The smoky scenes and threat of fast-moving fires ― so common in California during recent summers ― are now paying the eastern United States an unwelcome, improbable and toxic visit.

A thick veil of Canadian wildfire smoke is spreading south over much of the Midwest, Ohio Valley, Northeast and Mid-Atlantic, bringing milky-white skies and dangerous air pollution to the most populous corridor of the country. Fine particles contained within the smoke, hazardous to breathe, have prompted air quality alerts for tens of millions of people from Baltimore to Boston to Burlington, but measurements show bad air affecting even a larger area that includes Minneapolis and Washington, D.C.

In some places, air quality measurements are the worst on record.

As of midmorning Tuesday, New York City, Detroit and Toronto were ranked among the 15 cities with the worst air quality in the world.

― Washington Post