Air quality forecasts are important in determining the amount of pollutants in the air, which can affect our health. The National Ambient Air Quality Standards (NAAQS) are set by the Clean Air Act and the U.S. Environmental Protection Agency (EPA) for pollutants considered harmful to public health and the environment. In South Carolina, the Bureau of Air Quality at the South Carolina Department of Health and Environmental Control (SCDHEC) monitors the air throughout the state to measure concentrations of pollutants in the air.

These monitors are used to measure where the highest concentrations occur, when they are expected to occur, and how this can affect health and the environment. These monitors focus on six pollutants identified as the largest risks for health concerns. These are carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), lead (Pb), particulate matter (PM), and ozone (O3). The EPA sets an Air Quality Index chart (example A)1 which determines levels of pollutants in an area and the impacts those levels have on health. On the EPA website (, one can build an Air Quality Index Report (example B)2, which will show how many days out of the year pollutants were present throughout the state, broken down by county.

Carbon monoxide (CO) is a colorless, odorless gas produced when something burns incompletely. It can also be produced if something is burned in a closed-in area. This gas is toxic to all humans and animals, and can be formed from gas heaters and stoves, incorrectly vented furnaces, and automobiles idling in a closed garage. Overexposure to carbon monoxide can cause health problems such as headaches, drowsiness, dizziness, confusion, and even death.

Nitrogen dioxide (NO2) is a gaseous compound made up of nitrogen and oxygen, and is produced by burning fossil fuels such as gasoline and coal, which can come from automobiles, power plants, and coal-burning stoves. Nitrogen dioxide can cause lung disease and can aggravate an existing heart condition.

Sulfur dioxide (SO2) is a gaseous compound made up of sulfur and oxygen that is produced by burning coal and oil, which can come from power plants, coal-burning stoves and refineries. Sulfur dioxide can cause lung disease, eye irritation and burning of the skin. When NO2 and SO2 combine with water and sunlight high in the atmosphere, acid rain can form. It can fall to the ground in the form of rain or snow. This can be harmful to plant and aquatic life, can damage forests and vegetation, and can erode buildings and statues.

Lead (Pb) is a metal found in a dust-like form in the air. Lead can be found in paint in old houses, smelters used in metal refineries and contaminated soil and dust. Lead poisoning can cause brain and nervous system damage, digestive problems, kidney damage, reproductive system damage and learning disabilities in children.

Particulate matter (PM) are solid particles and liquid droplets present in the air that come from diesel engines, power plants, industrial processes, dust and wood stoves. They may be present in the form of dust, soot, pollen and smoke. Particulate matter can cause breathing problems, increased asthma, lung or heart problems in people who already have these problems, bronchitis and irritation of the nose, eyes, throat and skin. There are two types of particulate matter monitored. They are PM2.5 and PM10. PM2.5, or fine particulates, are particles with diameters less than or equal to 2.5 micrometers. PM10, or course particulates, are particles with diameters less than or equal to 10 micrometers.

Ozone (O3) is a colorless gas made up of three atoms of oxygen. It can be found in the stratosphere naturally and protects us from the ultraviolet rays of the sun. This is known as "good" ozone. Ground-level ozone can be found in the troposphere and is formed when nitrogen oxides and volatile organic compounds (VOCs) combine with sunlight. This is known as "bad" ozone. Pollutants that help form ground-level ozone include industrial air emissions, automobile exhaust, gasoline vapors, and chemical solvents. These reactions can also form smog. Ground-level ozone can inflame lungs and respiratory tissue, impair the body's immune system and can cause eye irritation.

The EPA sets standards against ozone and other pollutants. There are two sets of standards, primary and secondary. The primary standard protects health. The secondary standard protects public welfare, to include effects on the environment. On March 12, 2008, the EPA revised the NAAQS standard for ground-level ozone. The primary standard, also the 8-hour ground-level ozone standard is 0.075 parts per million (ppm) as a result of new scientific evidence of ground-level ozone and the effects on human health. The secondary standard which protects plants, trees and crops was set to 0.075 ppm also, the same as the primary standard, based on scientific evidence indicating that exposure to low levels of ozone can damage vegetation.3 Currently, SC DHEC only forecasts for ground-level ozone. Daily information about air quality, including ground-level ozone and particulate matter, and how they may affect health can be found on AIRNOW (a government website at

SC DHEC forecasts ground-level ozone to protect public health and to comply with EPA standards from May 1-September 30. The first step in forecasting ground-level ozone is to analyze the current day's meteorological conditions because this can have an effect on the current ozone. The next step is to forecast the next day's meteorological conditions. Ozone patterns tend to follow weather patterns so it's important to know the weather patterns. Some things to consider when forecasting weather patterns are to look at current meteorological conditions, surface, upper-air, and atmospheric profiles, satellite and radar images, climatological data, and interpret forecast model data. The next step would be to look at ambient ozone monitoring. An air dispersion model is produced. SC DHEC defines an air dispersion model as a set of mathematical equations that relate the release of air pollutants from emission sources to the corresponding concentration of pollutants in the ambient air. The ozone models use actual emissions values (from industry, automobiles, etc.) to determine the actual monitor values. Certain meteorological and non-meteorological variables need to be present for high ozone. Meteorological variables include a ridge present with vertical stability, hot surface temperatures, dry air, stagnant wind speed coming from the west, southwest, or northeast, little or no cloud cover, recirculation of precursors, and dry soil. The most important of these variables are hot temperatures, dry air, and stagnant wind. Non-meteorological variables include a high ozone peak on the previous day, high current ozone levels, and high sun angles. The ozone values from the models are then compared to EPA's Air Quality Index Chart (example A), and a forecast is issued. The forecast is then distributed to the EPA, which is then redistributed to the National Weather Service, TV and radio, and The Weather Channel. For the state of South Carolina, this forecast can be found at If the ozone is high enough to reach unhealthy levels, an Air Quality Action Day may be declared. This informs the public to take precautionary measures to protect themselves against ground-level ozone.

Forecasting air quality in South Carolina can be difficult for several reasons. Because South Carolina is on the coast, coastal climatology needs to be considered. Pollutants produced on the coast can get trapped in stable air as it moves onshore, which increases local concentrations. Understanding the geography and the timing of sea breeze events as well as pollution emissions would help a great deal to ensure an accurate forecast. Another issue that makes forecasting difficult is when an exceptional event occurs. According to the EPA, and exceptional event is one that affects air quality, is not reasonably controllable or preventable, caused by human activity that is unlikely to recur at a particular location, or is a natural event, and determined by the Administrator of the EPA through the process established in the rule to be an exceptional event. On March 29, 2007, the Congaree Bluff air monitoring site (45-079-0021), operated by the Bureau of Air Quality, SC DHEC, within Congaree National Park near Gadsden, South Carolina, experienced increased ozone levels which exceeded standards due to a prescribed fire burn. From approximately 10:45-11:01 a.m. EST, ozone concentration peaked at 237 ppb. The maximum 8-hr average for the day was 91 ppb, which exceeded the National Ambient Air Quality Standard for ozone. Other areas were at or below 48 ppb, which is typical for the season and region.4 When exceptional events such as this happen, it can throw the forecast off.

Air quality forecasts can be very helpful to the public to maintain a healthy life. The forecasts must be accurate, which means the models and data going into the models must also be accurate. The forecasts must also be released in a timely manner because the information is not helpful if it is received too late. With this in mind, air quality forecasts can be very beneficial to human health and the environment.


1 U.S. Environmental Protection Agency, (2008), Retrieved March 29, 2008, Air Quality Index, from
2 U.S. Environmental Protection Agency, (2007), Retrieved March 29, 2008, Air Quality Index Report, from
3 South Carolina Department of Health and Environmental Control, (2008), Retrieved March 29, 2008,
New Ground Level Ozone Standard, from
4 Hulslander, Bill, Congaree National Park, (2007, March 29), Retrieved from South Carolina
Department of Health and Environmental Control, March 29, 2008,
Congaree Bluff Air Monitoring Site Ozone Exceedance March 29, 2007, from