(Bloomberg) -- The worst Canadian wildfire season in recorded history spread an orange haze from Massachusetts to South Carolina and as far west as Missouri, threatening to disrupt flights and forcing millions to mask up or stay inside. 

Philadelphia and Baltimore registered some of the worst air quality readings in the US with the level exceeding 300 on Thursday, a number considered hazardous, according to the Environmental Protection Agency’s AirNow map. Manhattan recorded in the 200 range — but New York’s Mayor Eric Adams warned the unprecedented conditions could again deteriorate and urged people to take precautions. 

Washington, DC, was under a “Code Purple” air quality alert, indicating “very unhealthy air conditions for the entire public,” according to the office of Mayor Muriel Bowser.

“Based again on the forecast that the National Weather Service is putting out, we could see the winds that are pushing the smoke south from Canada begin to shift,” said Christopher Rodriguez, director of DC’s Homeland Security and Emergency Management Agency. “So that will ease again some of the air quality challenges that we’re facing into the weekend.”

New York City area airports including LaGuardia and Newark are facing ground delays for a second day due to low visibility. The delays could create a ripple impact on US flights as lots of air traffic flows through New York and the Northeast.

Inbound flights to New York’s LaGuardia Airport werefor a second day due to low visibility, while the Federal Aviation Administration warned that flights could also be halted at JFK, Newark and Teterboro. 

The haze is expected to last into Monday or Tuesday before the larger weather pattern pumping smoke south from Canada starts to break up, according to Zack Taylor, a senior branch forecaster with the US Weather Prediction Center. The plume itself covers most of North America and in the long term, the only real solution will be if the fires in Canada are brought under control.

For now, dystopian scenes gripped those in cities unfamiliar with this type of pollution, which is far more prevalent in Asia and increasingly affects parts of North America. Historic wildfires have blanketed large parts of Northern California in smoke in recent years and turned San Francisco’s skies orange in 2020. 

Canada is leading the world right now in the number of powerful blazes over the past 24 hours, data from NASA satellites show, with more than 400 forest fires active across the country and many of them raging out of control. Prime Minister Justin Trudeau blamed climate change for exacerbating the problem and said that hundreds of US firefighters have arrived in Canada.

President Joe Biden offered additional support to fight the blazes and New York state was distributing a million N95 masks on Thursday as officials across the region urged residents to stay inside. 

New York and the Northeast should get ready for more smoke through September as long as fires continue to burn across Quebec and eastern Canada, said Mark Wysocki, New York state’s climatologist and a lecturer at Cornell University.

“The potential is there not only for this summer but going right into the fall,” he said. “We are going to have to adapt to this.”

--With assistance from Brian K. Sullivan and Skylar Woodhouse.

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