short trips whenever possible.  
  • Do it at dusk.
    Postpone refueling your car until after 6 pm. This reduces the emissions during the peak daylight hours when ozone formation is most likely. Don't "top off" the tank, that is stop adding gasoline, after the pump has automatically shut itself off. This will avoid spills of gasoline and unnecessary VOC emissions.  
  • Stay tuned.
    Keep your car, boat, and lawn equipment tuned up. Engines that are well-maintained are more fuel efficient and emit less air pollutants. Get a tune up a once a year tune up. After all it makes good economical and environmental sense.  
  • Leave your car.
    Take the bus, car pool, van pool, walk or ride your bike to your destination.  
  • Conserve electricity.
    When at home, set your thermostat at the highest temperature at which you are comfortable (try 78 degrees). When everyone is away or asleep, set the thermostat at a warmer temperature. Use a ceiling fan to circulate the cool air. Turn off appliances when not in use.  
  • Cut it out.
    Try not to cut the grass. Use hand-powered or electric lawn care equipment whenever possible. If you must use gas-powered equipment, wait until after 6:00 pm. 
  • Try something different.
    Use water-based paints and cleaners instead of solvent-based products.

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