HARRISBURG, Pa. (CBS) - Today and tomorrow are “orange alert” days for air quality in southeastern Pennsylvania.

Code orange is two steps above green, which is “good” air quality. Yellow is moderate. Orange means unhealthy pollution levels for sensitive people. Next would be red, which is unhealthy air for all.

Late this afternoon, the Pennsylvania Department of Environmental Protection extended the alert for Philadelphia and surrounding counties another day, and expanded the area to include Lehigh County.

“We want to make sure that certain populations are staying indoors, staying in cool areas,” says Katie Gresh, a spokeswoman for the Pennsylvania Department of Environmental Protection.  “If they are outdoors that they are in the shade, that everyone has cold water on them when they are outside.”

Among the sensitive populations of particular concern are young children, the elderly, and those with respiratory problems like asthma, emphysema, and bronchitis.

The heat affects the air quality when the sun “bakes” the pollution to form more ground-level ozone, a key component of smog.

Reported by KYW Harrisburg bureau chief Tony Romeo