NYC ranked first among major cities for the worst air quality worldwide today, according to IQAir, a Swiss air monitoring company.

The smoke from ferocious Canadian wildfires cast a sickly pall over much of the eastern United States today, worsening air quality for millions of people. The air was acrid, skylines looked orange and municipal officials told people to stay indoors. The National Weather Service does not expect things will get much better tomorrow.

About 98 million people in parts of 18 states from New Hampshire to South Carolina were under air quality alerts this morning for both wildfire smoke and ozone.

“This is a historic event. We’ve gone back to our smoke data and not seen anything of the same magnitude and size on the East Coast,” Burke said. And for New York City, “it’s by far the worst in the last 18 years.”

Wednesday — once data is analyzed — could be the worst day of smoke in the U.S. in nearly two decades, Burke said.