Wildfire smoke pushes air quality to dangerous levels for millions

By JUDSON JONES, NICHOLAS BOGEL-BURROUGHS, DANI BLUM and SALLY GOLDENBERG

A plume of dense smoke from scores of raging wildfires stretched across much of the northeastern United States and southern Canada on Thursday, prompting officials and health experts in some of the region’s most populated cities to urge residents to avoid spending too much time in the polluted air.

Air quality readings in Chicago, Cleveland, Detroit, Minneapolis and Toronto surged to levels so dangerous that one public health expert said “nobody should spend time outside.” Conditions were forecast to worsen throughout the day as skylines and tall buildings disappeared from view under a suffocating haze, and dozens of wildfires continued to burn.

By midday, sensors in the Upper Midwest and southern Ontario, where the smoke was at its most dense, were recording the worst air quality in North America. Readings in Washington, Philadelphia and New York City were all at unhealthy levels.

Mayor Zohran Mamdani of New York urged the 8 million residents of the nation’s largest city to stay indoors. “At unhealthy levels, everyone — not just people with asthma and heart conditions, not just older adults — everyone may feel health effects,” he said.

Here’s what we’re covering:

— Air quality: Air is considered hazardous when the quality index — which measures the density of five pollutants — tops 300. On Thursday, Toledo, Ohio; Milwaukee and Detroit were among the places with AQI levels over 500.

— Canadian evacuations: In Ontario, where roughly 135 active wildfires were burning Wednesday night, officials were bracing for a potential escalation and widespread community evacuations.

— Political threats: Republican lawmakers from states affected by the smoke threatened punitive action against Canada, accusing the country of mismanaging the wildfires. Sen. Bernie Moreno, R-Ohio, said he would introduce a bill next week to penalize Canada “for this atrocity.”

— The forecast: The densest smoke is expected to move south throughout the day, potentially dipping as far south as Maryland. Around New York City, the worst conditions were expected in the afternoon and evening.

— Climate impact: As climate change drives global temperatures past record levels, the frequency of days when the air is both hot and polluted has been increasing.