Study Reveals Alarming Levels of Submicron Particulate Matter in U.S. Air

A recent study conducted by researchers at Washington University in St. Louis (WashU) has revealed concerning levels of submicron particulate matter (PM 1) across the United States, emphasizing its potential health hazards. Published in *The Lancet Planetary Health* on June 11, 2025, the study highlights that PM 1 particles, which are smaller than 1 micron in diameter, may pose greater risks to human health compared to their larger counterparts, PM 2.5.

The research, led by Dr. Randall Martin, the Raymond R. Tucker Distinguished Professor of Energy, Environmental, and Chemical Engineering at WashU, analyzed air quality data collected across the contiguous United States over the past 25 years. Dr. Martin stated, "These data offer new information to advance understanding of how to improve air quality and health." The study utilized advanced satellite remote sensing techniques and modeling atmospheric aerosols to quantify the concentration of PM 1, which are primarily emitted from sources such as diesel engines and wildfires, or formed through secondary processes involving sulfur dioxide and nitrogen oxides.

Chi Li, a research assistant professor and the first author of the study, emphasized the importance of these findings for future research. "These estimates will enable further investigation into both the health and environmental effects of submicron particles," Li said. The researchers noted that these tiny particles can bypass the body's natural defenses due to their size, making them particularly dangerous. PM 1 particles are at least six times smaller than red blood cells, which allows them to penetrate deep into the lungs and potentially enter the bloodstream.

The study found that pollution control measures have led to a significant reduction in average PM 1 levels in the air, from 1998 to 2022, largely due to regulations instituted under the Clean Air Act. However, the reduction rate has slowed since 2010, primarily due to increasing wildfire activity. Jay Turner, the James McKelvey Professor of Engineering Education at WashU and co-author of the study, remarked on the past discussions regarding regulating PM 1, which were overshadowed by a focus on PM 2.5 due to the lack of health impact studies. He stated, "This study provides a comprehensive, nationwide dataset to examine PM 1 impacts on health."

As the research progresses, the next step involves collaborating with epidemiologists to assess the health implications associated with PM 1 exposure. The dataset created through this study represents a significant advancement in understanding the prevalence and effects of submicron particulate matter in the United States, an area where previous measurements were scarce. With countries like China already tracking PM 1 levels, the findings position the U.S. to catch up in monitoring this critical pollutant.

In conclusion, the implications of this research extend beyond mere data collection; they signify a call to action for policymakers and public health officials to implement more effective air quality regulations that account for all particulate matter, especially the smaller and potentially more harmful PM 1. Future research will be crucial in determining the full impact of these pollutants on public health and the environment, as well as the efficacy of existing regulatory measures.