(NEXSTAR) – Residents in more than a dozen states are currently blanketed in hazy skies and poor air quality as smoke from Canadian wildfires moves through the Midwest and Northeast. For many, the worsening air is expected to stick around for at least another day.

As of Wednesday afternoon, five U.S. cities – Chicago, Detroit, Minneapolis, and Washington, D.C. – rank among the 10 metropolitan areas with the worst air quality in the world, according to IQ Air. Toronto, Canada, had the worst air quality at 186 AQI (air quality index).

Areas in the U.S. are worse though. Decatur, Illinois, 40 miles east of Springfield, had the worst air quality in the country – 282 AQI – as of 4 p.m. ET, according to the Environmental Protection Agency’s AirNow. Cities from Illinois, Ohio, Michigan, and Wisconsin also had AQIs over 220.

Many of the Midwestern cities that have had high AQIs for much of the week are expected to see relief moving into the weekend, but for those in the East and New England, air quality is forecasted to get worse.

The National Weather Service has issued air quality warnings in 15 states as of Wednesday afternoon. In most cases, entire states are under an alert.

Residents in these states remain under air quality alerts through Thursday:

• Delaware
• Illinois
• Indiana
• Iowa
• Kentucky
• Maryland
• Michigan
• Minnesota
• New York
• North Carolina
• Ohio
• Pennsylvania
• Rhode Island
• Tennessee
• Virginia
• Washington, D.C.
• Wisconsin

For those in the Midwest, these alerts are largely in effect through midnight Wednesday night or noon Thursday. For states to the east, like New York, alerts remain in effect through Thursday.

AirNow forecasts that even in states where alerts are set to lift before the end of the day Thursday, air quality will not be entirely back to normal. Minnesota and Wisconsin, for example, are still expected to have moderate air quality, while the air quality in Illinois, Michigan, and Indiana will likely still be unhealthy for sensitive groups.

Rain and storms expected to impact much of the Midwest into Thursday could help clear up the air there, Nexstar’s WGN reports.

The smoke is all coming from Canada, where 490 fires are burning, with 255 of them considered to be out of control. The Canadian Interagency Forest Fire Centre reported Monday that 29,393 square miles of land, including forests, has burned across Canada since Jan. 1. That exceeds the previous record set in 1989 of 29,187 square miles, according to the National Forestry Database.

“As long as the fires are burning and the smoke is in the atmosphere it is going to be a concern not just for Canadians but Americans as well,” Environment and Climate Change Canada meteorologist Steven Flisfeder said.

While it isn’t uncommon for the U.S. to be impacted by Canadian wildfire smoke, the fires aren’t often burning as close to us as they are, WSYR’s Dave Longley tells Nexstar.

“You have to remember that many of these fires in Canada are very remote, basically in the middle of nowhere,” Longley, who has over 30 years of experience in meteorology, explains. “If there is no danger to population centers or infrastructure, they will be left alone to burn.”

The small particles in wildfire smoke can irritate the eyes, nose and throat, and can affect the heart and lungs, making it harder to breathe. Health officials say it’s important to limit outdoor activities to avoid breathing in the particles.

The Associated Press contributed to this report.