The Pennsylvania Department of Environmental Protection has issued a Code Orange Air Quality Action Day for fine particulate matter for Monday in the counties of Bucks, Chester, Delaware, Montgomery, and Philadelphia in southeastern Pennsylvania, the counties of Berks, Lehigh, and Northampton in the Lehigh Valley-Berks area.

A strong ridge of high pressure will remain over Pennsylvania through Monday. Strong morning temperature inversions and weak winds will contribute to concentrations of fine particulate matter in the Code Orange range. The highest concentrations are most likely to occur between 3 a.m. and 10 a.m. Concentrations may decrease during the afternoon, but not enough to keep daily average concentrations below the Code Orange range.

The U.S. Environmental Protection Agency’s Air Quality Index provides standardized color codes for forecasting and reporting daily air quality. Green signifies good air quality; yellow means moderate air quality; orange represents unhealthy pollution levels for sensitive groups of people; and red warns of unhealthy pollution levels for all.

An Air Quality Action Day is issued when the AQI is forecasted to be code orange or higher. On air quality action days, young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should limit outdoor activities.