Air Quality


In most summers North Carolina's weather is dominated by the "Bermuda High" pressure system. This gives calm, virtually cloudless conditions where any pollution placed into the atmosphere remains suspended for an extended period of time. Fortunately, compared to many other states, North Carolina does not support activities which emit great quantities of pollution. But automobile traffic in the major cities, along with some paper producing and energy generation plants can cause local problems for short periods of time. Additionally, with our winds coming predominantly from a westerly direction, North Carolina also receives pollution from a suite of upwind states. On occasion this can severely reduce visibility in the western mountains, and has been regarded as a major contributor to the presence of acid rain on some of the highest peaks.

Air Quality Index

The Environmental Protection Agency has developed an Air Quality Index (AQI) that gives the public a general idea of the condition of the air and any health concerns associated with air quality. For each pollutant that the EPA applies this index to, it defines a range of pollutant amount that it deems to pose little health risk, moderate health risk, etc., and uses a mathematical formula to convert that to a scale of 500. The color-coded AQI for these pollutants is generalized below:

Air Quality Index (AQI) Values Levels of Health Concern Colors
0 to 50 Good Green
51 to 100 Moderate Yellow
101 to 150 Unhealthy for Sensitive Groups Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon

The weather types, health effects, and recommended actions regarding the AQI levels is compiled in this table:

Air Quality Weather Conditions Recommended Actions Health Effects
AQI: 0-50
Cool summer temperatures
Windy conditions
Significant cloud cover
Heavy or steady precipitation
Keep cars and boats tuned up
Use environmentally safe paints and cleaners
Conserve electricity -- set A/C on highest comfortable level
No Health Effects are expected
AQI: 51-100
Temperatures in the upper 70s to lower 80s
Light to moderate winds
Partly cloudy or mostly sunny skies
Chance of rain or afternoon thunderstorms
Same as above Unusually sensitive people should consider limiting prolongue outdoor exertion
Unhealthy for Sensitive Groups
AQI: 101-150
Temperatures in the 80s and 90s
Light winds
Mostly sunny skies
Slight chance of afternoon thunderstorms
Limit daytime driving
Limit vehicle idling
Refuel vehicles after dusk
Do not "top off" gas tank
Avoid congested periods
Use water-based paints
Use public transit or carpool
Bike or walk short trips
Use newest/best maintained car
Combine trips and share rides
Postpone using gasoline mowers
Barbecue without starter fluid
Active children and adults, and people with respiratory disease, such as asthma, should limit prolongued outdoor exertion
AQI: 151-200
Hot, hazy, and humid
Stagnant air
Sunny skies
Little chance of precipitation
Same as above Same as above; everyone else, especially children, should limit prolongued outdoor exertion
Very Unhealthy
AQI: 201-300
Hot and very hazy
Extremely stagnant air
Sunny skies
No precipitation
Same as above Same as above

The EPA uses the AQI for five major air pollutants: carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), ground-level ozone (O3), and particulate matter smaller than 10 microns (PM10). The EPA has established national air quality standards for these pollutants, and generally pollution index values below 100 are considered satisfactory. The AQI for these pollutants, as well as the causes and health risks of these pollutants, is given below (all courtesy of the United States EPA). Also shown are data about these pollutants in six of North Carolina's cities (Asheville, Winston-Salem, Charlotte, Raleigh, Fayetteville, and Wilmington). The several top AQI values for each pollutant for each year for these cities were averaged to give a general idea of the quality of that city's air for each particular year (as mentioned earlier, usually just applies to summer air, when air quality is worst). Note that some pollutants are not measured at some locations. If there is data on a certain pollutant from a certain city, the AQI of that pollutant is indicated by the proper AQI color on the map at that location.

Carbon Monoxide

Index Values Levels of Health Concern Cautionary Statements
0 to 50
Good None
51 to 100
Moderate None
101 to 150
Unhealthy for Sensitive Groups People with cardiovascular disease, such as angina, should limit heavy exertion and avoid sources of CO, such as heavy traffic.
151 to 200
Unhealthy Same as above
201 to 300
Very Unhealthy Same as above
301 to 500
Hazardous Same as above

*ppm = parts per million

CO Map

Carbon monoxide (CO) is an odorless, colorless gas. It forms when the carbon in fuels does not completely burn. Vehicle exhaust contributes roughly 60 percent of all carbon monoxide emissions nationwide, and up to 95 percent in cities. Other sources include fuel combustion in industrial processes and natural sources such as wildfires. Carbon monoxide concentrations typically are highest during cold weather, because cold temperatures make combustion less complete and cause inversions that trap pollutants low to the ground.

What are the health effects and who is most at risk?

Carbon monoxide enters the bloodstream through the lungs and binds chemically to hemoglobin, the substance in blood that carries oxygen to cells. In this way, carbon monoxide reduces the amount of oxygen reaching the body's organs and tissues. People with cardiovascular disease, such as angina, are most at risk from carbon monoxide. These individuals may experience chest pain and more cardiovascular symptoms if they are exposed to carbon monoxide, particularly while exercising. People with marginal or compromised cardiovascular and respiratory systems (for example, individuals with congestive heart failure, cerebrovascular disease, anemia, chronic obstructive lung disease), and possibly fetuses and young infants, may also be at greater risk from carbon monoxide pollution. In healthy individuals, exposure to higher levels of carbon monoxide can affect mental alertness and vision.

Sulfur Dioxide

Index Values Levels of Health Concern Cautionary Statements
0 to 50
Good None
51 to 100
Moderate None
101 to 150
Unhealthy for Sensitive Groups People with asthma should consider limiting outdoor exertion
151 to 200
Unhealthy Children, asthmatics, and people with heart or lung disease should limit outdoor exertion
201 to 300
Very Unhealthy Same as above; everyone else should limit outdoor exertion
301 to 500
Hazardous Same as above

*ppm = parts per million

SO2 Map

Sulfur dioxide (SO2), a colorless, reactive gas, is produced during the burning of sulfur-containing fuels such as coal and oil, during metal smelting, and by other industrial processes. Major sources include power plants and industrial boilers. Generally, the highest concentrations of sulfur dioxide are found near large industrial sources.

What are the health effects and who is most at risk?

Children and adults with asthma who are active outdoors are most vulnerable to the health effects of sulfur dioxide. The primary effect they experience, even with brief exposure, is a narrowing of the airways (called bronchoconstriction), which may cause symptoms such as wheezing, chest tightness, and shortness of breath. Symptoms increase as sulfur dioxide concentrations and/or breathing rates increase. When exposure ceases, lung function typically returns to normal within an hour. At very high levels, sulfur dioxide may cause wheezing, chest tightness, and shortness of breath in people who do not have asthma. Long-term exposure to both sulfur dioxide and fine particles can cause respiratory illness, alter the lung's defense mechanisms, and aggravate existing cardiovascular disease. People who may be most susceptible to these effects include individuals with cardiovascular disease or chronic lung disease, as well as children and the elderly.

Nitrogen Dioxide

Index Values Levels of Health Concern Cautionary Statements
0 to 50
Good None
51 to 100
Moderate None
101 to 150
Unhealthy for Sensitive Groups None
151 to 200
Unhealthy None
201 to 300
Very Unhealthy Children and people with respiratory disease, such as asthma, should limit heavy outdoor exertion
301 to 500
Hazardous Children and people with respiratory disease, such as asthma, should limit moderate or heavy outdoor exertion

*ppm = parts per million

NO2 Map

Nitrogen dioxide (NO2) is a reddish brown, highly reactive gas formed when another pollutant (nitric oxide) combines with oxygen in the atmosphere. Once it has formed, nitrogen dioxide reacts with other pollutants (volatile organic compounds). Eventually these reactions result in the formation of ground-level ozone. Major sources include automobiles and power plants.

What are the health effects and who is most at risk?

In children and adults with respiratory disease, such as asthma, nitrogen dioxide can cause respiratory symptoms such as coughing, wheezing, and shortness of breath. Even short exposures to nitrogen dioxide affect lung function. In children, short-term exposure can increase the risk of respiratory illness. Animal studies suggest that long-term exposure to nitrogen dioxide may increase susceptibility to respiratory infection and may cause permanent structural changes in the lungs.

Ground-Level Ozone

Category AQI Value 1997 8-hour
2008 8-hour
Cautionary Statements
Good 0 to 50 0.000-0.064 0.000-0.059 None
Moderate 51 to 100 0.065-0.084 0.060-0.075 Unusually sensitive people should consider limiting prolonged outdoor exertion.
Unhealthy for Sensitive Groups 101 to 150 0.085-0.104 0.076-0.095 Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.
Unhealthy 151 to 200 0.105-0.124 0.096-0.115 Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged exertion.
Very Unhealthy 201 to 300 0.125-0.374 0.116-0.374 Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit prolonged exertion.
Hazardous 301 to 400 No change No change Everyone should avoid all outdoor exertion.
401 to 500 No change No change

*ppm = parts per million

O3 Map

In the Earth's lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Ozone at ground level is a harmful pollutant. Ozone pollution is a concern during the summer months, when the weather conditions needed to form it - lots of sun, hot temperatures - normally occur.

What are the health effects and who is most at risk?

Roughly one out of every three people in the United States is at a higher risk of experiencing ozone-related health effects. Sensitive people include children and adults who are active outdoors, people with respiratory disease, such as asthma, and people with unusual sensitivity to ozone. One group at high risk from ozone exposure is active children because this group often spends a large part of the summer playing outdoors. However, people of all ages who are active outdoors are at increased risk because, during physical activity, ozone penetrates deeper into the parts of the lungs that are more vulnerable to injury. People with respiratory diseases that make their lungs more vulnerable to ozone may experience health effects earlier and at lower ozone levels than less sensitive individuals. Though scientists don't yet know why, some healthy people experience health effects at more moderate levels of outdoor exertion or at lower ozone levels than the average person. Ozone can irritate the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest. Ozone can reduce lung function and make it more difficult to breathe deeply and vigorously. Breathing may become more rapid and shallow than normal. This reduction in lung function may limit a person's ability to engage in vigorous outdoor activities. Ozone can aggravate asthma. When ozone levels are high more people with asthma have attacks that require a doctor's attention or the use of additional medication. One reason this happens is that ozone makes people more sensitive to allergens, the most common triggers of asthma attacks. Ozone can increase susceptibility to respiratory infections. Ozone can inflame and damage the lining of the lungs. Within a few days, the damaged cells are shed and replaced - much like the skin peels after a sunburn. Animal studies suggest that if this type of inflammation happens repeatedly over a long time period (months, years, a lifetime), lung tissue may become permanently scarred, resulting in less lung elasticity, permanent loss of lung function, and a lower quality of life.

The maps below refer to "average fourth high value" -- this refers to the fourth highest 8-hour ozone concentration measured in a given year. Then these values are averaged for the given range of years and the counties that have an average value higher than 0.085 parts per million are indicated on the map.

Ozone 94-96
Ozone 95-97
Ozone 96-98
Ozone 97-99
Ozone 98-00
Ozone 99-01

Particulate Matter


*ppm = parts per million

PM Map

The term “particulate matter” (PM) includes both solid particles and liquid droplets found in air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles. Sources of fine particles include all types of combustion (motor vehicles, power plants, wood burning, etc.) and some industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as “coarse.” Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.

What are the health effects and who is most at risk?

Both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Adverse health effects have been associated with exposures to PM over both short periods (such as a day) and longer periods (a year or more). When exposed to PM, people with existing heart or lung diseases—such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease—are at increased risk of premature death or admission to hospitals or emergency rooms. The elderly also are sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases. When exposed to PM, children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath. PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.

PM 99-01

Below are tables of pollutant AQIs by year for the given cities. Each number is the average of the highest AQI values measured for that year for that pollutant.


Year CO NO2 O3 PM10
1990 168.148 23.594 132.5 40.378
1991 94.63 24.375 114.682 441.881
1992 112.223 23.282 124.063 38.445
1993 67.963 17.113 140.313 37.157
1994 69.444 15.625 132.188 34.148
1995 71.667 125.344 36.727
1996 92.361 112.656 34.1
1997 56.481 140.719 45.747
1998 61.481 149.375 45.533
1999 52.593 163.906 40.7
2000 75.556 148.507 41.416
2001 45.37 133.75 39.197
2002 163.25
Avg 80.65975 137.0195 39.61908
Raleigh Pollutants


Year CO SO2 NO2 O3 PM10
1990 123.222 22.5 139.063 48.539
1991 125.111 26.4 114.063 57.345
1992 131 23.126 129.063 40.596
1993 97.963 19.688 158.125 45.103
1994 87.222 48.572 17.969 132.188 45.103
1995 81.852 39.286 20.469 142.813 41.667
1996 84.722 71.072 20.001 154.688 43.287
1997 82.5 67.857 81.875 149.688 48.611
1998 72.778 58.215 20.625 157.188 47.609
1999 60.889 50 20.938 154.375 46.929
2000 83.148 62.5 28.438 139.063 47.358
2001 76.389 95.715 22.344 145.625 43.027
2002 183.25
Avg 92.233 61.65213 27.03108 146.0917 46.2645
Charlotte Pollutants


Year CO SO2 NO2 O3 PM10
1990 101.852 83.214 22.188 46.962
1991 90.741 112.5 21.407 55.144
1992 80.139 54.643 22.813 42.311
1993 58.889 152.5 24.063 128.125 45.103
1994 61.389 58.929 17.5 122.813 39.648
1995 64.861 78.929 24.375 150.156 49.13
1996 53.056 81.072 20.463 127.5 37.629
1997 60.278 64.286 20.782 136.875 47.519
1998 49.444 98.929 21.719 149.375 45.962
1999 42.407 55.357 23.282 145.625 38.159
2000 46.852 58.572 25.157 128.438 48.325
2001 42.5 95.715 20.619 132.5 52.513
Avg 62.70067 82.88717 22.03067 135.7119 45.70042
Winston-Salem Pollutants


Year O3 PM10
1990 112.823 42.096
1991 100 43.385
1992 102.5 35.233
1993 103.75 47.358
1994 105 48.325
1995 107.5 43.277
1996 104.063 44.351
1997 110 38.982
1998 143.75 41.667
1999 126.563 35.438
2000 132.188 34.579
2001 112.813 48.11
Avg 113.4125 41.90008
Asheville Pollutants


Year CO SO2 O3 PM10
1990 118.438 59.708
1991 42.526
1992 125.313 40.808
1993 36.942
1994 125.313 26.095
1995 194.943 30.713
1996 177.858 114.375 38.015
1997 118.572 124.688 33.505
1998 63.889 226.786 123.75 33.076
1999 92.778 181.072 99.375 23.948
2000 76.111 61.429 120.938 31.787
2001 73.889 112.857 113.125 24.699
2002 104
Avg 76.66675 153.3596 116.9315 35.15183
Wilmington Pollutants


Year CO SO2 NO2 O3 PM10
1990 120.556 24.286 117.188 125.938 47.68
1991 115.556 123.75 43.385
1992 128.889 118.438 39.734
1993 92.223 20.357 145 44.244
1994 103.334 18.929 121.25 39.519
1995 81.667 123.438 33.72
1996 81.667 37.857 121.563 39.948
1997 85.556 123.75 41.881
1998 65.556 140.625 41.022
1999 65.556 146.25 36.19
2000 77.222 127.188 45.461
2001 57.778 130 32.431
2002 142.5
Avg 89.63 129.9762 40.43458
Fayetteville Pollutants