31-07-2025
Air quality alerts issued across Illinois. But how safe are you inside your home?
Air quality alerts issued Thursday in Illinois because of Canadian wildfire smoke marked the latest bout in an increasingly common summer occurrence. The alert covers 34 Illinois counties designated as having unhealthy air for all residents.
Although it is recommended to hunker inside during these stretches, experts say indoor air quality can often be just as bad, if not worse, than outdoor air quality.
'When they're in the home, their windows are closed, the doors are shut and locked, and they think, 'this is my indoor air, and it's totally different than what's in the outdoor air,'' said Ian Cull, founder and chief science officer of Indoor Science, an indoor air quality consulting and training company headquartered in Aurora. 'But homes and all buildings are leakier than what people imagine.'
There were two multi-day periods of bad air quality in the Midwest earlier this summer — both due to smoke from Canadian wildfires. In June, Chicago saw three days of some of the worst air quality in the world, and in mid-July, air quality was bad enough for the Illinois Environmental Protection Agency to declare an 'Air Quality Action Day' – when air quality is at least unhealthy for sensitive groups for two or more consecutive days. Thursday afternoon, Chicago's air was ranked worst in the world, according to Swiss air quality technology company IQAir.
But staying indoors with air conditioning doesn't offer complete protection — nor does it necessarily mean that your indoor air quality was good to begin with.
'Wildfire smoke contains particles that are so small they can get through ventilation system filters and AC units,' said Susan Buchanan, clinical associate professor of environmental and occupational health sciences at University of Illinois at Chicago.
Fine particulate matter is defined as particulate matter measuring 2.5 micrometers or smaller. For comparison, the width of a human hair is about 80 micrometers. These particulates are the biggest and most dangerous pollutant in wildfire smoke.
In the short term, fine particulate matter causes irritation of the eyes and respiratory system, with symptoms mimicking allergies or the common cold. Long-term exposure to wildfire smoke is still being studied, but exposure to other fine particulate matter causes a wide variety of health effects, including decreased lung function and heart issues or heart attacks.
But even when outdoor air is considered healthy, indoor air quality can often be much worse than what's outside. That's because indoor products like cleaning supplies, candles, and even spray deodorant can significantly worsen indoor air quality, according to a series of studies released by Purdue University in February. Cooking fumes, dust, smoking indoors, and pet dander also bring down air quality.
In addition, most homes are underventilated, or they rely on air conditioning systems that recirculate the dirty indoor air. That's why even when a home air purification system is in place, Cull said it's generally a good idea to open doors and windows every day or so to bring in fresh air.
'The whole benefit of ventilation is to flush out some of the contaminants that we've created,' Cull said. 'But then the tables are turned when outdoor air quality is bad. Then, indoor air, despite its chemicals from cleaners and personal care products, ends up being better than the outdoor air.'
Air quality is measured on a scale of 0 to 500 by the U.S. Environmental Protection Agency, with 0 being good and anything above 300 being hazardous. The value is calculated from tracking five factors: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. When air quality is above 100, sensitive groups are advised to limit outdoor time, and above 150, like it is Thursday, air quality is unhealthy for everyone.
According to experts, climate change is increasing the intensity, frequency and reach of the Canadian wildfires.
Buchanan recommended that people check the Air Quality Index online every day.
'People with respiratory conditions like asthma, pregnant people, and the elderly should stay indoors in AC,' she said.
To keep indoor air as clean and fresh as possible, the Illinois Department of Public Health recommends that people minimize the amount of indoor-air pollutants they use. Chemical cleaning should wait until the air quality improves, and fuel-burning stoves should not be used.
When these recommendations can't be followed, especially when outdoor air quality is bad for an extended period of time. Cull and Buchanan said a standalone air purifier is the best ally.
Cull said that air purifiers with HEPA filters are the best for improving air quality. HEPA, which stands for high efficiency particulate air, is the highest standard of air filter, with the ability to remove at least 99.97% of the most common microscopic pollutants and particulate matter from the air. This includes pet dander, dust, pollen, mold, and even bacteria.
Cull also warned that some air filters are known to produce ozone as a byproduct when they remove particulates from the air. This is most commonly seen in air purifiers with ionizers or UV light components.
Dr. Momen Wahidi, an interventional pulmonologist and medical director of Northwestern Medicine's Canning Thoracic Institute, says that hospitalizations only went up a little bit during the last two air quality alerts in Chicago this year — but that doesn't mean that this is not an issue.
'I know I've dealt with this about a month or two ago, again from the wildfire,' he said. 'We're probably going to see this issue popping up more often.'
