The skies above the northeastern US were apocalyptic during the summer of 2023. The smoke from record-breaking wildfires throughout Canada caused catastrophic air quality and even led to unprecedented cooling in the New York and New Jersey metropolitan areas, according to a newly published study.
Researchers from New Jersey’s Rutgers University found the smoke caused “global dimming,” or the decline in sunlight reaching Earth’s surface, in the cities. The effect dropped the region’s temperatures by 3 degrees Celsuius, or 5.4 degrees Fahrenheit.
The temperature drop also trapped air pollutants near ground level. Smoke particles and other particulate matter from the wildfires absorbed and scattered the sun’s light over the cities. The “smoky umbrella” blocked solar radiation and cooled the areas below, limiting natural air circulation and increasing exposure to harmful airborne contaminants.
“This study documents for the first time the effect of wildfire nanoparticles on the microclimate of megacities,” Philip Demokritou, the study’s senior author and professor of nanoscience and environmental bioengineering at Rutgers, said in a press release. “Such ambient air temperature reductions may exacerbate the urban heat island effect and limit the natural ventilation of megacities, exacerbating the exposure to air pollution.”

The total particulate matter in New York City’s skies was more than three times higher than the Environmental Protection Agency’s guidelines, and eight times higher than the World Health Organization’s recommendation, researchers said. The air pollution reportedly contributed to health impacts across the region, according to epidemiological studies in the cities that showed increases in emergency hospital visits and the exacerbation of asthma.
A companion paper from the same research team also found that 9.2 mg of smoke particles were deposited in people’s lungs in the region during the event. The particles reduced the viability of immune cells in people’s lungs, increasing vulnerability to respiratory infections.
“Wildfire events have increased in frequency and intensity dramatically due to extreme drought and heat and now affect even the Northeast U.S.,” Demokritou said. “This was the first event of this scale in the region, but it probably won’t be the last.”