Why Is It So Hazy? Wildfire Smoke Brings Red Skies, Health Warnings

Smoke from blazes in the Western United States and Canada stretched across North America this week.,

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Wildfire smoke spreads haze and health warnings to East Coast.

New York City was enveloped by a cloud of haze on Tuesday. 
New York City was enveloped by a cloud of haze on Tuesday. Credit…Bryan Anselm for The New York Times
  • July 21, 2021, 11:38 a.m. ET

Wildfire smoke from Canada and the Western United States stretched across North America this week, covering skies in a thick haze, tinting the sun a malevolent red and triggering health alerts from Toronto to Philadelphia. Air quality remained in the unhealthy range across much of the East Coast on Wednesday morning.

The map below, based on modeling from the National Oceanic and Atmospheric Administration, shows how the smoke spread across the country. It reflects fine particulate pollution released by wildfires and does not include pollution from other human sources, like power plants and cars.

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It’s not unprecedented to see smoke travel such long distances, said Roisin Commane, an atmospheric scientist at Columbia University, but it doesn’t always descend to the surface.

The air quality index, a measure developed by the Environmental Protection Agency, spiked across the Midwest and East Coast this week, with numbers hovering around 130 to 160 in New York City, a range where members of sensitive groups and the general public may experience adverse health effects. (The index runs from 0 to 500; the higher the number, the greater the level of air pollution, with readings over 100 considered particularly unhealthy.)

In other East Coast cities, readings also remained elevated early Wednesday: 126 in Baltimore, 121 in Narragansett, R.I., and 129 in Pennsylvania’s Lehigh Valley.

Eerie red sun rises were recorded across the region. The pollution was forecast to begin lifting over the New York area late Wednesday morning, but the smoke was then expected to push south to Washington, D.C., and Virginia.

More than 80 large fires are currently burning across 13 American states, and many more are active across Canada.

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