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New York City 's Statue of Liberty sits behind a cloud of haze from the western wildfires. Photo: Spencer Platt/Getty Images

Smoke from the wildfires engulfing the U.S. West and Canada and carrying harmful air pollution has triggered air quality alerts in the Upper Midwest and East Coast cities including New York, Philadelphia and Washington, D.C., on Wednesday, according to the National Weather Service.

Driving the news: The coast to coast smoke, which is clearly visible from space, is due to the nearly 300 wildfires burning in British Columbia and the more than 80 large blazes in the U.S.

  • The towering pyrocumulus clouds coming off these fires is lofting smoke all the way into the stratosphere, and the jet stream is carrying the smoke eastward across the country.

Our thought bubble: Due to the presence of small particulate matter, wildfire smoke can be hazardous to human health, even many, many miles downwind. The fires are also a source of carbon dioxide emissions, thereby acting to worsen global warming.

By the numbers: Smoke from the fires blanketed New York City sending its air quality index to an 170 before dropping to a still-unhealthy 158 on Tuesday — second only to the AQI of 174 in Krasnoyarks, Russia.

  • Boston, Massachusetts, and Hartford, Connecticut, also recorded unhealthy AQI readings that were higher than 150 on Tuesday.

Context: The wildfires, many of which started when a severe heat wave erupted in June, have been linked by scientists to human-caused climate change.

In photos:
A haze over the Manhattan skyline on July 20. Photo: Spencer Platt/Getty Images
Sunlight interacting with wildfire smoke, causing the sun to appear with a reddish-orange tint in New York City on July 20. Photo: Lokman Vural Elibol/Anadolu Agency via Getty Images
The Statue of Liberty barely visible in the distance in New York City on July 20. Photo: Spencer Platt/Getty Images

Editor's note: This story has been updated throughout.

Go deeper

Updated Aug 3, 2021 - Sports

In photos: Tokyo Olympics day 11 highlights

Jrue Holiday, #12 of Team USA, drives to the basket against Spain during their men's basketball quarterfinal on day 11 of the Olympic Games at Saitama Super Arena on Aug. 3 in Saitama, Japan. Holiday scored 12 points for the U.S. during the game. Photo: Charlie Neibergall - Pool/Getty Images

Day 11 of the Tokyo Olympic Games saw Norway's Karsten Warholm smash the world record in the 400-meter hurdles — and so did the second-placed American Rai Benjamin on Tuesday.

Of note: In men's basketball, Team USA overcame a tough challenge from Spain to win 95-81 and advance to the semifinals — with Kevin Durant scoring 29 points for the Americans.

12 hours ago - Sports

In photos: Tokyo Olympics day 12 highlights

Team USAs Sydney McLaughlin in front of the timer after winning the 400m hurdles in record time at the Tokyo Olympics. Photo: Wally Skalij /Los Angeles Times via Getty Images

Day 12 of the Tokyo Olympic Games saw American Sydney McLaughlin break her own world record to win gold in the women's 400-meter hurdles final on Wednesday.

Of note: Japan won a third Olympic skateboarding gold, as two teenagers and a 12-year-old swept the podium for the inaugural women's park skateboarding event.

Manhattan, Westchester prosecutors request evidence from Cuomo investigation

Gov. Cuomo during a press conference in New York City on Aug. 2. Photo: Lev Radin/Pacific Press/LightRocket via Getty Images

The district attorneys for Manhattan and Westchester County on Wednesday requested evidence related to New York Attorney General Letitia James' investigation into sexual harassment allegations against Gov. Andrew Cuomo (D), according to a letter obtained by NBC News.

Why it matters: The district attorneys are investigating if alleged conduct highlighted in an independent report published by James' office that occurred in their jurisdictions was criminal in nature.