The region's sizzling temperatures are causing more than just general discomfort. It's also affecting air quality. Southeastern Pennsylvania, New Jersey and Delaware are under an orange ozone alert.
Heat alone doesn't cause air problems, but it's a big factor around Philadelphia, according to Eric Cheung, deputy director of the Clean Air Council.
"Our region tends to produce a lot of the precursor pollutants that lead to ozone and smog," said Cheung. "And on hot, sunny days those pollutants mix together and form the ozone or smog."
Area power plants, refineries and transportation activity are major sources of this. David Fees, a manager with the Delaware Department of Natural Resources, says the alert means seniors, young kids, people with asthma are at greater risk for respiratory problems.
"Ozone, when breathed in, is a lung irritant," said Fees. "And it will cause shortness of breath and tightness in the chest and difficulty with breathing"
Fees says the best thing to do is stay indoors. To avoid adding to the pollution, fuel vehicles in the morning or evening, before the heat reaches its peak.
So far, the region has experienced six orange alerts this year. According to Fees and Cheung, rain and mild temperatures have kept ozone levels down until now.