About 100 million people in North America are under air quality alerts today as a thick blanket of smoke descends on cities from the upper Midwest to northeastern states. Overnight, air quality readings reached “hazardous” levels in cities including Minneapolis, Detroit and Toronto. Forecasters warn New York and many East Coast cities will spend another day under hazy orange skies. More than 1,000 active fires are burning in Canada, and dozens more in Minnesota. Meanwhile, more than 100 million people from the Plains to the East Coast face heat advisories or extreme heat warnings today, with a massive heat dome bringing triple-digit heat and record temperatures to many areas.