In early June, the sky turned yellow throughout much of the northeastern United States. People woke up to smog, haze, and a red sun, and were warned to stay indoors to protect themselves from a toxic cocktail of air pollutants. In New York City, the levels of particulate matter with 2.5 microns or less in size (PM2.5) were registered at a record-breaking 400 micrograms per cubic meter. This reading exceeded the U.S. Environmental Protection Agency’s recommended 24-hour standard guidelines 11 times and was equivalent to every person in the city, including babies, smoking 5-10 cigarettes. Such unprecedented levels of air pollution made New York the most polluted of all big cities in the world on that day, displacing perennial record holders like New Delhi or Lahore.

The bad air in New York City and across the Northeast was carried by winds from Alberta, Nova Scotia, and Quebec – Canadian provinces experiencing record-high temperatures and droughts that have caused an unprecedented number of wildfires.

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