Canada is currently experiencing its worst wildfire season ever, and on Monday smoke from the hundreds of blazes once again drifted across the border into the United States, prompting another round of air quality warnings.

The new bout of smoke and haze led to air quality alerts being issued for around 70 million people in 32 states and the District of Columbia, from Montana across to Vermont and all the way down into Northern Alabama, reported CNN and The New York Times. Cities affected included New York, Cleveland and Chicago.

“We are acutely aware that the recent weather events prominently impacting our City this summer are the direct result of the climate crisis,” said Chicago Mayor Brandon Johnson, as The New York Times reported.

Precautions like wearing masks and limiting time outside were recommended by officials. Wildfire smoke can irritate the nose, throat and eyes, and can lead to breathing issues. Exposure has also been associated with increased risks of heart attack, lung cancer, stroke and cognitive decline.

“The advice to limit strenuous activities is because when your respiratory rate is higher, you inhale more particulates,” said Yale Medicine’s Dr. Carrie Redlich on the Yale Medicine website. The tiny particles from the smoke “get everywhere through the bloodstream and trigger inflammatory pathways, which can exacerbate a number of underlying cardiac and respiratory conditions.”

Redlich said the best kind of mask to wear to protect yourself from the poor air quality that comes with wildfire smoke is an N95 or P100.

Read the full article about wildfire smoke by Cristen Hemingway Jaynes at EcoWatch.