Smoke from more than 900 active wildfires in Canada caused widespread airspace disruptions in the United States on July 17, 2026, delaying over 10,700 American flights. This marked the sixth consecutive day of hazardous air spreading across the US Midwest, Great Lakes, and East Coast. Over 100 million residents in 18 states were exposed to dangerous concentrations of PM2.5 fine particulate matter due to the thick wildfire smoke.
United Airlines issued an air quality travel advisory on July 17 covering 17 airports in the US and Canada, including Detroit, Toronto Pearson, Buffalo, and Syracuse. Its waiver policy allowed passengers with
tickets purchased by July 16 to rebook flights scheduled for July 17 or 18 with no change fee or fare difference through July 20, provided they remain in the same cabin on the same city pair. This waiver window closes on Monday, July 20.
Delta Air Lines implemented a Midwest Air Quality Advisory for flights between July 16 and 18. The advisory affected cities such as Detroit, Minneapolis-St. Paul, Milwaukee, Green Bay, Grand Rapids, and Madison. Delta passengers could rebook at no cost for travel through July 21. American Airlines, which experienced 42% of its flights delayed on July 17,
more than double its 2026 average of 20%, issued waivers for no-cost changes until July 18. Passengers who missed the waiver deadline may still apply their ticket’s unused value toward future travel within one year.
The Federal Aviation Administration (FAA) applied a ground delay program affecting Philadelphia International Airport on July 16 and 17. The program caused 365 delays and 12 cancellations on July 16, with over 200 delays continuing on July 17. Philadelphia joined major hubs such as Chicago O’Hare and Detroit in experiencing significant delays linked to wildfire smoke’s impact on visibility and airspace management.
Air Quality Conditions and Forecasts
On the morning
of July 19, a third wave of smoke moved into the Great Lakes region, impacting cities like Chicago, Detroit, and parts of the Northeast. Chicago’s Air Quality Index (AQI) reached approximately 153 at 6 a.m., placing it among the world’s worst-polluted major cities at that time, according to IQAir data.
Peak particulate matter readings during the previous days were extreme. Northern Minnesota recorded PM2.5 levels exceeding 600 micrograms per cubic meter on July 16 and 17, surpassing the Environmental Protection Agency’s (EPA) hazardous AQI ceiling of 500. Detroit logged an all-time city record AQI of approximately 600 on July 16,
exceeding New York City’s 465 value from the 2023 wildfire episode. Multiple cities, including Milwaukee, Pittsburgh, and Washington, ranked globally for the worst air quality at various points on July 17.
The EPA advises that AQI readings above 150 require all individuals to limit outdoor exertion; levels above 200 warrant avoiding outdoor activity entirely. Attendees at large outdoor events such as the FIFA World Cup Final at MetLife Stadium in East Rutherford, New Jersey, faced these challenging conditions, although FIFA reported no immediate threat to the final as of July 17.
Political and Legal Developments
On July 17, US President Donald Trump threatened to
add the “incalculable” cost of Canadian wildfire smoke pollution to existing tariffs on Canada. He labeled Canadian fire management as “Willful Negligence” and indicated plans to contact Canadian Prime Minister Mark Carney. Trump stated the cost “must of necessity be added to the TARIFFS Canada is currently paying.”
Legal experts and reports indicate no clear authority for Trump to impose tariffs based on smoke pollution. The Supreme Court ruled on February 20, 2026, that the International Emergency Economic Powers Act does not authorize tariff imposition, and the existing 10% global tariff under Section 122 of the Trade Act is set
to expire on July 24, 2026. Section 301 powers, under consideration, require a finding of discriminatory trade practices, which wildfire events do not constitute. Most Canadian goods under the Canada-United States-Mexico Agreement (CUSMA) are exempt from current tariffs, while US Trade Representative Jamieson Greer declined to renew CUSMA as of July 1, 2026, introducing trade uncertainty.
Canadian Prime Minister Mark Carney emphasized that addressing climate change is “the responsibility of all countries, including the United States,” highlighting US withdrawal from international climate initiatives since Trump’s second term began. Canada’s Emergency Management Minister Eleanor Olszewski confirmed the government has invested $12
billion in forest sustainability and fire prevention since 2020. The bilateral wildfire cooperation agreements signed in 1982 and reaffirmed in 2025 were cited in defense of Canada’s fire management efforts.
Ontario Premier Doug Ford criticized the US administration for blaming Canada, stating, “I find it a shame the administration in the US and Congress people are writing these letters and blaming us.” He challenged the US to lift softwood lumber tariffs exceeding 45%, including a 10% increase imposed in October 2025, especially given Canada’s previous assistance fighting California wildfires.
Scientific Causes and Research Challenges
The wildfires were sparked by a record-breaking heat wave in North
America. On July 13, 2026, temperatures in Ontario rose 25.2 degrees Fahrenheit above average, according to Climate Central. Chief Meteorologist Shel Winkley stated, “These temperatures would be virtually impossible to occur on July 13 in Ontario without the influence of climate change.” Researcher Daniel Swain from the California Institute for Water Resources noted the heat wave dried forests and enabled widespread lightning-induced ignition.
The National Interagency Fire Center reported that more than 5,740 square miles burned in the US during 2026, 31% above the ten-year average through mid-July. Canada’s wildfire season is 134% of its ten-year average through mid-July but
has not reached 2023’s record season levels.
Meanwhile, the Trump administration has listed the Pacific Wildland Fire Sciences Lab in Seattle, critical for wildfire smoke research and the Fire and Smoke Map used by government agencies and firefighting teams, among facilities slated for closure under a reorganization plan. This lab is one of 56 of 90 Forest Service research stations targeted for shutdown.
