CHICAGO — Air quality in Chicago plummeted this week to some of the worst levels in the world, with officials reporting “very unhealthy” conditions due to smoke from Canadian wildfires blanketing the region.

As of July 31, air quality index (AQI) readings across the city ranged from 160 to 172, driven primarily by fine particulate matter (PM2.5). These levels far exceed safety thresholds and have triggered Red Air Pollution Action Day alerts from the Illinois Environmental Protection Agency. The thick haze and poor visibility are expected to continue into early August.

The primary cause of the poor air quality is smoke drifting south from large-scale wildfires currently burning in Canada’s Manitoba and Saskatchewan provinces. Weather patterns, particularly a high-pressure system sitting to the north of Illinois, have stalled atmospheric movement, trapping smoke over the region. In addition, temperature inversions have prevented the smoke from dispersing, causing it to linger at ground level where it poses the most harm to residents.

Chicago’s already elevated pollution levels — from dense road traffic, rail and air transport, and industrial activity — have intensified the effects of the smoke. Combined with the stagnant weather conditions, this has created a perfect storm for poor air quality.

Residents across the city have been advised to remain indoors, limit outdoor activity, and use high-efficiency air purifiers. PM2.5 levels reached nearly 70 micrograms per cubic meter, more than 13 times the World Health Organization’s recommended limit.

While weather models suggest conditions may begin to improve in the coming days, officials warn that the region may continue to see unhealthy air if Canadian wildfire activity persists or intensifies.

For now, Chicagoans are urged to take precautions, particularly children, seniors, and those with respiratory conditions. The city’s air remains under close watch as public health agencies monitor developments.