Smoke drifting south from wildfires burning in Canada has settled over much of the United States, pushing air quality to unhealthy levels across roughly 20 states and prompting warnings for residents to limit time outdoors.

The haze has reached from the Upper Midwest to the East Coast, dimming skies over major cities and leaving the air thick enough to see. In New York, monitors registered readings in the range health officials label unhealthy, the point at which sensitive groups and, in some cases, the general public are advised to take precautions. Washington and other cities along the corridor recorded similar conditions.

Minnesota has been among the states most affected. Officials there declared a state of emergency and issued an air quality alert as smoke thickened over the region. Across the border, the fires have forced thousands of people to evacuate their homes, and the plumes those blazes generate have carried the pollution hundreds of miles.

The smoke arrived alongside a stretch of high temperatures in the Northeast. New York and Washington faced peak heat as the Canadian smoke spread, a combination that compounds the strain on people with respiratory or heart conditions. Heat and poor air quality each carry health risks on their own; together they raise the concern for older adults, children, and those with existing illnesses.

The pollutant of primary concern in wildfire smoke is fine particulate matter, the microscopic particles small enough to travel deep into the lungs and enter the bloodstream. Air quality is tracked through the Air Quality Index, a scale that moves from green at the healthiest end through yellow, orange, and red as conditions worsen. A "red" reading signals air considered unhealthy for the broader population, not only sensitive groups.

Health authorities have offered consistent guidance as the smoke lingers. Residents in affected areas are advised to stay indoors when possible, keep windows closed, run air filtration where available, and avoid strenuous outdoor activity. Those who must be outside are encouraged to monitor local readings, which can shift quickly with the wind.

How long the current episode persists will depend on the behavior of the fires and on weather patterns that determine whether the smoke stalls over populated areas or clears out.

For now, forecasters and health officials are urging people in the affected states to check air quality readings in their own communities before heading outdoors, as conditions vary from city to city and hour to hour.

References

1. 1.Bloomberg — New York and Washington facing peak heat as Canadian smoke spread
2. 2.Air quality monitoring reports — roughly 20 states affected; NYC 'red' unhealthy readings
3. 3.Minnesota state officials — state of emergency and air quality alert
4. 4.Canadian wildfire reports — thousands evacuated