STORY: Hazy skies blanketed parts of the northeastern United States on Wednesday and the air carried the smell and bitter taste of smoke from Canadian wildfires.
Health officials issued air-quality alerts in more than a dozen U.S. states.
Authorities from Vermont down to South Carolina, and as far west as Ohio and Kansas warned that fine matter in the atmosphere could exceed unhealthy levels and make breathing difficult for millions of residents.
"This is not the time to be playing tennis or jogging or getting ready for a marathon."
Jack Caravanos is a clinical professor at New York University's School of Global Public Health.
"So, the air quality index that everybody is quoting is comprised of some priority pollutants that EPA has been regulating for years. And the one that's dominating the index today is particulate matter... The key here is there's a lot of it and it's continuous. So it's not just one little inhalation of a smoke. It's a continuous exposure. And our bodies are not good at catching those very small particles. They go right through our nose, right into our respiratory system, and we'll be impacted.”
New York City's skyline was washed a dull grey.
"We had dangerously high levels of wildfire smoke from thousands of miles away. [Flash] This is an unprecedented event in our city and New Yorkers must take precaution."
Mayor Eric Adams urged residents stay inside, wear masks outdoors, and said the city's schools remained open but that outdoor activities were being canceled, postponed, or moved inside.
"This is a moving situation, and we will keep New Yorkers informed on any changes based on updated air quality conditions.''
The smoke is crossing the U.S. northern border from Canada, where the wildfire season got off to an unusually early and intense start due to persistent warm and dry conditions.
Canada is on track for its worst-ever wildfire season.
"We're seeing people across the country being affected. We're seeing vulnerable people at risk. Outdoor events cancelled. Kids having to be kept inside at recess."
Canadian Prime Minister Justin Trudeau on Wednesday thanked the country's firefighters battling the blazes and urged citizens to heed health warnings.
"Please, listen to your local health agencies, about how to stay safe."
There are blazes in nearly all of Canada's provinces and territories, with Quebec the worst affected.
Multiple fires were touched off by lightning strikes.
The air quality in Canada's capital city of Ottawa, remained in category 10+, which Canada's Air Quality Health Index said was "very high risk."