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Scientists track 25 years of submicron air pollution particles across US skies
Air pollution is a serious and often underestimated health threat in the U.S. It is linked to over 50,000 premature deaths each year. Tiny particles in the air, like PM2.5, can get embedded into a person's lungs and bloodstream, leading to chronic heart and lung problems.
PM2.5 refers to particulate matter that is smaller than 2.5 micron. While scientists have studied these particles for decades, far less is known about PM1— even smaller at under 1 micron—whose effect on human health could be equally lethal, if not more.
A new study from Washington University in St. Louis, published in The Lancet Planetary Health, has mapped 25 years of PM1 air pollution across the United States. The findings offer a starting point for identifying which pollutants regulators should target to improve public health. The research also builds on the university's expertise in satellite sensing and atmospheric modeling.
According to Chi Li, research assistant professor at the university's Atmospheric Composition Analysis Group and lead author of the study, the new estimates will help researchers better understand the impact of submicron particles.
These tiny particles often come from direct emissions, like black carbon from diesel engines or smoke from wildfires. They can also form indirectly when pollutants such as sulfur dioxide or nitrogen oxides are released from fuel combustion and coal burning.
Rather than being made of a single substance, air particles are usually mixtures of various materials layered together. Li noted that larger particles are often dominated by components like mineral dust, which are more difficult to regulate or reduce.
The researchers estimated PM1 levels by analyzing the known composition of PM2.5 particles, which include seven main components such as sulfate, nitrate, and mineral dust. By combining these elements, the team was able to calculate PM1 concentrations across the US.
The study lays the groundwork for deeper analysis of where these tiny particles tend to concentrate, how they form, and what impacts they have on both human health and the environment.
PM1 pollution particles may be more harmful because they can penetrate deeper into the body, slipping past natural defenses. These submicron particles are at least six times smaller than a blood cell.
According to Jay Turner, the James McKelvey Professor of Engineering Education and co-author of the study, when the United States Environmental Protection Agency (EPA) first set air quality standards for fine particulate matter in 1997, there was significant debate over whether to regulate PM1 or PM2.5. Due to limited health impact research on PM1 compared to PM2.5, the EPA chose to focus on PM2.5.
However, the new dataset revealed encouraging insights: pollution regulation has significantly reduced PM1 levels across the contiguous U.S. from 1998 to 2022, largely due to environmental policies like the Clean Air Act. But this progress has slowed since 2010, mainly because of increasing wildfire activity.
Although countries like China have gotten a head start in tracking PM1, U.S. can catch up with the help of this comprehensive nationwide dataset. The next step will entail collaboration with epidemiologists to assess how exposure to these tiny particles relates to various health outcomes.
