PHILADELPHIA -- As an orange haze of wildfire smoke from Canada smothers parts of the eastern US, officials are warning residents in both countries of unhealthy or hazardous air Wednesday.
More than 55 million people in the eastern US are under air quality alerts due to the smoke. The heaviest smoke is forecast to impact the Northeast through the Mid-Atlantic and down to the Carolinas, and smoke conditions in those regions could last through at least Thursday.
Major metro areas in Pennsylvania, New York, New Jersey and Connecticut now have air quality indexes (AQIs) above 150 - which is considered "unhealthy," according to the government website AirNow.gov.
Philadelphia had an AQI of 205 as of Wednesday morning, which is classified as "very unhealthy."
New York City; Jersey City, New Jersey; and New Haven, Connecticut all had "unhealthy" AQIs ranging from 155 to 171 on Wednesday morning.
And the Canadian capital of Ottawa is getting hit with some of the worst air quality, according to AirNow.gov, a partnership of the US Environmental Protection Agency, the National Oceanic and Atmospheric Administration, the US Centers for Disease Control and Prevention and other agencies.
While New York City, Philadelphia and Washington, DC, are expected to see their air quality improve throughout the day, the air over Boston, Pittsburgh and Raleigh, North Carolina, is expected to get worse Wednesday.
Live updates on the smoke's spread:
FAA lifts ground stop at NYC airport but delays flights due to smoke
The Federal Aviation Administration lifted a ground stop for flights bound for New York's LaGuardia airport due to smoke, but has delayed some flights on the ground.
Flights into Philadelphia are also being impacted because of the wildfire smoke, the FAA says. It reported the average delay is about a half-hour. A similar delay to the one at LaGuardia is in place in Newark.
"The FAA has slowed traffic to and from the New York City area airports due to reduced visibility from wildfire smoke," the FAA told CNN in a statement. "The agency will adjust the volume of traffic to account for the rapidly changing conditions."
As of 2:45 p.m. ET, airlines in the U.S. have canceled 120 flights and delayed another 1,928, according to data from tracking site FlightAware.
The Federal Aviation Administration says the extreme wildfire smoke haze lingering over the Northeast U.S. due to Canadian wildfires could delay flights through Boston, New York, Philadelphia, Baltimore, and Washington, D.C.
'Code red' in Philadelphia
Philadelphia issued a "code red" alert Wednesday, warning certain residents should stay indoors.
The elderly, young children and those who are pregnant or have heart or lung conditions could experience serious health effects from the smoke, said James Garrow, spokesperson for the Philadelphia Department of Public Health.
"For those who are not considered to be in a sensitive group, we are asking those folks to avoid strenuous activities outdoors like jogging or exercising," Garrow told CNN Wednesday.
"We are asking folks to avoid unnecessary time outdoors," he said.
"But if they need to be outdoors, they should be masked and head inside as often as they need."
Garrow said it's not clear how long the code red alert will last, "or if it will change to another level of warning."
The world's most polluted major city
New York City had the worst air pollution of any major city in the world at one point Tuesday night, before dropping to second-worst behind New Delhi, India, according to air quality tracker IQair.
The smoke has also triggered air quality alerts in parts of Massachusetts, New Hampshire, Pennsylvania, Maryland, Virginia and the Carolinas, according to the National Weather Service.
Air quality in the US Northeast has deteriorated this week as more than 150 wildfires rage in Quebec, according to the Canadian Interagency Forest Fire Center.
In Quebec, the entire town of Chibougamau - population 7,000 - is under a mandatory evacuation order as fast-moving wildfires wreak havoc across the region.
"Given the current situation, the mayor of Chibougamau, Manon Cyr, has declared a state of emergency and announced the mandatory evacuation of the entire town, including the resort area," the town announced in a Facebook post Tuesday night.
So far this year, the province has endured more than 400 wildfires, which is twice the average for this time of year.
More than 9 million acres have been charred by wildfires in all of Canada this year - about 15 times the normal burned area for this point in the year.
The alarming air quality prompted New York Mayor Eric Adams to ask residents to limit their outdoor activity and state environmental officials to issue an air quality health advisory for the city through Wednesday.
"Active children, adults, and people with lung diseases such as asthma should reduce prolonged or heavy exertion outdoors," New York City Emergency Management said.
The nation's largest public school district canceled all outdoor activities Wednesday, but will remain open. At least 10 school districts in central New York state canceled outdoor activities and events Tuesday.
Overnight Tuesday into Wednesday, the air quality index for the city topped 200, pushing it into the "very unhealthy" range, according to air quality tracker AirNow. By 7 a.m. Wednesday, New York City's air quality index was just below 180, a designation of "unhealthy."
Human-induced climate change has exacerbated the hot and dry conditions that fuel wildfires.
Scientists recently reported that millions of acres scorched by wildfires in the Western US and Canada - an area roughly the size of South Carolina - could be traced back to carbon pollution from the world's largest fossil fuel and cement companies.
Why wildfire smoke can be hazardous
Wildfire smoke is particularly dangerous because it contains tiny particulate matter, or PM2.5 - the tiniest of pollutants.
When inhaled, it can travel deep into lung tissue and enter the bloodstream. It comes from sources like the combustion of fossil fuels, dust storms and wildfires, and has been linked to several health complications including asthma, heart disease and other respiratory illnesses.
And the impacts could be deadly: In 2016, about 4.2 million premature deaths were associated with fine particulate matter, according to the World Health Organization.
"If you can see or smell smoke, know that you're being exposed," said William Barrett, the national senior director of clean air advocacy with the American Lung Association. "And it's important that you do everything you can to remain indoors during those high, high pollution episodes, and it's really important to keep an eye on your health or any development of symptoms."
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