Airborne microplastics more concentrated at night, posing greater respiratory risk, study finds

Microplastics floating in urban air are more concentrated at night than during the day, and the vast majority are small enough to enter the human body through the respiratory tract, a new study has found.

The findings suggest that microplastic exposure is not merely an environmental concern but a direct public health risk.

A research team led by Jeon Gi-jun, a professor in the Department of Environmental Engineering at Inha University, and Yu Han-jin, a researcher at the Greater Seoul Particulate Matter Research and Management Center, analyzed daytime and nighttime air samples collected in Incheon. The team announced Monday that airborne microplastic concentrations averaged about 1,300 particles per cubic meter, with nighttime levels running roughly 60% higher than daytime levels.

Among the study's most notable findings was the size of the detected particles. About 95 percent measured 10 micrometers or smaller — fine enough to be inhaled into the human respiratory tract.

Of those, about 40 percent were classified as ultrafine particles comparable in size to PM2.5 fine dust.

That means microplastics inhaled during ordinary breathing could penetrate deep into the lungs.

The results add to a growing body of international research that has detected microplastics in human blood, lung tissue and placentas, reinforcing concerns about the health effects of airborne microplastic exposure.

The research team particularly highlighted nighttime as the more dangerous period.

At night, the atmospheric mixing layer drops and air circulation slows, causing pollutants to linger near the surface for longer periods.

As a result, microplastic concentrations rise at night in much the same way fine dust levels do, the researchers said.

The study also identified "resuspension" as a major source of airborne microplastics — a process in which particles that have accumulated on roads, soil and in the ocean are lifted back into the air by vehicle traffic or wind, rather than coming solely from the direct breakdown of plastic products.

"We confirmed that atmospheric microplastic concentrations can vary significantly depending on weather conditions," Yu said. "Long-term monitoring linked to fine dust research and identification of emission sources are needed."

Jeon said atmospheric microplastics represent "a new form of air pollutant for which no environmental standards or management framework yet exists," adding that concentration monitoring, health impact assessments and the development of standardized analytical methods are urgently needed.

The research was supported by the Ministry of Environment, Incheon city and the National Research Foundation of Korea, and the findings were published in the international environmental science journal Environment International.

The research team plans to conduct joint observations with public health and environmental research institutes across the country this year to map the regional distribution and emission characteristics of airborne microplastics nationwide.