A wave of dense smoke originating from Canadian wildfires spread across the northeastern United States and southern Canada on Thursday. This led to an orange sun and air in major cities becoming potentially unsafe to breathe.
On Thursday morning, air quality indices showed alarming levels in cities such as Chicago, Cleveland, Detroit, Minneapolis, and Toronto. Forecasts predicted worsening conditions throughout the day. New York’s Mayor Zohran Mamdani advised over eight million citizens to remain indoors. He stated, “At unhealthy levels, everyone, regardless of health conditions or age, may experience health effects.”
Forecast
The smoke is expected to migrate south from Canada and the Great Lakes region during the day. It could extend as far south as Maryland. Around New York City, the most severe conditions are expected in the afternoon and evening.
Climate Impact
Climate change continues to drive global temperatures past records, increasing the days when air is both hot and polluted.
Health Concerns
Wildfires can result in harmful smoke levels. Protective measures are necessary even if you’re far from the fires.
Outdoor Activity
Deciding to exercise outdoors during smoky conditions requires caution. Protective strategies should be considered if you choose to go outside.
The Air Quality Index (AQI) ranges from 0 to 500. On Thursday, figures exceeded 500 in cities like Milwaukee, Detroit, and Toledo, Ohio. Any AQI above 300 is deemed hazardous. Mayor Mamdani reiterated the importance of reducing outdoor activity and avoiding rigorous exertion.
In Toledo, Ohio, smoke thickened to the extent that visibility of its bridges was severely impaired on Thursday morning. The city recorded one of the nation’s worst air quality levels, making casual observation difficult.
Satellite images captured a wide band of dense smoke from the wildfires stretching from the Upper Midwest and Canada, moving through the Great Lakes, southern Ontario, New England, and reaching New York City.
Worst Air Quality Regions
The worst air quality on Thursday was in Minnesota, Wisconsin, and Ontario, where active wildfires burned. U.S. cities like Minneapolis, Chicago, Milwaukee, Detroit, and Cleveland also faced hazardous conditions. Prospects were grim; forecasts indicated deteriorating air quality throughout the day in places such as Toronto and New York.
Smoke Trajectory
The smoke followed a similar path on Thursday as it did on Wednesday. Predictions suggested southern movement, potentially reaching Maryland. Around New York City, the peak smoke density was anticipated in the afternoon and evening.
Duration
A heat dome affecting the Midwest and Northeast has trapped smoke near ground level. By the weekend, shifting weather systems are expected to reduce both heat and smoke in the Northeast. However, closer to the fire zones, smoke will likely persist.
On Thursday, air quality readings across the affected regions remained disturbingly high. Any AQI over 100 signals warnings to those with respiratory issues. Values above 150 are considered unhealthy, over 200 very unhealthy, and over 300 hazardous.
AQI measures five pollutants: ground-level ozone, particulates, carbon monoxide, nitrogen dioxide, and sulfur dioxide.
In northeastern Minnesota, readings surpassed the 300 mark on Wednesday, indicating “hazardous” conditions.
Toronto hit an AQI close to 400 on Thursday, forecasting hazardous conditions through much of the morning. The city hoped for recovery to healthier levels by Thursday evening. The previous day, Toronto’s AQI was among the worst globally, with U.S. states from Minnesota to Connecticut witnessing unhealthy air quality levels.
By Wednesday night, cities like Minneapolis and Detroit had AQI readings of 287 and 196, respectively. In New York City, the AQI reached 192, while Scranton, Pa., recorded 157.
Additional Insights
Days with both high temperatures and pollution are increasing as a result of climate change. The Times’s Climate team researched several converging factors amplifying health risks during extreme heat.
Options exist for protection against wildfire smoke. The Well team shared guidance on self-protection, even miles from fires.
Whether it is safe to exercise outdoors during smoky conditions calls for careful consideration. The Well guide also covers information necessary for athletes.
Wildfire smoke is worsening air quality in Toronto, as evidenced by video of fires impacting a Canadian cargo train.
Smoke Conditions in Ontario
Ontario’s widespread fires led to evacuations in multiple communities, sending smokey skies over Toronto and beyond. On Wednesday, Toronto awoke to an orange sky, accompanied by acrid wood smoke. Environment Canada issued health warnings about outdoor time in Toronto.
Brian Proctor, a meteorologist, commented on the intense coverage, “We’re really being fumigated.” The southward trajectory of smoke suggests worsening conditions for New York state residents over the next day.
At least six rural and First Nations communities near Thunder Bay, Ontario, evacuated due to fires. Namaygoosisagagun First Nation residents vacated by boat, compelled by safety concerns.
An entire community has disappeared due to the disaster, said Member of Provincial Parliament Sol Mamakwa, expressing solidarity with those affected.
Three cargo trains carrying flammable materials faced threats from nearby fires, prompting holdups by Ontario Provincial Police at safer locations.
Footage from a locomotive passing through Armstrong, Ontario, revealed engineers coordinating with their dispatch team amidst approaching flames. Canadian National Railway confirmed the crew’s safe evacuation, temporarily halting operations for safety.
Municipal measures to restrict open flames, including campfires, followed a hot Tuesday with temperatures up to 37 Celsius in Toronto.
Moist weather minimized the earlier season’s fires, lasting April to October.
Managed by the Canadian Interagency Forest Fire Center, 838 active wildfires spread across the nation, with 4.7 million acres burned so far. This is less than the 22.2 million acres consumed by fires in the second-most destructive year, 2025.
Expected Weather
Heat and haze, caused by a heat dome, engulfed regions from Ontario down to the northeastern U.S. The dome traps smoke from the wildfires at low altitudes.
While Toronto experienced poor air quality unusual for Canada, global comparisons showed similar conditions in Delhi and Dhaka during parts of the year.
Safety Measures Against Wildfire Smoke
Wildfire smoke can create dangerous air quality near fire source areas. Precautionary steps can protect individuals.
Check Air Quality
Online maps track air quality and wildfire smoke patterns across the nation. Platforms like AirNow.Gov provide AQI ratings in various regions, helping assess outdoor time safety.
If the AQI surpasses 100, air may pose risks to vulnerable individuals. CDC highlights possible health issues from AQI levels between 151 and 200, particularly for sensitive groups. An AQI ranging between 301 and 500 can cause adverse health effects across populations.
Assess Personal Risk
Smoke aggravates symptoms of respiratory disorders such as asthma. Extra caution is advised during smoky times for individuals with conditions like COPD, diabetes, or heart issues.
Children and pregnant women may also be sensitive, as CDC warns. Any person can experience wildfire smoke effects, including coughing, irritated eyes, headaches, sore throat, chest pain, rapid heart rate, and fatigue.
Wear a Mask
A high-quality mask, like an N95, offers protection by filtering small smoke particles when venturing outside, suggested Laura Corlin from Tufts University.
Home Precautions
An indoor environment free from smoke is ideal. Dr. Corlin recommends sealing windows and using air purifiers or air conditioners. Central air systems should recirculate air, keeping outdoor smoke away. Fans, albeit less effective, can circulate indoor air at high speed.
Heat-Related Illness Signs
Excessive heat may worsen smoke effects in at-risk individuals and introduce additional health threats. Maintaining hydration is vital. Cooling with water on wrists or neck can help. Signs of heat stroke include body temp over 103 degrees, dizziness, headaches, nausea, confusion, and red skin. Seek urgent medical care for stroke symptoms.
Monitor Health
Become alert for complications from smoke, notably cardiac issues or stroke symptoms, in days following exposure. Special attention to chest pain or increased heart rate during the week after exposure is essential.