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Thick haze blanketed the Twin Cities metro area and other parts of Minnesota Saturday as strong winds continued to blow smoke from ­forest fires in Canada hundreds of miles south.

The smoke is from dozens of ­wildfires burning in northern ­Saskatchewan.

The air quality in the greater Twin Cities area was “unhealthy for sensitive groups” Saturday evening, according to the Minnesota Pollution Control Agency (MPCA). It was worse to the northwest, in the Brainerd and Detroit Lakes areas, where there was a red zone labeled “unhealthy” on the MPCA’s ­air-quality map. Duluth, Marshall and Rochester were all in slightly clearer “moderate” zones.

Smoke has been blowing as far south as Tennessee, with a thick haze extending through much of North Dakota, South Dakota, Minnesota, eastern Nebraska, Iowa, Illinois and Missouri.

During the holiday weekend, fireworks also produce air pollutants, including particulate matter, that are linked to short-term or long-term health effects. A recent National Oceanic and Atmospheric Administration study showed a particularly high spike in air pollution after fireworks displays.

The new research shows a spike usually happens on July 4 from 9 to 10 p.m., when nighttime displays take place. Levels drop back down by noon on July 5, according to the research. Average concentrations over the 24-hour period starting at 8 p.m. are 42 percent higher than on the days preceding and following the holiday.

The study monitored air-quality measurement sites on July 4 from 1999 to 2013.

Air pollutants from fireworks can cause symptoms including coughing, wheezing, shortness of breath and asthma attacks, according to the study. Those with heart or lung disease, older adults and children are most vulnerable, and are urged to avoid exertion.

The Environmental Protection Agency recommends people who are sensitive to air pollution limit their exposure by watching fireworks as far away from the source as possible and limiting time outdoors when forest fire haze is present.

Weather forecasters predict the haze will clear up in the next few days.

But pollution or no, Sunday may well be another day where exertion may be inadvisable. Temperatures in the metro area are expected to soar into the upper 80s, and humidity will be high. Showers and thunderstorms are likely Sunday night, with cooler weather returning Monday.

The Associated Press contributed to this report

Karen Zamora • 612-673-4647

Twitter: @KarenAnelZamora