Welcome to this insightful piece on the impacts of hazardous wildfire smoke, particularly as it has affected the Great Lakes region and reached the East Coast. The latest post by Jeff Masters highlights the repercussions of this event, detailing not only the environmental crisis but also its staggering health implications. Though the most intense pollution may have subsided, the dangers are far from over.
As climate change leads to more frequent and severe wildfires, planning for bad air quality has become essential. Jeff Masters elaborates on the risks associated with wildfire smoke and its deep ties to global warming. For those exposed to high levels of PM2.5 pollution, investing in a good air filter can significantly improve air quality. However, during periods of hazardous air, a respirator is advisable. Here’s one model I personally recommend:
This respirator may fit snugly but provides more comfort for sleeping than an N-95 mask. I often switch to this style when flying because it allows for easier breathing. On long-haul flights, I’ve noticed that I tend to inhale harder when trying to sleep, likely compensating for lower oxygen levels.
By Jeff Masters, a former hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. He co-founded Weather Underground in 1995 and served as its chief meteorologist and board member until its sale in 2012. Originally published at Yale Climate Connections.
Wildfires in northern Minnesota and Ontario have led to thick smoke blanketing vast areas of North America, impacting tens of millions with unhealthy pollution levels.
This incident has resulted in record-setting poor air quality across the Great Lakes, Mid-Atlantic, and Northeast of the United States. This hazardous air, primarily due to PM2.5 particles—tiny pollutants less than 2.5 microns in diameter—has consistently remained within the “Hazardous” range across five states since Wednesday morning.
Yesterday, Duluth, Minnesota, which has previously touted itself as a climate haven, registered the highest air quality index (AQI) in the nation. The city recorded an astonishing 934 AQI for PM2.5, more than three times above the “Hazardous” threshold and topping its previous record of 159 set on July 20, 2021. The EPA has been tracking this data since 1999.
Record Poor Air Quality
Duluth: 934 AQI for PM2.5 (Old record: 159, July 20, 2021)
Chicago: 511 (Old record: 246, June 28, 2023)
Detroit: 490 (Old record: 226, June 28, 2023)
Cleveland: 297 (Old record: 285, June 28, 2023)
Milwaukee: 414 (Old record: 270, June 27, 2023)
Flint: 343 (Old record: 178, June 27, 2023)
These photos of FNs community members fleeing their homes by boat are genuinely apocalyptic
(Photo via Wayne Wastaken of Collins, Ontario, who says his “hometown is gone”)
www.facebook.com/share/r/1ArN…
— Luke LeBrun (@lukelebrun.ca) July 15, 2026 at 10:18 PM
Due to the unprecedented number of individuals affected, coupled with an ongoing heatwave, this widespread pollution episode will likely lead to hundreds, if not thousands, of premature fatalities. A previous study linked a similar smoke event in 2023 to approximately 33,000 premature deaths in the United States, 8,300 in Canada, and 23,000 in Europe. The EPA defines a premature air pollution death as one occurring an average of 14 years earlier than it would have otherwise.
The AQI in Toronto this morning is 170-180, solidly in the Red “Unhealthy” range.
— Dr. Jeff Masters (@drjeffmasters.bsky.social) July 15, 2026 at 9:42 PM
Woah. It’s raining ashes due to wildfire smoke in the Upper Peninsula of Michigan.
Source: www.threads.com/@michiganuns…
— Dr. Lucky Tran (@luckytran.com) July 16, 2026 at 10:54 PM
The Connection Between Climate Change and Wildfires
As temperatures rise, the risk of wildfires increases because warmer air holds more moisture, leading to dehydration in plants and creating conditions ripe for intense fires that produce substantial smoke. The recent wildfires were fueled by extreme heat conditions made up to five times more likely by climate change (Fig. 1). Climate Central notes that the heat fueling these fires would have been “highly unlikely” in a world devoid of climate change.
3/ When wildfire smoke occurs during heatwaves in areas where a portion of the population doesn’t have access to air conditioning, people face the dilemma of opening their windows to avoid heatstroke, but searing their lungs with smoke. Smoke + heat can become even deadlier than either alone.
— Jonathan Vigh (@skywatcher77.bsky.social) July 15, 2026 at 7:40 AM
2/ Known as the “silent killer”, long-term exposure to wildfire smoke is estimated to kill ~24,000 people per year in the U.S. There is no safe level of wildfire smoke exposure, with mortality effects estimated to occur up to 3 years after exposure.
www.science.org/doi/10.1126/…
— Jonathan Vigh (@skywatcher77.bsky.social) July 15, 2026 at 7:40 AM
Five States Recorded “Hazardous” Air Quality on Thursday
On Thursday, July 16, parts of Ontario and five U.S. states—Minnesota, Wisconsin, Michigan, Illinois, and Ohio—registered 24-hour PM2.5 AQI levels within the “Hazardous” (brown) range. According to the U.S. Environmental Protection Agency, this situation warrants emergency health warnings, affecting the entire population. Additionally, “Very Unhealthy” air was documented in New York, Pennsylvania, and Indiana, where health alerts require vigilance from everyone—not just those with pre-existing vulnerabilities.
Ryan Stauffer, an air pollution scientist, indicated that this current air pollution event surpasses the extremity of the 2023 wildfire smoke incident in this region. During that earlier event, only about three EPA monitors in Pennsylvania reported a 24-hour AQI in the hazardous range. However, on the recent Thursday, as many as 50 EPA monitors recorded similarly hazardous levels (Fig. 2), with an additional nine in Ontario. Notably, Detroit was ranked as the most polluted major city globally for most of Thursday, with Chicago overtaking it later that night. By Friday morning, the top five most polluted cities worldwide were all located in North America: Detroit, Chicago, Washington D.C., Toronto, and New York City.
Hourly readings exceeded 1,000 AQI in Minnesota, Wisconsin, and Michigan. The “Hazardous” threshold begins at an AQI of 300, meaning these numbers were more than three times above that level. The most extreme reading, an astonishing AQI of 3,567, occurred in northern Minnesota downwind of Boundary Waters park, where fires were rapidly spreading.
At 4:50 pm Wednesday, July 15, Sea Gull Lake, MN, hit an AQI of 3567. Anything over 300 is Hazardous, so this was over 11x higher than the Hazardous threshold. This is a location downwind of the out-of-control fires in Boundary Waters Park.
— Dr. Jeff Masters (@drjeffmasters.bsky.social) July 17, 2026 at 12:31 AM
How the Situation Evolved: Record Heat and a Robust High-Pressure System
The outbreak of wildfires commenced on Monday, where an unprecedented upper-level ridge of high pressure experienced in the north-central U.S. raised temperatures, exacerbating pre-existing moderate to severe drought conditions. Thunder Bay, Ontario, recorded a sweltering 39.5 degrees Celsius (103.1°F), shattering its previous heat record. The region was further challenged by winds that exacerbated the spreading of multiple wildfires, igniting dry vegetation, including dead trees from a past spruce budworm infestation and a major derecho event.
As a result, extreme fire conditions emerged, characterized by rapid fire spread and pyrocumulus clouds—enormous thunderstorm-like formations triggered by the intense heat of the fires. Tomer Burg has provided an insightful discussion on the meteorology leading to this wildfire event in an excellent thread:
Parts of the Northeast US have been under a thick plume of smoke today overspreading the region from fires across south-central Canada – the worst smoke plume to affect the region since the infamous 2023 NYC smoke plume.
Thread for the meteorology associated with this:
— Tomer Burg (@burgwx.bsky.social) July 16, 2026 at 4:10 AM
The Current Landscape: Over 20 Large Fires Uncontrolled
As of Friday, there were 193 active fires covering an area of 1.7 million acres (673,000 ha) in Ontario, with most deemed “out of control” according to the Canadian Interagency Forest Fire Centre. Out of the 22 larger fires nearing the U.S. border, 18 were receiving full firefighting efforts, and four remained unaddressed. In northern Minnesota, the National Interagency Fire Center reported six large fires, all at 0% containment, spanning 60,000 acres.
The Outlook: A Promising Change for the Worst-Hit States
Thunderstorms passed through the Minnesota/Ontario fire region on Friday morning, bringing up to two inches of rain, aiding firefighting efforts. However, the fire danger index in Ontario remains high to very high, and these storms may have ignited new fires.
The cold front accompanying the storm is expected to help clear much of the smoke from Chicago and Wisconsin by Friday afternoon and Michigan by early Saturday morning. However, more smoke is anticipated for Michigan and Wisconsin Saturday night into Sunday, leading to additional “Hazardous” AQI conditions. Another wave of smoke is predicted to move deep into central U.S. states on Wednesday, possibly reaching Arkansas and Missouri.
Many of the significant smoke-producing fires in Minnesota and Ontario are expected to persist for a considerable duration, with some continuing until snowfall in October. The long-range fire assessment (Fig. 3) suggests above-normal fire risks across extensive forested regions in northern Canada and the western U.S. this summer. July and August usually mark the peak of the fire season, extending into mid-September. Additionally, a potent North American Monsoon is currently delivering heavy rain to parts of the southwestern U.S., which may lower overall fire risks in that area by August.
Recently, numerous lightning-induced fires erupted in the Pacific Northwest. With hot, gusty conditions expected next week, these fires may escalate and produce significant smoke.
A major new wildfire outbreak is now underway across the interior Pacific Northwest, with dozens (or more) new wildfires already popping up in eastern Oregon & Washington following tens of thousands of lightning strikes in a region experiencing moderate to extreme drought. #ORwx #WAwx
— Daniel Swain (@weatherwest.bsky.social) July 17, 2026 at 7:04 AM
Many new wildfire starts are being reported, particularly in the Cascades and Blue Mountains of Oregon, following a dry thunderstorm outbreak yesterday and overnight.
#ORfire #ORwx #WAfire #WAwx
— Mark Ingalls (@ingalls.mstdn.ca.ap.brid.gy) July 16, 2026 at 10:13 PM
Future Projections: Climate Change to Intensify Wildfire Risks
The number of individuals in the U.S. who experience at least one day of smoke-related fine particle pollution at levels three times above the EPA standard has surged 27-fold over the past decade. As climate change continues to assert its effects, we can expect wildfire smoke challenges in North America to worsen significantly.
A recent study published in Nature Ecology & Evolution concluded that the frequency and severity of extreme wildfires have doubled globally over the last 21 years due to climate change. With rising temperatures come periods of hotter, drier weather, creating ideal conditions for wildfires to ignite.
For those seeking to learn more, here are additional resources on climate change and wildfires:
Fantastic post on why wildfires in Canada’s forests are much different than in the western U.S. “Canada’s area burned has surged, and it has surged in step with warming: hot, dry fire seasons burn far more forest, with area burned rising roughly 80% for each 1°C increase in temperature.”
— Dr. Jeff Masters (@drjeffmasters.bsky.social) July 17, 2026 at 11:46 PM
