Nearly a third of Americans were experiencing poor air quality on Thursday as smoke from Canadian wildfires filled the skies over the Midwest and East, causing unhealthy and, in some spots, dangerous conditions.
Air-quality alerts were in effect until midnight for an area of the US that extends from Wisconsin and northern Illinois into Michigan, New York and the East Coast, the National Weather Service said.
More than 100 million Americans were urged to limit prolonged outdoor activity and, if needed, wear a mask if they suffer from pulmonary or respiratory diseases.
Children and the elderly were also advised to minimise or avoid strenuous activity.
People living in major US cities such as New York, Chicago and Philadelphia may see murky skies and smell burning wood throughout the day.
“Take precautions on Thursday. If you have health conditions, including respiratory conditions such as asthma, reduce your time outdoors,” New York City Mayor Eric Adams said on Twitter.
On Thursday morning, a dull sky hung over Chicago for the third day in a row.
Air quality was "unhealthy” in the third-largest city in the US, which had the poorest air of any major city on the planet, according to IQAir.com, which tracks pollution.
“The air quality in Chicago has been dreadful, giving me brutal migraines. Feeling better today with my trusty air purifier on full blast. Taking a chill day,” said a Twitter user named Skaar.
The air-quality alerts were caused by drifting smoke from wildfires burning in Canada, which is struggling with its worst start to the fire season.
An area of 8 million hectares, bigger than West Virginia, has already burnt. On Wednesday, there were 477 active blazes, about half which were considered out of control, from the Pacific to the Atlantic coasts.
While poor air quality was the concern in the Midwest and East, the US South was again dealing with a heatwave that threatened to persist throughout the day on Thursday and into the long Fourth of July holiday weekend.
The heat index – which measures how hot it feels due to the combination of humidity and temperature – was expected to climb to 38°C and in some spots as high as 46°C.
The weather service urged people to seek air-conditioned spaces and drink plenty of water.
