Updated:PITTSBURGH (AP) (AP)ong> - An air pollution alert is in effect for five Pennsylvania regions.
The Department of Environmental Protection said in a release that a Code Orange ozone alert is in effect Friday for the Lehigh Valley, Liberty-Clairton, Pittsburgh, the Susquehanna Valley, and Mercer County.
Young children, the elderly and those with respiratory problems such as asthma should limit outdoor activities. Ground-level ozone, or smog, forms during warm weather when pollution from vehicles, power plants and other sources heats up, making it hard for some people to breathe.
The alert system uses colors to report air quality. Green signifies good; yellow is moderate; orange means unhealthy pollution levels for sensitive people; and red warns of unhealthy pollution levels for everyone.