Air contamination leads to health issues and is linked to approximately 50,000 deaths annually in the United States, but not all air pollutants have the same impact.
Researchers have monitored the extent of “PM 2.5” pollution for decades. PM 2.5 refers to particulate matter measuring less than 2.5 microns in width. However, there has been less research conducted on its even smaller counterpart, known as “submicron” or “PM 1” particulate matter, which is below 1 micron in diameter. Why is this significant? Because these “tiny particles” could result in more severe health repercussions.
In a newly published study in The Lancet Planetary Health, scientists at Washington University in St. Louis have measured the levels of PM 1 throughout the United States over the last 25 years.
“These findings provide fresh insights to enhance our understanding of how to improve air quality and public health,” indicated Randall Martin, the Raymond R. Tucker Distinguished Professor of energy, environmental, and chemical engineering at the McKelvey School of Engineering. “This initiative builds upon WashU’s expertise in satellite remote sensing and atmospheric aerosol modeling used in this research,” he added.
Chi Li, a research assistant professor in Martin’s atmospheric composition analysis group, is the leading author of the study. Li explained that these estimates will facilitate further exploration into the health and environmental impacts of submicron particles.
Li noted that the exceedingly small particles identified in this research typically originate from direct emissions, such as black carbon particles produced by diesel engines or smoke from wildfires. Occasionally, PM 1 can also be generated through secondary processes when sulfur dioxide or nitrogen oxides are emitted from fuel combustion or coal burning.
It logically follows that smaller air pollution particles could cause greater harm to the human body as they can bypass the body’s natural defenses. These submicron particles are at least six times smaller than blood cells.
Airborne particles often consist of multiple materials combined together.
According to Li, larger particles are primarily comprised of less modifiable substances, like mineral dust.
The researchers estimated the levels of submicron particles based on known ratios of components that form PM 2.5, which includes seven primary elements such as sulfate, nitrate, and mineral dust.
“By combining these seven constituents, we can derive the overall PM 1 concentration across the country,” Li explained.
This research lays the groundwork for further exploration into the locations, methods, and reasons certain types of particles gather, as well as their potential impacts on both the environment and human health.
“When the EPA first established a fine PM air quality standard in 1997, there was significant discussion surrounding the regulation of PM 1 or PM 2.5,” noted Jay Turner, the James McKelvey Professor of Engineering Education and co-author of the study. “For various reasons, including the limited health impact studies on PM 1 compared to those on PM 2.5, the latter was selected. This study offers a comprehensive, nationwide dataset to explore the health effects of PM 1.”
The next phase will involve collaboration with epidemiologists to evaluate the correlation between PM 1 and health outcomes.
The new dataset unveiled another significant insight: pollution regulation is beneficial. In the contiguous United States, average PM 1 levels in the air dropped significantly from 1998 to 2022, largely due to decades of environmental policies like the Clean Air Act. However, this progress has decelerated since 2010, primarily due to increasing wildfire activity. Future pollution regulations will need to tackle new, non-fossil fuel sources, according to the study authors.
Countries like China have made progress in monitoring nationwide PM 1 levels, but the U.S. is poised to catch up quickly.
“This dataset provides unparalleled information for the United States regarding a crucial pollutant for which there are few other measurements,” said Martin.
Li C, Martin RV, van Donkelaar A, Jimenez JL, Zhang Q, Turner JR, Liu X, Rowe M, Meng J, Yu W, Thurston, GD. Estimates of submicron particulate matter (PM1) concentrations for 1998-2022 across the contiguous United States. Lancet Planetary Health. Online June 11, 2025. DOI: http://10.1016/S2542-5196(25)00094-4
Funding from the National Institute of Environmental Health Sciences, part of the National Institutes of Health (NIH).
Originally published on the McKelvey Engineering website
The article Tiny and toxic: Researchers track smaller air pollution particles across US skies was first featured on The Source.