NEW YORK (Reuters)

The mass of smoky air that choked New York, Washington and other US cities earlier this week moderated on Friday as it drifted as far south as the Florida Panhandle, and conditions improved to “moderate” along most of the Eastern Seabord.

The US National Weather Service said air quality had improved in areas along the East Coast, but hazy skies and degraded air quality persisted in pockets of the mid-Atlantic, the Ohio Valley and Eastern Great Lakes region.

The haze, emanating from some 400 wildfires burning in Canada—many of them in Quebec province north of New England—was still severe enough on Friday for the weather service to issue air quality alerts for pockets of the Carolinas and elsewhere in the Southeast, as well as in some parts of Texas and Oklahoma.

“That’s due to a combination of both the particle pollution that’s related to the smoke, but also increased ozone levels for those more urban areas,” weather service meteorologist Zack Taylor said.

Further north, air quality alerts remained in effect, including some “Code Orange” designations in Baltimore and Washington, where a day earlier the smoke was thick enough to obscure the top of the 169-metre tall Washington Monument.

The weather service issues “Code Orange” alerts when air quality has degraded to a point where it could affect the health of vulnerable people, such as children and the elderly.

Washington Mayor Muriel Bowser said the quality of the air in the nation’s capital should show further improvement by Saturday.

“We urge residents and visitors to follow precautions related to the ‘Code Orange’ air quality alert,” she wrote in a tweet.

The weather service said there was a chance of showers and thunderstorms in parts of the mid-Atlantic and Northeast.

“That’ll help bring more clouds, and more precipitation will help clean the air a little bit,” Taylor said.

Remote learning returns for a day

Even as conditions cleared in New York and Philadelphia, school districts there reverted to remote learning for all students on Friday. Air quality in Philadelphia was “unhealthy” for sensitive groups in the morning, according to IQAir, a Swiss technology company that measures levels of ozone and fire-generated particulate matter in the air.

Health officials continue to advise millions of Americans to stay indoors if possible to avoid respiratory issues and other health problems that high levels of fine particulates could trigger.

After registering the worst Air Quality Index reading for major global cities for much of the week, New York’s AQI on Friday morning was “moderate” at 74, according to IQAir, pushing it out of the top 25.

Cities and towns in Delaware, Kentucky, Maryland and Virginia experienced the worst air quality in the US, with their AQI readings exceeding 150, considered “unhealthy.”

Canada is experiencing the worst start to the wildfire season on record. More than 2,300 fires this year have charred some 4.3 million hectares (10.6 million acres), according to the Canadian Interagency Forest Fire Centre. Thousands of Canadians have been forced from their homes.

Hundreds of wildfires were still burning in Quebec, while fires spread in British Columbia in the west. Wildfires are common in Canada, but it is unusual for simultaneous outbreaks in the east and west.

Nearly a third of the fires burning across Canada are in Quebec, more than any other province, but provincial premier François Legault said on Thursday the situation there was stabilising.

The United States has dispatched more than 600 firefighters to Canada to help its northern neighbour battle the blazes. President Joe Biden, who has called the wildfires another reminder of the dangers of climate change, said US officials were monitoring air quality and aviation delays.