Massive plumes of Canadian wildfire smoke are set to pour over the border into the United States, bringing dangerous air quality to more than 100 million people in the Midwest and Northeast. Smoke has already plagued the West, Plains and Midwest as stateside fires burned 3.6 million acres, while Canada’s own blazes have scorched nearly 4.5 million acres this summer.

In Canada, over 3,000 fires have ignited, with dozens erupting in Ontario. A record‑breaking heat dome over the central US is funneling the smoke south‑east, a pattern that mirrors last year’s 2023 event when 4,300 fires in Canada consumed 25 million acres. The high‑pressure system has trapped the soot, allowing it to linger and bring unhealthy air quality from the Upper Midwest to New England.

Wildfire smoke contains tiny PM2.5 particles that can penetrate deep into the lungs and bloodstream, provoking breathing problems, bronchitis, and aggravating heart and diabetes conditions. Michigan, Minnesota, and Wisconsin are under air‑quality alerts; the National Weather Service warns that Chicago could see worsening conditions later this week. Residents with lung or heart disease, children, and older adults are especially at risk.

Climate‑driven heat domes and rising fossil‑fuel pollution are extending wildfire seasons, eroding decades of air‑quality gains and contributing to an estimated 15,000 excess deaths in the US from 2006‑2020, a recent study found.