Code Orange air quality alert in effect Monday for central, eastern Pa. Updated Dec 20, 2020; The Pennsylvania Department of Environmental Protection (DEP) has issued a Code Orange Air Quality Action Day for fine particulate matter for Monday in the southeastern counties of Bucks, Chester, Delaware, Montgomery, and Philadelphia; the southcentral counties of Cumberland, Dauphin, Lancaster, Lebanon, and York; and the Lehigh Valley-Berks Area which includes the counties of Berks, Lehigh, and Northampton. A strong temperature inversion supported by snow cover, along with light winds associated with high pressure, are likely to contribute to daily average concentrations of fine particulate matter in the Code Orange range, according to a press release sent out Sunday afternoon.