The Pennsylvania Department of Environmental Protection has forecast Friday to be an orange air quality action day for ozone in the Philadelphia area, after the department issued the same warning for Thursday as well.
Ground-level ozone, a component of smog, forms when pollution from cars, households, manufacturing and power plants combine in the warm weather and "bake" in the sun, according to a DEP release.
The DEP uses the U.S. Environmental Protection Agency's standardized air quality index to daily code conditions as green, which means conditions are good; yellow, which signifies moderate pollution; orange, which represents unhealthy pollution for vulnerable people; and red, which signifies unhealthy levels of pollution for all people.
On orange air quality action days such as Thursday and Friday, young children, the elderly and those with respiratory problems like asthma, emphysema and bronchitis are advised to limit outdoor activities.
The DEP is further encouraging residents and businesses to do their part in voluntarily limiting pollution by limiting engine idling, refueling cars and trucks after dusk and conserving energy in homes and businesses.
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Also contributing to the state forecasts are the Air Quality Partnership of the Delaware Valley, the Southwest Pennsylvania Air Quality Partnership, the Lehigh Valley-Berks Air Quality Partnership and the Susquehanna Valley Air Quality Partnership.