Canadian wildfire smoke pushed three U.S. cities atop a global air-quality ranking. Here’s how they compare.
Three U.S. cities rose to the top of a global ranking for worst air quality on Friday amid widespread smoke from Canadian wildfires across the Midwest and Northeast.
Detroit recorded a "very unhealthy" U.S. Air Quality Index reading of 240 between 1 and 2 p.m. ET, placing it first among the major cities tracked by Swiss air-quality company IQAir. Chicago followed with an “unhealthy” reading of 199, followed by Washington, D.C. , at 172. New York City placed eighth at 131.
The three worst cities outside the U.S. were Kinshasa, in the Democratic Republic of the Congo, at 186, Delhi, India , at 163, and Jakarta, Indonesia, at 144, which is considered "unhealthy for sensitive groups" . With an average annual PM2.5 concentration of 99.6 µg/m3, New Delhi's residents are exposed to high levels of pollution on a near-daily basis, according to IQAir.
The standard unit used to measure invisible, airborne particulate matter, toxic gases and chemical pollutants, µg/m3 stands for micrograms per cubic meter. It measures the mass of a pollutant in micrograms within a specific volume of air , according to the U.S. Environmental Protection Agency. Why Is PM2.5 Often the Primary Pollutant? PM2.5 is the most common primary pollutant in air quality reports because it is exceptionally small, persistent and widespread.
It originates from nearly all major pollution sources—vehicles, industrial emissions, wildfires, agricultural burning and household activities—making it a universal marker of poor air quality. Its microscopic size allows PM2.5 to penetrate buildings and reach deep into the lungs and bloodstream, posing both immediate and long-term health risks.
As a result, it frequently appears as the “main pollutant” in AQI reports, since it is more likely than others to exceed safety thresholds and impact large populations. The ranking offers a snapshot of air quality in more than 100 major cities and changes as pollution and weather conditions shift.
It is not a comparison of cities’ annual average pollution, meaning the U.S. cities’ unusually high positions reflected the immediate effects of the wildfire smoke rather than their typical air quality. The National Weather Service said on Friday that persistent wildfire smoke was producing hazardous air quality around Detroit, where an alert remained in effect. Forecasters expect smoke concentrations to begin improving after a change in wind direction.
How Canadian Wildfire Smoke Is Affecting the U.S. Smoke from wildfires in northern Ontario traveled south across the Great Lakes and spread through parts of the Midwest and Northeast, degrading air quality hundreds of miles from the fires. The plume prompted alerts across multiple states and left the New York City skyline obscured by haze. Officials urged people in affected areas to remain indoors or wear high-quality masks outside.
In New York City, outdoor activities were canceled, cooling centers opened and masks were distributed as smoke combined with high temperatures to create potentially dangerous conditions. Conditions were particularly severe around Detroit. The National Weather Service said AQI readings remained between 300 and 500 overnight, within the hazardous category, as weak surface winds allowed smoke to persist near ground level. The agency warned that the smoke would continue to reduce visibility across the region.
Dense-smoke advisories were issued for parts of Lake Huron, Lake St. Clair and the Michigan waters of Lake Erie, where visibility was expected to fall to 1 nautical mile or less. Detroit’s air-quality alert is scheduled to remain in effect through midnight Friday. Forecasters expect conditions around Detroit to begin improving Friday night as winds shift to the southwest and pushed the densest smoke northeast.
However, continued fire activity in Canada meant changing winds could carry additional smoke into the United States. What Mask Should You Wear for Wildfire Smoke? Health experts told Newsweek that they recommend wearing an N95 or KN95 respirator when exposure to wildfire smoke cannot be avoided. The respirators are designed to filter fine airborne particles when worn correctly, unlike looser face coverings.
“A mask helps, but only the right kind," said Dr. Tyler Evans, founder and CEO of Wellness Equity Alliance. “The hazard in wildfire smoke is fine microscopic particulate matter. They are small enough to travel deep into the lungs and enter the bloodstream. A cloth mask or a surgical mask will not stop them.
"What works is a well-fitting N95 or KN95, because those are built to filter these type of tiny particles. Fit also matters. Air leaking around the edges defeats the purpose, so the mask has to seal against the face. For most healthy people, the first line of defense is still limiting time outdoors and keeping indoor air clean.
A mask is what you reach for when you have no choice but to be outside.
" The Public Health Agency of Canada says that well-fitting N95, KN95 and KF94 respirators can reduce exposure to the fine particles in wildfire smoke. The agency advises choosing one that fits closely over the nose, mouth and chin without gaps around its edges. It also advises against wearing a respirator while sleeping. Children younger than 2, people who have difficulty breathing while wearing one and those unable to remove it without assistance should not use a respirator.
Anyone who needs to take one off should first move to an area with cleaner air when possible. Newsweek has covered this in more detail here. Contact Newsweek editors on this story: Matthew Robinson and Dave Siminoff.
Three U.S. cities rose to the top of a global ranking for worst air quality on Friday amid widespread smoke from Detroit recorded a"very unhealthy" U.S. Air Quality Index reading of 240 between 1 and 2 p.m. ET, placing it first among the major cities tracked by Swiss air-quality company IQAir. Chicago followed with an “unhealthy” reading of 199, followed by Washington, D.C. , at 172. New York City placed eighth at 131.
The three worst cities outside the U.S. were Kinshasa, in the Democratic Republic of the Congo, at 186, Delhi, India , at 163, and Jakarta, Indonesia, at 144, which is considered"unhealthy for sensitive groups" . With an average annual PM2.5 concentration of 99.6 µg/m3, New Delhi's residents are exposed to high levels of pollution on a near-daily basis, according to IQAir.
The standard unit used to measure invisible, airborne particulate matter, toxic gases and chemical pollutants, µg/m3 stands for micrograms per cubic meter. It measures the mass of a pollutant in micrograms within a specific volume of air , according to the U.S. Environmental Protection Agency. PM2.5 is the most common primary pollutant in air quality reports because it is exceptionally small, persistent and widespread.
It originates from nearly all major pollution sources—vehicles, industrial emissions, wildfires, agricultural burning and household activities—making it a universal marker of poor air quality. Its microscopic size allows PM2.5 to penetrate buildings and reach deep into the lungs and bloodstream, posing both immediate and long-term health risks.
As a result, it frequently appears as the “main pollutant” in AQI reports, since it is more likely than others to exceed safety thresholds and impact large populations. The ranking offers a snapshot of air quality in more than 100 major cities and changes as pollution and weather conditions shift.
It is not a comparison of cities’ annual average pollution, meaning the U.S. cities’ unusually high positions reflected the immediate effects of the wildfire smoke rather than their typical air quality. The National Weather Service said on Friday that persistent wildfire smoke was producing hazardous air quality around Detroit, where an alert remained in effect.
Forecasters expect smoke concentrations to begin improving after a change in wind direction.traveled south across the Great Lakes and spread through parts of the Midwest and Northeast, degrading air quality hundreds of miles from the fires. The plume prompted alerts across multiple states and left the New York City skyline obscured by haze. Officials urged people in affected areas to remain indoors or wear high-quality masks outside.
In New York City, outdoor activities were canceled, cooling centers opened and masks were distributed as smoke combined with high temperatures to create potentially dangerous conditions. Conditions were particularly severe around Detroit. The National Weather Service said AQI readings remained between 300 and 500 overnight, within the hazardous category, as weak surface winds allowed smoke to persist near ground level. The agency warned that the smoke would continue to reduce visibility across the region.
Dense-smoke advisories were issued for parts of Lake Huron, Lake St. Clair and the Michigan waters of Lake Erie, where visibility was expected to fall to 1 nautical mile or less. Detroit’s air-quality alert is scheduled to remain in effect through midnight Friday. Forecasters expect conditions around Detroit to begin improving Friday night as winds shift to the southwest and pushed the densest smoke northeast.
However, continued fire activity in Canada meant changing winds could carry additional smoke into the United States.that they recommend wearing an N95 or KN95 respirator when exposure to wildfire smoke cannot be avoided. The respirators are designed to filter fine airborne particles when worn correctly, unlike looser face coverings.
“A mask helps, but only the right kind," said Dr. Tyler Evans, founder and CEO of Wellness Equity Alliance. “The hazard in wildfire smoke is fine microscopic particulate matter. They are small enough to travel deep into the lungs and enter the bloodstream. A cloth mask or a surgical mask will not stop them.
"What works is a well-fitting N95 or KN95, because those are built to filter these type of tiny particles. Fit also matters. Air leaking around the edges defeats the purpose, so the mask has to seal against the face. For most healthy people, the first line of defense is still limiting time outdoors and keeping indoor air clean.
A mask is what you reach for when you have no choice but to be outside.
" The Public Health Agency of Canada says that well-fitting N95, KN95 and KF94 respirators can reduce exposure to the fine particles in wildfire smoke. The agency advises choosing one that fits closely over the nose, mouth and chin without gaps around its edges. It also advises against wearing a respirator while sleeping. Children younger than 2, people who have difficulty breathing while wearing one and those unable to remove it without assistance should not use a respirator.
Anyone who needs to take one off should first move to an area with cleaner air when possible.
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