Air pollution remains a significant health crisis in the United States, contributing to approximately 50,000 deaths annually. While the dangers of PM 2.5, particulate matter less than 2.5 microns in diameter, have been well-documented, a new study sheds light on an even smaller particle, PM 1, which measures less than 1 micron in diameter and may pose more severe health risks.
Researchers at Washington University in St. Louis have quantified the levels of PM 1 across the U.S. over the last 25 years in a study published in The Lancet Planetary Health. Randall Martin, the Raymond R. Tucker Distinguished Professor of energy, environmental, and chemical engineering at the McKelvey School of Engineering, expresses the significance of the research, stating, “These data offer new information to advance understanding of how to improve air quality and health.”
The first author of the study, Chi Li, a research assistant professor, explained that the estimates generated will facilitate deeper investigations into the health and environmental impacts of submicron particles. PM 1 particles primarily originate from direct air emissions, such as black carbon particles emitted by diesel engines or smoke produced by wildfires. Additionally, PM 1 can form through secondary processes when sulfur dioxide or nitrogen oxides are released during fuel combustion or coal burning.
Given their incredibly small size, PM 1 particles can infiltrate the human body more easily than larger particles. According to Li, these particles are at least six times smaller than blood cells, increasing their potential to bypass the body’s natural defenses.
The study underscores the complexity of air pollution; particles are typically a mixture of various materials rather than being a single entity. Larger particles tend to comprise more stable components, such as mineral dust, whose levels are harder to modulate.
Using established ratios of the components that compose PM 2.5, including sulfates, nitrates, and mineral dust, the researchers calculated the total PM 1 concentration across the country. Li noted that this approach allowed for a comprehensive understanding of PM 1 pollution levels and sets a foundation for future investigations into the geographical and environmental factors influencing these particles’ accumulation, as well as their effects on human health.
Jay Turner, the James McKelvey Professor of Engineering Education and co-author of the study, highlighted that PM 1 was originally considered for regulation when the Environmental Protection Agency (EPA) established the PM air quality standard in 1997. However, due to a scarcity of health impact studies specifically concerning PM 1, focus shifted toward regulating PM 2.5. Turner emphasizes the importance of this study, which provides a nationwide dataset that enables researchers to explore the health impacts associated with PM 1.
The fresh dataset also revealed a notable trend: pollution regulation has been effective. Between 1998 and 2022, average PM 1 levels in the contiguous U.S. experienced a significant decline, largely attributed to stringent environmental regulations such as the Clean Air Act. However, progress has slowed since 2010, primarily due to an increase in wildfire activity, demonstrating that future pollution control measures must also target non-fossil fuel sources.
Although countries like China have been tracking PM 1 pollution for some time, this new study equips the U.S. with critical data needed to catch up. “This dataset offers unprecedented information for the United States about an important pollutant for which few other measurements exist,” Martin remarked.
With this foundational dataset now available, future research will delve into the correlation between PM 1 exposure and various health outcomes, as researchers collaborate with epidemiologists to interpret the findings.
In summary, the study conducted by Washington University not only enriches our understanding of PM 1 pollution across the U.S. over the past 25 years but also highlights the ongoing challenges and opportunities in improving air quality and public health as environmental conditions evolve.
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