The US and Canada saw dangerous smoke this week. It's a routine peril for many developing countries

Thick, smoky air from Canadian wildfires made for days of misery in New York City and across the U.S. Northeast this week. But for much of the rest of the world, breathing dangerously polluted air is an inescapable fact of life — and death.

Almost the entire world breathes air that exceeds the World Health Organization’s air-quality limits at least occasionally. The danger grows worse when that bad air is more persistent than the nightmarish shroud that hit the U.S. — usually in developing or newly industrialized nations. That’s where most of the 4.2 million deaths blamed on outdoor air pollution occurred in 2019, the UN’s health agency reported.

“Air pollution has no boundaries, and it is high time everyone comes together to fight it,” said Bhavreen Kandhari, the co-founder of Warrior Moms in India, a network of mothers pushing for clean air and climate action in a nation with some of the world’s consistently worst air. “What we are seeing in the U.S. should shake us all.”