Smoke from raging wildfires in Canada triggered poor air quality alerts in several cities across the upper Midwest on Tuesday, with Chicago, Minneapolis and Detroit recording some of the worst air pollution levels of any major city in the world.
Why it matters: Smoke from unprecedented Canadian wildfires, which have been exacerbated by human-caused climate change and global warming, has repeatedly choked North American cities this summer, and additional rounds of smoke may follow.
- Canada is experiencing its worst wildfire season on record, driven by extreme heat events and exacerbating drought conditions, according to data from the Canadian Interagency Forest Fire Center.
- Winds also carried the smoke across the Atlantic Ocean, shrouding the sun in parts of Portugal and Spain on Tuesday.
Threat level: Inhaling wildfire smoke when its present in high concentrations at ground level can cause serious health complications and is especially dangerous for elderly populations and people with heart ailments or asthma.
- An air quality action day was declared for all of northeast Illinois and northwest Indiana for Tuesday and Wednesday, meaning fine particulate matter and other pollutants could build to unhealthy levels in the outdoor air.
- Air quality alerts across the Upper Midwest are expected to remain in effect until Thursday, according to the National Weather Service.
By the numbers: Chicago had the world's worst air quality for major cities around the world on Tuesday afternoon with a 198 — or a code red — on the Air Quality Index (AQI), which is considered dangerous for sensitive groups, according to Swiss air technology company IQAir.
- Minneapolis and Detroit followed.
- Grand Rapids, Michigan, which isn't included in IQAir's ranking system, had an AQI of 251, or a code purple, which is "very unhealthy" for all groups of people, according to AirNow.
- Milwaukee, Wisconsin, also recorded a code purple with an AQI of 237.
Zoom in: The smoke caused a thick haze in downtown Chicago, reducing visibility at Chicago-O'Hare International Airport to 1.25 miles.
- People in Milwaukee also saw a strong smog that reduced visibility to around 1.75 miles.
- A thinner haze and the smell of smoke also blanketed Indianapolis.
The big picture: Nearly 500 wildfires were burning across Canada on Monday, including 258 out of control fires.
- To date, 2,957 fires in Canada have burnt 19.3 million acres (7.8 million hectares), which is an area equivalent to all of Michigan's forest land.
Go deeper: Heat wave affects 45 million people from Southwest to Miss. Valley
