South Middlesex Times

When Canadian wildfire smoke enveloped New York City in June 2023, turning the skies an orange hue, it led to severe air quality issues and an unexpected cooling of the region by approximately 3 degrees Celsius. This cooling effect, described as "global dimming," trapped pollutants close to the ground, according to researchers from Rutgers Health who published their findings in Nature's Communications Earth & Environment.

Philip Demokritou, senior study author and Henry Rutgers chair and professor at Rutgers School of Public Health and School of Engineering, commented on this discovery, saying, "With all you hear about the negative consequences of global warming, you might think the cooling would be good. But cooler temperatures are equally bad as global warming. This effect on microclimate can disrupt the hydrological cycle, trap other toxic air compounds and increase human exposure levels."

The researchers focused on analyzing the physicochemical properties of particulate matter during the peak period of the Canadian wildfires, particularly their light absorption and scattering abilities. The team found that the smoke particles traveled nearly 1,000 kilometers and resulted in an unprecedented radiative forcing of -352.4 watts per square meter at ground level. Georgios Kelesidis, an assistant professor at Rutgers School of Public Health and lead author of the study, noted, “The wildfire particulate matter that arrived in the New Jersey and New York City area on June 7 contained mostly brown carbon particles that had not been photobleached completely despite covering a distance of about 800 kilometers.”

The cooling occurred as wildfire smoke, predominantly composed of organic carbon particles, scattered sunlight away from the Earth's surface, cooling the areas beneath like a smoky umbrella. However, this layer of particles reduced air circulation, preventing pollution dilution and vertical mixing, thus trapping pollutants near the surface and potentially increasing exposure to harmful airborne substances.

Demokritou emphasized, "This study documents for the first time the effect of wildfire nanoparticles on the microclimate of megacities."

During the event, New York City experienced very high levels of particulate matter. Recordings showed particles less than 2.5 micrometers were more than three times Environmental Protection Agency limits and eight times World Health Organization recommendations, contributing to increased health impacts. According to Demokritou, recent epidemiological studies parallel these findings with increased hospital visits and aggravated respiratory conditions.

Additional research from the Rutgers team, published in Environmental Science & Technology, indicated exposure to smoke particles impaired human lung immune defenses significantly. The study discovered that inhaled particles reduced lung macrophages' viability and their ability to neutralize foreign entities, elevating the vulnerability to respiratory infections.

Three epidemiological studies in New York City confirmed increased asthma-related emergencies, with emergency department visits rising by 44% to 82% at the event’s peak.

Demokritou concluded that these circumstances, propelled by climate change and more frequent wildfires, underline the complex interactions between wildfire emissions, urban climates, and public health. "Wildfire events have increased in frequency and intensity dramatically due to extreme drought and heat and now affect even the Northeast U.S.," Demokritou stated. “This was the first event of this scale in the region, but it probably won’t be the last.”