Smoky conditions persist across much of the US

At least 10 states from the Midwest to the Northeast will experience smoky conditions again on Friday caused by raging wildfires across Canada, capping a week in which millions of people struggled with poor air quality.

Smoke that has obscured skylines and made it hard for some to breathe was expected to linger into the July 4 long weekend, according to the National Weather Service. However, air quality was expected to slowly improve as thunderstorms help spread the smoke.

A health advisory for air quality was in effect for the entire state of New York on Friday.

As of 7 a.m. Eastern Time, New York City had an Air Quality Index of 156, making it unhealthy. A reading of 301 or higher is considered dangerous. Similar air quality levels were reported Friday morning in Cleveland, Detroit, Milwaukee and Washington, DC

Some of the worst air quality in the country on Friday was in Pennsylvania, where Pittsburgh’s AQI was 191, according to AirNow.gov. A code red advice was applies to the entire statemeaning vulnerable residents were urged to stay indoors.

For much of the week, the Great Lakes region, parts of the Midwest and the Northeast were choked with smoke, forcing residents to stay indoors to avoid unhealthy air. Those forced to leave the house for work, errands or other activities disguised themselves to stay safe.

They were there on Friday morning nearly 500 wildfires across Canada, nearly half of which are out of control, according to the Canadian Interagency Forest Fire Center. Canada’s wildfire season started several weeks earlier this year, meaning the fires could affect air quality in North America for weeks.