But those with asthma and breathing problems say the poor air quality has been in the area for much longer, and it's compounding an already difficult spring.
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"Pollen plus pollution and smoke particulate just makes a bad situation worse," said Dr. Manav Segal, of Chestnut Hill Allergy and Asthma.
Dr. Segal said the Air Quality Index (AQI) has shown increased particulates for weeks and his patients have been calling for help.
SEE ALSO: Hazardous smoke from Canada wildfires hangs over Philadelphia, Delaware Valley
"Really early on it was my own patients tipping me off to the environmental changes they were experiencing," said Dr. Segal.
On Thursday, city officials in Philadelphia asked people to stay indoors with the windows closed. They recommend wearing a mask outside because the particulates from the smoke can cause problems for anyone who breathes them in.
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"The fine particles can penetrate deeply into fragile lung tissues, causing symptoms of cough, shortness of breath and wheezing," said Dr. Cheryl Bettigole, Philadelphia's health commissioner.
The message seemed to be getting out. More people were seen wearing masks in Rittenhouse Square on Thursday afternoon.
SEE ALSO: Why is smoke from Canada impacting the Philadelphia region and when will it go away?
Action News checked with emergency rooms across the region, and none reported a significant uptick in patients with breathing problems.
Dr. Segal is hearing from his patients, though. He likened what the Northeast is seeing to the AQI in the Pacific Northwest during wildfire season.
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"I've never seen anything like this where the air quality has been this poor," said Dr. Segal.
SEE ALSO: Why smoke from wildfires could cause a host of symptoms - even in healthy people
6abc Air Quality Tracker