Philly and its suburbs are under a Code Orange due to poor air quality

The Philadelphia region on Thursday is under a Code Orange Air Quality Action Day for Ozone.

The alert, issued Wednesday by the state Department of Environmental Protection, includes Bucks, Chester, Delaware, and Montgomery counties.

Also included are Berks, Lehigh, and Northampton counties in the Lehigh Valley, and Cumberland, Dauphin, Lancaster, Lebanon, and York counties in the Susquehanna Valley.

Ozone, a gas that’s harmful when breathed in, forms from a combination of heat and different pollutants.

An 8-hour average of ozone concentrations in the Code Orange range is expected, state Department of Environmental Protection officials said, citing partly to mostly sunny skies and temperatures in the mid-90s.

Under a Code Orange, air pollution concentrations may be unhealthy for vulnerable groups such as children, people with asthma, people with heart or lung disease, and older adults.

Local conditions may fall above or below Code Orange range. Residents are encouraged to visit AirNow.gov to check local conditions.