COLUMBIA, S.C. — The South Carolina Department of Health and Environmental Control has declared Wednesday as a code orange air quality action day. The air quality alert is in effect until 8 pm Wednesday and includes Calhoun, Fairfield, Kershaw, Lexington, Newberry, Richland, Saluda and Sumter counties.

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Atmospheric conditions are expected to produce unhealthy concentrations of ground level ozone today. Ozone is a compound made of three molecules of oxygen, which is an irritant to people, animals, and even plants. Today's ground level ozone may reach levels that can impact sensitive groups including children, elderly, and people with heart or lung disease.

Ozone is created when pollution and naturally occurring elements (like oxides of nitrogen) combine with heat. Today's hot and calm weather is perfect for this reaction. Ozone forms faster when the air is very hot and high pressure acts like a lid, keeping the ground ozone from dispersing.

Not all ozone is made the same. Ground level ozone is an unnaturally occurring pollutant, but higher in the atmosphere, ozone occurs naturally and shields Earth from dangerous solar radiation. That's why the Environmental Protection Agency claims ozone is "good up high, bad nearby".

Sensitive groups should reduce prolonged or heavy outdoor exertion, take more breaks and do less intense activities, especially during the afternoon and early evening hours.

Drivers can help reduce ozone pollution by carpooling, walking or riding a bicycle, taking lunch to work, reducing idling in your car, and keeping your vehicle properly tuned.

Concentrations of ground level ozone will improve a few hours after sunset and with rain in the forecast tomorrow, the air quality will improve on Thursday.