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The dirtiest air in the world

The US slashed air pollution over the past 60 years. But on Thursday, US cities suffered some of the world’s worst air.

This story appeared in Today, Explained, a daily newsletter that helps you understand the most compelling news and stories of the day. Subscribe here.

Canadian wildfire smoke is pouring over the US border today, blanketing much of the Northeast and Upper Midwest in fine particulate.

When I went outside to water plants in Buffalo this morning, the air tasted like campfire and glowed with a faint amber haze. My colleague Zack Beauchamp, who lives in Ontario, said “the sky looked genuinely apocalyptic” in Toronto yesterday.

The heavy smoke comes from both the hundreds of wildfires raging across Canada and a meteorological phenomenon known as a “heat dome,” which traps hot,........

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