People hundreds of miles away can be negatively affected by the hazardous microscopic particles they produce, which can trigger inflammation in the lungs when inhaled and can worsen medical conditions like asthma and heart disease.
Why millions in the U.S. are experiencing dangerous air quality levels
Wildfire smoke from Yukon to Nova Scotia is engulfing northeastern U.S. and Canada, choking major cities like New York and Toronto with hazardous air quality.
Threat level
Smoke, and other forms of air pollution, drifted over Tuesday and many cities saw among the worst air quality in the world overnight.
Air quality advisories were affecting up to 100 million people across the U.S., from the Northeast to the Midwest and Texas.
Driving the news
N.Y.C. Mayor Eric Adams issued a statement urging all New Yorkers to limit outdoor activity to the greatest extent possible.
Plumes of smoke from wildfires scorching southeastern Canada's Nova Scotia province are drifting across the Northeastern U.S. and prompting air quality alerts in several cities.
Go Deeper
Here's how wildfire smoke and air quality levels affect your health.