CHICAGO (WLS) -- An air quality alert was issued for the greater Chicago area on Tuesday.

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The alert was issued by the EPA at about 11:56 a.m. It will be in effect until midnight.

Lake, Porter, Newton and Jasper counties in Indiana are also under alert all day Tuesday.

The Chicago area has been under air quality alerts for most of last week, due to smoke from Canadian wildfires.

At one point last week, Chicago had the worst air quality in the world.

At least 738 wildfires are currently burning in Canada, with at least 201 out of control, according to the Canadian Interagency Forest Fire Centre.

Medical experts said the unhealthy air conditions are of most concern for active children and adults who have a respiratory condition.

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