- Introduction [1]
- Air Quality Index [2]
- Carbon Monoxide [3]
- Sulfur Dioxide [4]
- Nitrogen Dioxide [5]
- Ground-Level Ozone [6]
- Particulate Matter [7]
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.
The Environmental Protection Agency [8] 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 |
| Good AQI: 0-50 (Green) |
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 |
| Moderate AQI: 51-100 (Yellow) |
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 (Orange) |
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 |
| Unhealthy AQI: 151-200 (Red) |
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 (Purple) |
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.
| Index Values | Levels of Health Concern | Cautionary Statements |
| 0 to 50 (0-4.5ppm) |
Good | None |
| 51 to 100 (4.5-9ppm) |
Moderate | None |
| 101 to 150 (9-13.5ppm) |
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 (13.5-18ppm) |
Unhealthy | Same as above |
| 201 to 300 (18-27ppm) |
Very Unhealthy | Same as above |
| 301 to 500 (27-45ppm) |
Hazardous | Same as above |
*ppm = parts per million
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.
| Index Values | Levels of Health Concern | Cautionary Statements |
| 0 to 50 (0-0.07ppm) |
Good | None |
| 51 to 100 (0.07-0.14ppm) |
Moderate | None |
| 101 to 150 (0.14-0.21ppm) |
Unhealthy for Sensitive Groups | People with asthma should consider limiting outdoor exertion |
| 151 to 200 (0.21-0.28ppm) |
Unhealthy | Children, asthmatics, and people with heart or lung disease should limit outdoor exertion |
| 201 to 300 (0.28-0.42ppm) |
Very Unhealthy | Same as above; everyone else should limit outdoor exertion |
| 301 to 500 (0.42-0.70ppm) |
Hazardous | Same as above |
*ppm = parts per million
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.
| Index Values | Levels of Health Concern | Cautionary Statements |
| 0 to 50 (0-0.16ppm) |
Good | None |
| 51 to 100 (0.16-0.32ppm) |
Moderate | None |
| 101 to 150 (0.32-0.48ppm) |
Unhealthy for Sensitive Groups | None |
| 151 to 200 (0.48-0.64ppm) |
Unhealthy | None |
| 201 to 300 (0.64-0.97ppm) |
Very Unhealthy | Children and people with respiratory disease, such as asthma, should limit heavy outdoor exertion |
| 301 to 500 (0.97-1.62ppm) |
Hazardous | Children and people with respiratory disease, such as asthma, should limit moderate or heavy outdoor exertion |
*ppm = parts per million
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.
| Category | AQI Value | 1997 8-hour (ppm) |
2008 8-hour (ppm) |
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
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.
*ppm = parts per million
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.
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.
Raleigh
| 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 |
Charlotte
| 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 |
Winston-Salem
| 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 |
Asheville
| 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 |
Wilmington
| 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 |
Fayetteville
| 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 |
