Officials are warning Philadelphia-area residents about poor air quality in the region Thursday.
Some parts of the area, including Philadelphia and many Pennsylvania suburbs, are under a "code red" air quality alert, which means pollution levels are unhealthy for the general population.
A less-severe "code orange" alert has been issued for other places in the area, including South Jersey. That means pollution levels may be dangerous for sensitive groups like children, the elderly and people with asthma, heart disease or lung conditions.
Ozone levels across the area are "rising much faster than expected" due to "warm and sunny conditions, a polluted regional air mass, and the contribution of diluted smoke transported from wildfires in Canada," according to AirNow.gov, the federal air-quality website.
High ozone levels are also expected Friday. Both days are also expected to be warm, with temperatures reaching about 90 degrees.