Suburban fire, health and emergency management departments grappled Tuesday with a pervasive pall of smoke that poured over the region from a huge wildfire in northern Minnesota, more than 400 miles away.
Authorities said the smoke is coming from the 60,000-acre Pagami Creek wildfire, sparked Aug. 18 by a lightning strike near Ely, Minn., in the northeastern part of the state.
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The Illinois EPA rated Chicago air as "orange" -- unhealthy for children, elderly and those with respiratory or cardiac conditions -- with a particulate reading of 135 at 5 p.m.
Small particulates like those in smoke can harm a person's health because they can pass into the lungs, according to the U.S. EPA website.
The haze first descended on the Northern suburbs about midmorning and edged into the West and Northwest suburbs by early afternoon, sending firefighters from several departments out in search of fires that didn't exist.
"We've gone out on a couple of calls," said Libertyville Fire Chief Rich Carani. "We'd get out there and realize (the smoke) was everywhere."
"It was pretty pervasive," Antioch Fire Chief John Nixon added. "A lot of people were describing it as burning plastic or electrical -- it's a pungent smell."
Experts said smoke from the fire has been caught in the jet stream and pushed across Wisconsin, into the Chicago region and on to Michigan. Northerly winds behind a cold front combined with sinking air and brought the smoke this far.
The problems were expected to continue overnight, said Samuel Shea, a meteorologist at the National Weather Service. More westerly winds in advance of another cold front early Wednesday morning should bring relief, the weather service said.
"Smoke will likely continue to spread to the southeast, across much of northeast Illinois and northwest Indiana through this evening. Expect hazy skies and a distinct burning odor," the service said on its website, crh.noaa.gov/lot/.
A report on the fire is on the weather service's site.
The fire started Aug. 18 in the Boundary Waters Canoe Area Wilderness on the Minnesota/Canadian border, but it first began spreading quickly this week in windy, dry conditions. The fire raced 16 miles east in a single day from Monday to Tuesday.
"Nobody would have guessed it would be doubling and quadrupling in size," said Jean Bergerson, a spokeswoman for the Minnesota Interagency Fire Center.
No structures have burned and no one has been hurt, Bergerson said. But 25 mph winds forecast for Tuesday and Wednesday were likely to spread the fire, dubbed the Pagami Creek Fire for its point of origin. She predicted it would be days or weeks before the fire was under control.
About 120 campers were evacuated from the fire zone earlier this week, as were people in 36 homes on the eastern edge of the fire.
The residents of Isabella, a small town of about 200, were told to be ready to leave on short notice, she said.
Parts of the boundary waters area remained open to campers and canoers.
About 200 firefighters were assigned to the fire on Tuesday and more were pouring into the area. Bergerson said the first of a group of about 50 elite firefighters were coming in from the Rocky Mountains and would probably take over on Thursday.
Gov. Mark Dayton announced Tuesday he was sending in four Minnesota National Guard helicopters equipped with huge buckets for water drops to assist the firefighters.
In the Chicago suburbs, the Lake and McHenry county emergency management agencies said they received reports of residents having difficulty breathing and reporting irritated eyes and headaches from the smoke. The Kane County Emergency Management Center issued a weather alert.
Along with state agencies, the county emergency agencies recommend that children, elderly residents and those with respiratory or cardiac problems stay indoors with air conditioning on and avoid exertion while air quality remains poor. Anyone with pre-existing health conditions should be watched carefully, according to a statement from the Illinois Department of Public Health.
Cooper Middle School in Buffalo Grove canceled after-school activities because of the air quality, according to the schools' websites.
Several municipalities sent out news releases or notices to residents explaining the situation, including Cary, Crystal Lake, Elgin, Geneva, Hanover Park, Naperville and Wheeling.
• Daily Herald news services contributed to this report.