New York City had the worst air quality in the world on Wednesday afternoon as smoke from Canadian wildfires drifted into the area, according to IQAir, a Swiss air monitoring company.
The authorities urged people to wear masks and all outdoor activities for schoolchildren were banned as the sky turned a hazy orange colour.
Philadelphia has become the new epicentre for the smog from Canadian wildfires after the air quality was deemed “hazardous”.
Here is all you need to know about the ongoing wildfire smoke engulfing US cities.
Why is the sky orange in the US?
Wildfires across Canada have prompted the evacuation of more than 20,000 from their homes.
Around 11,400 of those are from remote areas in northern Quebec, while another 4,000 were told evacuation could be imminent.
Indigenous communities have been disproportionately affected, with Oujé-Bougoumou, a Cree community situated around 750km north of Montreal, told to evacuate on Tuesday night.
Millions of people in the US have been under air quality alerts as smoke from the Canadian wildfires has drifted across the border.
The smoke has been pushed south and then east by a storm system off the Novia Scotia coast.
It is forecast to continue travelling south down the US, reaching as far as South Carolina.
Which US cities have been affected?
Philadelphia has become the new epicentre of the toxic smog after New York City took the brunt of it earlier in the week.
In New York, people were urged to wear masks and many outdoor activities were halted, including the regular baseball game at Yankee Stadium between the Yankees and White Sox.
An air quality index recorded 431 out of 500 in Philadelphia last night, with the smog reaching “hazardous” levels, according to Air Now.
The index is a measure of five common pollutants, with a rating of over 150 considered “unhealthy”.
Philadelphia Public Health announced they had gone to “code red” due to air pollution and Air Now urged residents to stay indoors and refrain from unnecessary activity.
People have been urged to wear high-quality face masks outside, refrain from strenuous activities and keep air circulating in their homes using fans and air conditioning units.
A baseball game between the Philadelphia Phillies and the Detroit Tigers was cancelled.
The air quality in Washington DC has also reached code red, meaning it is unhealthy for the general population to be outside.
Air quality alerts have also been introduced in Massachusetts, New Hampshire, New York, Maryland, Illinois, Virginia and the Carolinas, according to the National Weather Service.
What action has been taken?
On Wednesday night, President Joe Biden made orders to deploy “all available federal firefighting assets” to help fight the wildfires.
Smoke has been filtering from Canada into the US since last month, but the problem intensified as a series of fires in Quebec have become out of control.
The White House said the US President made the orders after speaking with Canadian Prime Minister, Justin Trudeau.