In early June, as toxic wildfire smoke from Canada blanketed the Northeast, Linsey Marr, Ph.D., a professor of environmental science at Virginia Tech and one of the nation’s preeminent air experts, sat at her computer, feeling agitated as she scrolled through Twitter. She couldn’t believe what she was seeing.

She’s recounting this to me in her office in Blacksburg, Virginia, a standard academic desk-and-bookshelf setup dotted with the stuff of her life: framed diplomas and a looming print of a ski slope; a well-organized desktop hosting air-measuring gadgets and an equation-filled textbook; the black Spot bike she rode to work parked in the corner. She’s describing how, just 500 miles to the north of this very place, the scene looked apocalyptic.

The next day, the air in the New York metropolitan area was so bad—the air-quality index (AQI) topped a historic 400—it turned a disturbing shade of amber. The spreading pollution tripped air-quality alerts throughout not just the Northeast but also the Midwest and Southeast. When it floated its way to her doorstep, the AQI clocked above 140, nearly at the red zone: unhealthy for everyone.