Planning >> Air Awareness >> Air Quality Forecast Center >> Air Quality, Particle Pollution, and Ozone: Frequently Asked Questions
Air Quality, Particle Pollution, and Ozone: Frequently Asked Questions
Air Quality: General
What is air pollution?
What's the problem?
What air pollutants are regulated?
How do we know how much pollution is in the air?
How polluted is North Carolina's air?
What is the color-coded Air Quality Index and how is it used?
What is an Air Quality Action Day?
What can I do to improve North Carolina's air quality?
What is the Air Quality Coalition?
What is North Carolina doing to inform citizens about air pollution and its effects?
Where can I get real-time air quality information?
Where can I get historical air quality data?

Particle Pollution
What is particle pollution?
Where does particle pollution come from?
How do particles affect human health?
Who is affected by particle pollution?
What are the symptoms of particle pollution exposure?
What level of exposure to particulates is considered unhealthy?
How can I reduce my risk from particle exposure?
What time of year is particle pollution a problem?
What time of day are particle pollutions levels high?
What areas of N.C. have a particle pollution forecast?
Where can I find the particle pollution forecast?
How can I receive the particle pollution forecast directly?
What can I do to reduce particle pollution?
   Ozone
What is ozone?
Is ozone good or bad?
Is ozone the same thing as smog?
What North Carolina areas have an ozone problem?
How is ozone formed?
Why is ground-level ozone a problem?
What is the ground-level ozone standard in NC?
What does "ppm" mean?
What are the health effects of ground-level ozone?
What are the harmful environmental effects of ozone pollution?
How do weather conditions affect ground-level ozone?
When is the ground-level ozone season in NC?
What time of day are ground-level ozone levels the highest?
When is it best to do exercise outdoors during ozone season?
What is the ozone forecast?
When are the ground-level ozone forecasts issued?
Is there a ground-level ozone forecast for my area?
Where can I find the ozone forecast?
How can I receive the ground-level ozone forecast directly?
How can I take action to reduce ozone pollution?
Where can I find more air quality information?

What is air pollution? [Back to Top]
Air Pollution is a general term for many different substances in the air. Pollution generally describes a man-made substance that is harmful to human health, to wildlife and plant populations, or to other parts of the environment. Some pollutants are completely man-made and don't occur naturally in the environment. Some substances occur in nature, but are also produced in large amounts by human activities. These substances are considered pollutants because, in the higher concentrations produced by humans, they are harmful to human health and/or the environment. An example of this type of pollutant is ground-level ozone, which occurs naturally in very small amounts but is harmful in the concentrations that is formed by other pollutants produced by humans.

What's the problem? [Back to Top]
Air pollution can harm people's health and damage the environment. Air pollution can lead to breathing problems such as asthma and emphysema. Too much exposure to pollution during childhood can permanently reduce lung function. Some types of air pollution also can cause heart problems. Air pollution can harm you even if you can't see it or smell it. It also can hurt trees and wildlife, cause haze that blocks scenic views, and contribute to water pollution and climate change.

The two biggest air quality problems in North Carolina are ground-level ozone (the main ingredient in "smog") and particle pollution. Both pollutants are caused mainly by emissions from cars and trucks, and from the coal-burning power plants that supply most of our electricity. On many days in 2008 in our urban areas, the air was "unhealthy" to breathe for some or all people because of these pollutants. Smoke from outdoor burning and wildfires also contributes significantly to ozone and particle pollution.

Even with cleaner cars and other new technology, our air could get worse as our population grows, endangering our health and reducing our quality of life. The good news is that by being mindful of our daily activities, we can make a few simple changes to help us all breathe easier.

What air pollutants are regulated? [Back to Top]
Under the authority of the Federal Clean Air Act, passed in 1970 and amended in 1990, the U.S. Environmental Protection Agency (EPA) sets standards, or criteria, for six pollutants that are deemed harmful to human health and the environment. These "criteria pollutants" are nitrogen dioxide, sulfur dioxide, lead, carbon monoxide, ground-level ozone and particulate matter. The EPA's primary standards protect human health, and secondary standards for some pollutants protect public welfare and the environment. Other hazardous or toxic airborne chemicals are also regulated by the Federal government and North Carolina.

How do we know how much pollution is in the air? [Back to Top]
The Clean Air Act requires states to monitor levels of all criteria pollutants by using special monitoring equipment, and the monitor readings are reported to the EPA. The NC Division of Air Quality's Ambient Monitoring Section is responsible for monitoring the air in most of North Carolina. You can find peak air quality monitor readings for the past 24-36 hours, as well as statistical summaries and reports of past air quality, at the Ambient Monitoring Section's website. NCDAQ also forecasts daily air quality for many areas of North Carolina. These air quality forecasts give you warning of high pollution levels and can help you plan your activities to protect your health and the environment.

How polluted is North Carolina's air? [Back to Top]
North Carolina air quality is better than the federal standard for four of six criteria pollutants: nitrogen dioxide, sulfur dioxide, lead, and carbon monoxide. However, several areas in North Carolina violate the ground-level ozone standard as well as the fine particulate matter annual standard. Because air pollution levels are often influenced by weather conditions, some years are worse than others. In 2002, a hot, dry year, we experienced 29 Ozone Action Days of air quality code orange or red in the Triangle, 31 in the Triad, and 36 in the Charlotte area. That's about a month of unhealthful air conditions in each of North Carolina's three major population centers. The Division of Air Quality's Ozone Forecasting Center has compiled historical statistics of ozone levels in North Carolina's ozone forecast areas.

What is the color-coded Air Quality Index and how is it used? [Back to Top]
The Air Quality Index (AQI) is a tool used to report levels of ozone, particles and other pollutants in the air to the public. The AQI scale is divided into five color-coded categories, each corresponding to a different level of health concern ranging from green (good) to purple (very unhealthy). Greater AQI values correspond to greater concentrations of air pollution and indicate greater health danger.

The air quality color codes are:


AQI Color Code Air Quality AQI Number
Green Good 0 to 50
Yellow Moderate 51 to 100
Orange Unhealthy for Sensitive Groups 101 to 150
Red Unhealthy 151 to 200
Purple Very Unhealthy 201 to 300

The AQI color codes are used for both air quality forecasts and for air quality reporting. The forecast, available year-round in the Triad and Charlotte, and April 1 through October 31 in Asheville, Fayetteville, Hickory, and the Triangle, predicts anticipated pollution levels using the AQI color code. Air quality reports give either current pollution levels detected by monitors or air pollution levels that have already occurred, usually during the previous day. For reports of recent air quality levels in many areas of North Carolina, visit the DAQ ozone and particulate matter monitoring website or call 1-888-AIRWISE (1-888-247-9473). Reports of current and recent air quality levels in Mecklenburg County are found at the Mecklenburg County air quality monitoring website or by calling 704-333-SMOG (7664).

What is an Air Quality Action Day? [Back to Top]
An Air Quality Action Day is announced when pollution levels are forecasted to be Code Orange, Red or Purple (levels above the Federal health standard). On Air Quality Action Days, citizens are asked to take ACTION to reduce air pollution and to protect their health. From April 1 through October 31, most Air Quality Action Days will be for ozone, although a few code orange particulate days may occur during this period. From April 1 to October 31, most Air Quality Action Days will be for ozone, although a few code orange particulate days may occur during this period. From November 1 - March 31, Air Quality Action Days during this period should only be for particles.

What can I do to improve North Carolina's air quality? [Back to Top]
Ozone and particle pollution, the two biggest air quality concerns in North Carolina, come from many of the same sources, primarily motor vehicles and industry (including power plants). Our individual activities create air pollution, and all of us have the power to improve air quality through our actions. Try some of the following:

  • Leave your car at home. Take the bus, car pool, van pool, walk or ride your bike to your destination.
  • Don't drive to lunch. Take a meal or walk to a nearby restaurant instead of driving out to eat during the workday.
  • Drive right. When you do drive your car, use cruise control whenever practical and stay within the speed limit. Avoid sudden stops and starts. Plan ahead and combine short trips whenever possible to avoid cold starts. Your vehicle may be your single biggest impact on air quality. Make air quality a priority by factoring emissions and fuel efficiency into your vehicle purchasing decisions. Find how vehicles compare by using the EPA's Green Vehicle Guide or the US Department of Energy's fuel economy website .
  • Keep vehicles maintained. Keep your car, boat, and lawn equipment tuned up and follow your car's maintenance schedule. Engines that are well maintained are more fuel-efficient and cause less pollution.
  • Check your tire pressure. Keep your tires properly inflated; you'll save gas and reduce tire wear, too.
  • Don't idle. Avoid idling in drive-through lanes - park and walk in instead. Idling your vehicle wastes gas and increases pollution, and idling can damage your car more than shutting off and re-starting your engine.
  • Refuel at dusk. Postpone refueling your car until after 6 p.m. on Air Quality Action Days. This reduces the emissions during the peak daylight hours when ozone formation is most likely.
  • Don't top off your tank. When refueling your vehicle, stop at the click to avoid spilling gas and polluting the air and surface water.
  • Reduce use of gasoline-powered lawn equipment.The small engines in lawn care equipment are major polluters. Use hand-powered or electric lawn care equipment whenever possible, and consider landscaping to reduce the amount of grass on your property. On Air Quality Action Days, wait until after 6:00 p.m. to use gas-powered lawn equipment.
  • Conserve electricity. In the summer, set your air conditioning at the highest comfortable temperature (try 78 degrees). During winter, try a setting of 68 - 70 degrees to reduce electricity use by your heat pump. Reduce wintertime particulate matter pollution from oil furnaces by keeping them well maintained. Use ceiling fans to increase both cooling and heating efficiency. Turn off appliances when not in use. Look for the Energy Star label when purchasing major appliances.
  • Try something different. Use water-based paints and cleaners instead of solvent-based products.

What is the Air Quality Coalition? [Back to Top]
The Air Quality Coalition is a partnership of businesses, governments, and organizations motivated to improve North Carolina's air quality, as well as the quality of life of their employees and members. Coalition organizations inform their employees about air quality by distributing the air quality forecast and providing education about air quality issues and actions. Some Coalition organizations help their employees improve air quality by providing incentive programs for carpooling and transit. Over 500 partners participate in local Air Quality Coalitions in the Asheville, Charlotte, Hickory, Triad, and Triangle areas, educating thousands of people about air quality. If you'd like your organization to become a member of the Air Quality Coalition, send an email to Air.Awareness@ncdenr.gov.

What is North Carolina doing to inform citizens about air pollution and its effects? [Back to Top]
The NC Air Awareness Program was created to inform North Carolina's citizens about air pollution and its effects. The program is an active partnership between the North Carolina Division of Air Quality, county environmental agencies, health departments, local governments, transit providers, businesses, citizen organizations, educators, and the media. The Air Awareness program works to educate the public about air quality issues through the internet, hotlines (1-888-RU4NCAIR), brochures, school visits, public events, local media coverage, and through the Air Awareness Coalition. The program seeks to inform citizens as to how their daily actions affect air quality, and how they can protect their health and the health of their environment by making simple lifestyle adjustments. It's just a matter of taking the time to Think, Act and Breathe.

Where can I get real-time air quality information? [Back to Top]
Statewide air quality information is available from the N.C. Division of Air Quality's website. Current information for Mecklenburg County monitors is available from the Mecklenburg County Air Quality agency or by calling 704-333-SMOG (7664). The N.C. Division of Air Quality is currently working to make more real-time air quality information available on our website.

You can also find maps of current air quality conditions for areas around the country, as well as air quality forecasts, on the EPA's AIRNow website.

Where can I get historical air quality data? [Back to Top]
You can find peak air quality monitor readings for the past 24-36 hours, as well as statistical summaries and reports of past air quality, at the N.C. Division of Air Quality Ambient Monitoring Section's website. For data from locations nationwide, visit the EPA Office of Air Quality Planning and Standards Air Pollution Monitoring website . Ozone forecast verifications, past ozone concentration nformation, and ozone monitor statistics are available through the DAQ on the Ozone Concentration Data website.

What is particle pollution? [Back to Top]
Particle pollution, also known as particulate matter pollution or PM, is a mixture of tiny solids and liquid droplets suspended in air. Airborne particles are the main ingredient in haze, smoke and airborne dust. Particles are made up of a variety of components and may include acids, nitrates, sulfates, organic chemicals, metals, elements from soil or dust, or allergens (for example, fragments of pollen or mold spores). Particles come in a wide range of sizes. Those less than 10 micrometers in diameter are so small that they can be inhaled into the lungs, potentially causing serious health problems. For comparison, ten micrometers is much smaller than the width of a single human hair, which is ~70 micrometers in diameter. Particles less than 2.5 micrometers in diameter are called "fine" particles and are of special concern because they can penetrate deeply into the lungs. Particles between 2.5 and 10 micrometers in diameter are referred to as "coarse" particles.

Where does particle pollution come from? [Back to Top]
Some particles are directly emitted into the air, like dust, or the "soot" particles in diesel exhaust. Other tiny particles are indirectly formed when chemicals like sulfates, nitrates, and carbon condense and combine in the air. Sources of fine particles include all types of combustion from a number of sources, including cars and trucks, power plants, other industry, and residential fireplaces and wood stoves. Because cars and trucks are a major source, particle levels are generally higher near busy roadways. Diesel-powered vehicles and engines contribute more than half of motor vehicle fine particulate emissions. Indoor sources of particle pollution include smoke from tobacco, candles, wood stoves, fireplaces, and emissions from natural gas stoves. Sources of coarse particles include crushing or grinding operations, dust stirred up by vehicles traveling on unpaved roads, and windblown dust.

How do particles affect human health? [Back to Top]
When inhaled, particles can be deposited in the airways or deep in the lungs. Once deposited, several things may happen. Particles may be cleared by the body's natural defense mechanisms, they may accumulate on the surface where they deposit, or they may be absorbed into the underlying tissues. The soluble components of fine particles, along with very small ("ultrafine") particles, may enter the bloodstream. Some particles may react chemically in the body; others remain in their original form.

The most serious effects of particles are associated with heart or lung disease. Numerous studies have linked particle pollution to increased admissions to hospitals and emergency room visits, and even to death from heart or lung diseases. Short-term exposure has been linked to aggravation of lung diseases, including asthma attacks and acute bronchitis. In people with heart disease, particles have been linked to heart attacks and cardiac arrhythmias (Irregular heart rhythms). Recent evidence suggests that some of these effects may result from very short-term exposures, possibly as short as an hour. Epidemiologists have found that mortality rates and hospitalization rates increase when particle pollution concentrations rise even a moderate amount. Epidemiologists link thousands of yearly fatal heart attacks in the U.S. to particulates.

A 16-year study published in March 2002 in the Journal of the American Medial Association provides evidence that long-term exposure to fine particles significantly increases the risk of illness and death from lung cancer and heart disease. The level of lung cancer risk associated with exposure to fine particles emitted by coal-fired power plants, factories and diesel trucks is comparable to the risk posed by long-term exposure to second-hand smoke from cigarettes.(1) American Cancer Society and Harvard University epidemiological studies recently showed that people living in more polluted cities had an increased risk of premature death compared to those in cleaner cities.

Particle exposure might also increase susceptibility to bacterial or viral respiratory infections, leading to increased risk of pneumonia in vulnerable individuals. In the presence of pre-existing heart disease, acute bronchitis or pneumonia induced by air pollutants might precipitate congestive heart failure.

In healthy children and adults, exposure to elevated particle levels for short periods of time may cause minor irritation. Most healthy people will recover quickly from these effects and are unlikely to experience long-term health problems. However, long-term exposure to particles has been associated with reduction in lung function and the development of chronic bronchitis.

(1) Pope et al. 2002. Lung Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. J. Am. Med. Assoc. 287(9):1132-1141.

Who is affected by particle pollution? [Back to Top]
Everyone's health can be at risk when particle pollution levels are high, but some groups of people are also at risk at lower levels, such as those with heart or lung disease, older adults (men over 45 and women over 55), and children.

People with heart or lung diseases such as congestive heart disease, coronary artery disease, asthma, or chronic obstructive pulmonary disease (COPD) are at risk because particles can aggravate these conditions. In addition, the obstructed airflow in people with COPD may cause more particles to deposit in their lungs. People with diabetes may be at increased risk of serous effects, possibly because of underlying cardiovascular disease.

Older adults are at increased risk, possibly because they are more likely to have either diagnosed or undiagnosed heart or lung disease or diabetes.

Children may be more vulnerable to particles because their lungs are still developing, and they breathe more air in relation to body weight than do adults. In addition, they spend more time at higher activity levels, and are more likely to have asthma or acute respiratory diseases.

Factors that increase the risk of heart attack may also increase your risk from particles. These include age, family history of heart disease, smoking, high blood pressure, high blood cholesterol, obesity, physical inactivity and diabetes. The risks of health effects are increased by physical activity during periods of elevated particle pollution. When you are physically active, you breathe faster and more deeply, taking more air and more particles into your lungs. Scientists do not yet know if pregnant women are at increased risk from particle pollution. Studies suggest that breathing high particle levels over long periods of time may be associated with low-birth-weight infants, pre-term deliveries, and fetal and infant deaths.

What are the symptoms of particle pollution exposure? [Back to Top]
If you have lung disease, you may not be able to breathe as deeply or as vigorously as normal, and you may experience respiratory symptoms such as coughing, chest discomfort, wheezing, shortness of breath, and unusual fatigue. If you experience these symptoms, you should reduce exposure and activity level, and follow the advice of your doctor. If you have asthma, you should already have an asthma action plan, but you may need to follow it more carefully when particle levels are high.

If you have heart disease, you can have serious effects, such as heart attacks, with no warning symptoms. The absence of symptoms does not mean that you are safe. If you do experience symptoms - such as chest pain or tightness, palpitations, shortness of breath, or unusual fatigue - contact your doctor as these symptoms may indicate a serious problem.

Even if you are healthy you may experience temporary symptoms from exposure to elevated levels of particles. Symptoms may include; irritation of the eyes, nose and throat, coughing; phlegm; chest tightness; and shortness of breath.

What level of exposure to particulates is considered unhealthy? [Back to Top]
People have experienced health problems from exposure to particles over long periods (years) and from periods as short as 1 to 24 hours. Epidemiological studies have reported a linear relationship between exposure and effects; higher concentrations of particles have a greater effect on the health of populations. Scientists have not been able to identify a threshold below which health effects do not occur. According to the World Health Organization, long-term epidemiology studies show that the risk of premature deaths starts to increase when the annual average of fine particle concentrations exceeds10 micrograms per cubic meter. The EPA has set an annual and a 24-hour standard for fine particulate pollution to protect human health. The annual standard is 15 micrograms per cubic meter. This represents particle levels averaged over an entire year, and is designed to protect the public from long-term exposure. The 24-hour standard is 35 micrograms per cubic meter, and protects against short-term exposure to higher particle levels.

How can I reduce my risk from particle exposure? [Back to Top]
Your chances of being affected by particles increase the longer you are active outdoors and the more strenuous the activity you engage in. If you're involved in an activity that requires prolonged or heavy exertion, you can reduce the time you spend on the activity or substitute another activity that requires less exertion; for example, go for a walk instead of a jog. You can also plan outdoor activities when and where particle levels are lower. In general, levels of particles and other pollutants are higher near busy roadways, so avoid heavy exertion - like jogging or biking - in these areas.

Daily air quality forecasts give notice of anticipated high particle levels. People in at-risk groups should take special care to reduce exposure at Code Orange air quality levels or higher, and everyone should exercise caution at code red levels.

Particle levels can sometimes be elevated indoors, especially if particles in the outdoor air are elevated and there are additional indoor sources, such as tobacco smoke. Certain filters are available that can help reduce particle levels indoors. Ozone-producing air cleaners (sometimes called "activated oxygen" air cleaners) should not be used in occupied spaces as they may cause unhealthy levels of ozone to accumulate. You can also reduce indoor sources of particles by eliminating tobacco smoke and reducing the use of candles, wood-burning stoves and fireplaces.

What time of year is particle pollution a problem? [Back to Top]
Unlike ozone, particle pollution occurs year-round, and particle pollution levels can be high inside or outside. When particle pollution levels are high it is important to limit physical activity, even if that activity occurs indoors. Unusual events sometimes increase particle pollution to high levels. Occasionally a plume of smoke from a distant forest fire will elevate local particle levels. After the December 2002 ice storm, many Triangle area residents without electricity burned wood for warmth. At the same time, an atmospheric inversion concentrated the wood smoke, resulting in Code Red particle pollution levels in the Triangle.

What time of day are particle pollutions levels high? [Back to Top]
Unlike ground level ozone pollution, particle pollution levels can be high in the morning or in the afternoon. It is important to know the Air Quality Index Color Code forecast for the day and limit or avoid activity - inside or out, morning or evening - on days when particulate pollution levels are high.

What areas of N.C. have a particle pollution forecast? [Back to Top]Particle pollution forecasts are available year-round in Charlotte, Fayetteville, the Triangle, the Triad, Hickory, and the Asheville valleys.

Where can I find the particle pollution forecast? [Back to Top]
Daily air quality forecasts will warn you of expected high particle levels. During the warm-weather season of April 1 through October 31, the forecasts will also warn of high ozone levels. You can find the forecast in the weather section of your local newspaper or during the weather segment of your local television news. You may also hear it on some radio stations. Some national media, such as USA Today and The Weather Channel, also provide air quality information.

You can find the particle forecast at NC DAQ Air Quality Forecast Center website for Asheville, Charlotte, Hickory, Fayetteville, and the Triangle, and at the Forsyth County Environmental Affairs website for the Triad. You can also call 1-888-RU4NCAIR (1-888-784-6224) to hear forecasts for both areas. Forecasts are issued at approximately 3:00 each day, and predict air quality for the following day. In Mecklenburg County, you can find real-time air quality information for selected monitors at the Mecklenburg County air quality monitoring website . Monitor data using the state network can be found at the Ambient Monitoring current data webpage. This information will let you know when local particle levels are already high.

How can I receive the particle pollution forecast directly? [Back to Top]
Any individual or organization can receive the forecast by email through EnviroFlash. EnviroFlash is sponsored by the EPA and provides air quality information such as forecasts and action day notifications via email for your area of interest. To register for EnviroFlash, visit the EnviroFlash sign-up page . Please note that air quality forecasts are not provided for all regions. The Division of Air Quality provides forecasts for areas known to have instances of poor air quality, while areas of generally good air quality do not receive forecasts. If your location is not near a forecast location, you will be notified during the signup process.

If you are with a business, government agency, or organization, consider signing up for your local Air Quality Coalition. Coalition members distribute the Air Quality Action Day forecasts to their employees or organization members, and provide air quality education. In this way, Coalition members help to improve both air quality and public health. Contact Air.Awareness@ncdenr.gov or call 1-888-RU4NCAIR for more information.

What can I do to reduce particle pollution? [Back to Top]
Because particle sources include vehicles and power plants, you can help reduce particle pollution by driving less, keeping your car well maintained, and conserving energy. Some specific ways to help are found near the beginning of this document.

One important way to help reduce particle levels is by avoiding backyard burning, sometimes called open burning. Burning non-vegetative trash is illegal everywhere in North Carolina, and burning yard waste is illegal in many municipal areas with yard waste pickup. Although burning yard waste may seem harmless, the particle-rich smoke from your backyard fire could harm others in your community, especially if they have heart or lung problems. Compost or mulch your yard waste instead.

What is ozone? [Back to Top]
Ozone is an ionic form of oxygen with 3 oxygen atoms (O3). By contrast, the form of oxygen we breathe has two atoms (O2). The extra oxygen atom makes ozone very unstable and thus highly reactive. Ozone occurs naturally in the upper atmosphere, but is created by human activities at ground level. Ozone has the same chemical structure whether it occurs high above the earth or at ground level, and can be "good" or "bad," depending on its location in the atmosphere.

Is ozone good or bad? [Back to Top]
The naturally occurring ozone layer in the upper atmosphere, or stratosphere, protects the earth from the sun's ultraviolet radiation. Obviously, stratospheric ozone is "good" ozone, and the depletion of stratospheric ozone continues to be of major concern.

However, ozone does not occur naturally in the lower atmosphere, except in very small amounts. Most of the ozone at ground level is produced by human activities. Ground level or "bad" ozone is an air pollutant that damages human health, vegetation, and even man-made materials such as fabric and rubber.

Is ozone the same thing as smog? [Back to Top]
The term "smog" is often used to refer to ground-level ozone pollution. When you see or hear the word smog used in a news report about air pollution, you can usually assume that the report is referring to ozone pollution. Ozone combines with particle pollution to form the dirty-looking urban haze that many people think of as smog. So although ozone and smog are not the same thing, ozone is a necessary ingredient of smog. However, it's important to remember that ozone levels can be high even on a clear day with no visible "smog".

What North Carolina areas have an ozone problem? [Back to Top]
Typically, high ozone pollution levels occur in urban areas where there are lots of cars, industry and other sources of combustion. However, ozone can travel with the wind to rural areas and become a problem in those areas as well. In North Carolina, our greatest areas of concern are the Charlotte area, the Triad (Greensboro, Winston-Salem, and High Point), and the Triangle (Raleigh, Durham, and Chapel Hill). However, several other areas of North Carolina have a problem with high ozone levels and exceed (have higher values) than the EPA's 8-hour ozone standard.

How is ozone formed? [Back to Top]
Ground-level ozone forms when nitrogen oxides (NOx) react with volatile organic compounds (VOCs) in the presence of heat and sunlight.

VOCs, Volatile Organic Compounds or hydrocarbons, come from man-made sources such as cars, service stations, dry cleaners and factories as well as natural sources such as trees and other vegetation. Because VOCs are volatile, or highly reactive, they evaporate easily and typically have a strong smell. Fumes from gasoline, paint thinners and solvents, and even printer ink are all VOCs. Not all VOCs smell "bad". Some good smelling VOCs are the fragrances in perfumes, soaps, and other consumer products. Naturally occurring VOCs from trees and vegetation are sometimes called biogenic emissions, while man-made emissions are referred to as anthropogenic.

NOx is a byproduct of combustion, and comes from coal-fired power plants, industrial boilers, motor vehicles, lawn-care equipment and other sources that burn fuel. In some North Carolina urban areas, up to 70% of ozone-forming NOx comes from motor vehicles.

Efforts to control ozone focus on NOx because most of it comes from man-made sources that can be controlled. Reducing VOCs is less effective because pines, oaks and other trees that are so abundant in the South emit large amounts of hydrocarbons.

Most of the ozone in urban areas comes from local sources. However, winds can carry ozone from cities to surrounding rural areas and even to other states. Much of the ozone pollution at high elevations in the mountains of Western North Carolina is transported by winds from other states. In mountain valleys, however, ozone-forming pollution can come from both local and out-of-state sources.

Why is ground-level ozone a problem? [Back to Top]
Ozone is a strong respiratory irritant, and can cause serious health problems, especially for sensitive groups: children, people with asthma and other respiratory ailments, and anyone who works or exercises vigorously outdoors. Symptoms of ozone exposure can include coughing, throat irritation, chest pain, rapid and shallow breathing, and asthma attacks. Emergency room visits for asthma have increased as much as 36 percent on high ozone days, according to some studies. High childhood exposure to ozone pollution may reduce lifetime lung function. High ozone levels also damage vegetation, reducing growth rates and crop yields. More details on the health and environmental effects of ozone can be found later in this section.

What is the ground-level ozone standard in NC? [Back to Top]
The Federal standard for ground-level ozone is 0.075 parts per million (ppm), averaged over an 8-hour period. This is often referred to as the "8-hour standard" and replaces an older "1-hour standard" of 0.125 ppm. Levels of 0.076 ppm and above exceed the Federal ground-level ozone standard.

What does "ppm" mean? [Back to Top]
Parts per million, or ppm, is a ratio that describes how many parts of something you have per one million equally-sized parts of something else. So, with the 8-hour standard, the maximum healthy concentration of ground-level ozone is less than 1/10th of one part of ozone per one million parts of air.

These examples might help you understand:

  • If a pie is divided equally into 10 pieces, each piece would be a part-per-ten; i.e., one-tenth of the total pie. If the pie were cut into 100 pieces, each piece would be one part-per-hundred, or one percent, of the pie. If this pie is cut into a million pieces, each piece would be very small and would represent a millionth, or part per million, of the original pie. If each of the million minute pieces is cut into a thousand little pieces, each of these new pieces would be a part per billion of the original pie.
  • Four drops of ink in a 55-gallon barrel of water would produce an ink concentration of 1 ppm.
  • One drop of ink in one of the largest tanker trucks used to haul gasoline would represent 1 ppb.

What are the health effects of ground-level ozone? [Back to Top]
Ozone is a strong respiratory irritant. Short-term, infrequent exposure to ozone can result in throat and eye irritation, difficulty drawing a deep breath, and coughing. Long-term and repeated exposure to ozone concentrations above the Federal standard can result in reduction of lung function as the cells lining the lungs are damaged. Repeated cycles of damage and healing may result in scarring of lung tissue and permanently reduced lung function. Health studies have indicated that high ambient ozone concentrations may impair lung function growth in children, resulting in reduced lung function in adulthood. As lung function declines in older adults, individuals whose lung function is already below normal may be especially vulnerable to respiratory problems.

Asthmatics and other individuals with respiratory disease are especially at risk from elevated ozone concentrations. Ozone can worsen, and may trigger, asthma attacks. Ozone may also contribute to the development of asthma. A recent study published in the British medical journal The Lancet, found a strong association between elevated ambient ozone levels and the development of asthma in physically active children.(2)

All children are at risk from ozone exposure because they often spend a large part of the summer playing outdoors, their lungs are still developing, they breathe more air per pound of body weight, and they are less likely to notice symptoms. Children and adults who frequently exercise outdoors are particularly vulnerable to ozone's negative health effects, because they may be repeatedly exposed to elevated ozone concentrations while breathing at an increased respiratory rate.

(2) McConnell et al. 2002. Asthma in exercising children exposed to ozone: a cohort study. Lancet 359: 386-391.

What are the harmful environmental effects of ozone pollution?  [Back to Top]
Water Pollution: The nitrogen oxides that contribute to ozone pollution also fall back to the earth as nitrogen compounds, contributing to nutrient pollution of streams, rivers, and estuaries. As much as half of the nitrogen pollution in North Carolina's coastal waters may come from air pollution. Nutrient pollution contributes to algal blooms, reduced oxygen content of water, and fish kills.

Plant and Crop Damage: Ozone pollution can damage plant tissues, reducing growth rates and agricultural yields. It interferes with the ability of plants to produce and store food, making them more susceptible to disease, insects, other pollutants, and harsh weather. Ground-level ozone damages the foliage of trees and other plants, impacting the landscape of cities, national parks and forests, and recreation areas.

How do weather conditions affect ground-level ozone? [Back to Top]
Sunlight, temperature, atmospheric stability, and wind conditions all affect the formation and accumulation of ground-level ozone. Ultraviolet radiation from sunlight drives the reaction between NOx and VOCs to form ozone, so ozone pollution increases on clear or partly cloudy days. Like many chemical reactions, ozone formation increases as temperatures rise. In addition, temperature affects ozone-forming emissions (e.g., evaporative emissions of VOCs and biogenic emissions increase with high temperatures). Atmospheric stability (temperature change by height) controls the amount of vertical air mixing that takes place. Strong stability tends to reduce mixing (dilution) of ground-level ozone and ozone-forming emissions. During atmospheric inversions, air higher in the atmosphere is warmer than air below, preventing lower air from rising and mixing. Inversions thus concentrate air closer to the surface, sometimes resulting in higher ozone levels. Wind conditions affect the dispersal and dilution of air and pollutants. Calm or light winds allow more pollution to concentrate in an area. Upper-level winds are also important because they can transport ozone great distances during the overnight period. Ozone concentrations tend to be highest on sunny, hot days with little to no wind.

When is the ground-level ozone season in NC? [Back to Top]
Because hot, sunny conditions are needed for elevated ozone levels, ozone is only a problem during the warm-weather months. The ozone forecast season, when N.C. Division of Air Quality forecasts daily ozone levels, is April 1 to October 31.

What time of day are ground-level ozone levels the highest? [Back to Top]
Ozone begins forming in the morning and formation increases as temperatures increase during the day. Ozone accumulates through the day, especially when winds are calm. In most areas of North Carolina, ozone levels peak during mid-afternoon through early evening, when temperatures are hottest. Ozone levels decrease as the sun sets, 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.

When is it best to do exercise outdoors during ozone season? [Back to Top]
On Ozone Action Days, it's safest to exercise in the morning, when ozone levels are lowest. 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.

By paying attention to the daily ozone forecast, you can plan your exercise schedule. On Ozone Action Days of Code Orange and above, try to schedule exercise for the morning, and avoid strenuous exercise in the afternoon. Although ozone levels are generally not as low at dusk as in the morning, ozone levels during dusk and evening are usually safe for exercise. On Code Green days, you are safe exercising any time of the day, and most people are safe exercising on Code Yellow days as well. On "high" Code Yellow days when the AQI is predicted to be close to 100, very sensitive people may need to limit or avoid afternoon exertion.

If you are considering exercising at high elevations in the mountains, the Asheville Ridge Tops forecast will alert you to days when ozone levels may be elevated during daytime and nighttime hours.

What is the ozone forecast? [Back to Top]
The NC Division of Air Quality issues a ground-level ozone forecast every day from April 1 through October 31 that consists of an Air Quality Index (AQI) forecast and a corresponding color code. The color code and AQI value predict the maximum 8-hour ozone concentration for the following day. This information is distributed via email, media outlets, and the North Carolina Forecast Center web site. The ground-level ozone forecast allows citizens not only to plan outdoor activities to protect their health, but also to take action to reduce ozone-forming emissions.

When are the ground-level ozone forecasts issued? [Back to Top]
Ground-level ozone forecasts are issued everyday from April 1 through October 31h at 3:00 pm EDT. A "forecast discussion", also issued at 3:00 pm EDT, provides a detailed description of the current ozone and meteorological conditions which the forecaster has considered in making the forecast. A "morning edition" is available around 10:00 am EDT each day. The morning edition provides additional information specifying whether the current forecast appears to be on track.

Is there a ground-level ozone forecast for my area? [Back to Top]
The NC Division of Air Quality issues ground-level ozone forecasts for the Asheville (Ridge Tops and Valleys), Charlotte, Fayetteville, Hickory, Rocky Mount, and the Triangle regions of North Carolina. Additionally, the Forsyth County Environmental Affairs Department issues an air quality forecast for the Triad area. There is a ground-level ozone forecast for your area if you live or work in one of the counties associated the following forecast regions:

  • Asheville: Buncombe, Haywood, Henderson, Jackson, Madison, Transylvania, Swain, and Yancey Counties.
  • Hickory: Alexander, Catawba, Southeastern Burke and Southeastern Caldwell Counties.
  • Charlotte: Cabarrus, Gaston, Lincoln, Mecklenburg, Rowan, Union, and Southern Iredell Counties, NC; and York County SC.
  • The Triad: Alamance, Caswell, Davidson, Davie, Forsyth, Guilford, Randolph, Rockingham, and Stokes Counties.
  • The Triangle: Chatham, Durham, Franklin, Granville, Johnston, Orange, Person, Vance, and Wake Counties.
  • Fayetteville: Harnett and Cumberland Counties.

Where can I find the ozone forecast? [Back to Top]
Between April 1 through October 31, look for the ozone forecast in the weather section of your local newspaper and during the weather segment of your local television news. You may also hear it on some radio stations. Some national media, such as USA Today and The Weather Channel, also provide air quality information.

You can find the forecast at the NC DAQ Air Quality Forecast Center website for all areas except the Triad, and at the Forsyth County Environmental Affairs Department for the Triad. You can also call 1-888-RU4NCAIR (1-888-784-6224) to hear forecasts for all areas. Forecasts are issued at approximately 3:00 each day, and predict air quality for the next day.

How can I receive the ground-level ozone forecast directly? [Back to Top]
Any individual or organization can receive the forecast by email through EnviroFlash. EnviroFlash is sponsored by the EPA and provides air quality information such as forecasts and action day notifications via email for your area of interest. To register for EnviroFlash, visit the EnviroFlash sign-up page . Please note that air quality forecasts are not provided for all regions. The Division of Air Quality provides forecasts for areas known to have instances of poor air quality, while areas of generally good air quality do not receive forecasts. If your location is not near a forecast location, you will be notified during the signup process.

If you are with a business, government agency, or organization, consider signing up for your local Air Quality Coalition. Coalition members distribute the Air Quality Action Day forecasts to their employees or organization members, and provide air quality education. In this way, Coalition members help to improve both air quality and public health. Contact Air.Awareness@ncdenr.gov or call 1-888-RU4NCAIR for more information.

How can I take action to reduce ozone pollution? [Back to Top]
Because the biggest source of ozone pollution in most areas is cars and trucks, taking steps to reduce driving your car will be the most helpful. Conserving electricity will reduce ozone pollution resulting from power plant emissions. A list of specific things you can do is near the top of this document.

Your business, citizen organization, or agency can help reduce ozone pollution by joining the Air Quality Coalition. Coalition partners distribute the Air Quality Action Day forecasts to their employees or organization members, and provide air quality education. The combined efforts of over 500 Coalition partners statewide reach many thousands of people, improving both air quality and public health. Contact Air.Awareness@ncdenr.gov or call 1-888-RU4NCAIR for more information.

Where can I find more air quality information? [Back to Top]