The Pennsylvania Department of Environmental Protection has issued a "code orange" air quality alert for unhealthy particle pollution for Saturday for the entire region.
With high temperatures approaching records and light winds inhibiting the mixing of air, levels of particle pollution, a key ingredient in smog, will increase, state officials said Friday.
On such days, the very young, the elderly and those with respiratory problems should limit outdoor actitivies, the state advised.
In addition to the Saturday alerts for Philadelphia and its four neighboring Pennsylvania counties, they are in effect Sunday for Berks, Cumberland, Dauphin, Lancaster, Lebanon, Lehigh, Northampton, and York Counties.
The EPA uses a colors index to report daily air quality: Green signifies good; yellow, moderate; orange, unhealthy for sensitive people, and red, unhealthy pollution levels for all.