The Department of Environmental Protection has issued an ozone air quality alert for much of Pennsylvania.
The DEP says the code orange alert is in effect Thursday for the Philadelphia, Lehigh Valley, Pittsburgh, Liberty-Clairton and Susquehanna Valley areas. Under the system green represents good air quality, yellow is moderate, orange represents unhealthy pollution levels for sensitive people, and red warns of unhealthy pollution levels for everyone.
Ground-level ozone, a key component of smog, forms during warm weather when pollution from vehicles, industry, households and power plants heats up, making it hard for some people to breathe.
DEP says the elderly and those with respiratory problems such as asthma are especially vulnerable to air pollution and should limit outdoor activities.
The DEP suggest that people limit pollution-producing activities like leaving the engine idling. They also suggested that residents carpool, ride the bus and/or combine trips.