What's in the Air.

The air over rapidly growing city areas such as Charlotte and the Triangle area contains pollution from two major sources: automobiles and industries. From these sources come two major forms of pollution: ozone and carbon monoxide.

The word "ozone" confuses most people because it seems to have several definitions--as something that protects us from sunburn and as bad air that we should avoid breathing` on a "red code" ozone day. Actually, there are two types of ozone: good and bad. Good ozone, an odorless, colorless gas composed of three oxygen atoms, lives in Earth's upper atmosphere and forms a protective layer that shields the Earth from the sun's ultraviolet rays. The good ozone keeps people from getting sunburned but is slowly being depleted by manmade chemicals. Bad ozone, on the other hand, lives near the ground and is a cloud of pollutants emitted by power plants, industries, automobiles and other types of transportation. This ozone forms through a complex set of chemical reactions between hydrocarbons, nitrogen oxides, and sunlight. These reactions increase during periods of higher temperature and sun intensity; hence, ozone tends to be more problematic during the hot summer months and often reaches its peak in the afternoon.

Like ozone, carbon monoxide is a colorless, odorless gas, but higher concentrations of it are much more deadly. Carbon monoxide forms inside the engine of an automobile when the fuel does not burn properly and deposits remain in the fuel line. Typically, this process occurs with a low ratio of air to fuel in the engine, which happens when the vehicle is started, when it is not tuned properly, and at higher altitudes. In urban areas, 90 percent of carbon monoxide pollution originates from automobiles. Carbon monoxide levels tend to be higher during cold weather, exacerbated by idling engines to "warm up the car" and peak during rush hours: weekday mornings and afternoons.

Automobiles also produce particulate matter and nitrogen dioxide, two other toxins that affect the respiratory system.

Since air pollution consists of several compounds, its effect on our health depends largely on how much of each compound is present in the air. Most people have heard radio, TV and newspaper reports of "code red" or "code orange" days for ozone. However, the codes reported in the news for ozone aren't specifically isolating ozone levels. Instead, they measure several air pollutants combined. Where does the weather service get these codes? From an indicator for the amount of pollution in the air, the Air Quality Index (AQI). The AQI includes five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Based on standards set by the federal Clean Air Act, the AQI is an index that reports how clean or polluted the air is and what health concerns exist. The AQI spans from 0 to 500, and values below 100 are considered satisfactory, or "code green." Anything higher than that is a health risk, first for people who are especially sensitive, and then everyone else as values get higher. A "code green day" has an AQI between 0 and 50 and usually is safe for everyone, while "yellow" is acceptable for everyone except the extremely sensitive. Code Orange starts with an index of 101, and maroon is the most unhealthy, considered hazardous for everyone, with values between 301 and 500.

North Carolina sometimes has "code red" days during July and August, since they are the hottest. Most of the pollutants increase susceptibility to respiratory infections and cause coughing, sore throat, and more rapid and shallow breathing because of reduced lung function. Although sensitive people experience these effects to a great degree, people with mild allergies can suffer them as well. Therefore, during afternoon rush hour, in warmer months, people may notice what seem like cold symptoms: runny nose, tight chest and sore throat, mainly due to increased levels of air pollution.

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