Air pollution kills approximately 50,000 people in the United States each year, but not all pollutants are equally harmful. Although PM2.5 (particulate matter with a diameter of less than 2.5 microns) pollution has been studied for a long time, the health effects of the smaller PM1 (with a diameter of less than 1 micron) have not been fully understood.
In the latest study published in The Lancet Planetary Health, a research team from the University of Washington quantified PM1 pollution levels in the United States over the past 25 years for the first time. The study calculated the national PM1 concentration in the United States through modeling based on the seven main components of PM2.5 (such as sulfate, nitrate and mineral dust). This data provides an important basis for future health and environmental research.
PM1 mainly originates from direct emissions, such as black carbon particles from diesel engines and wildfire smoke, and sometimes may be formed through secondary reactions of sulfur dioxide and nitrogen oxides emitted by fuel combustion. Due to the tiny size of PM1 (less than one-sixth of a blood cell), they can penetrate deeper into the human body and cause greater harm.
The study found that between 1998 and 2022, PM1 levels in the United States dropped significantly due to environmental policies such as the Clean Air Act, but the improvement slowed down after 2010, mainly due to increased wildfire activity. Future pollution prevention and control must pay attention to emerging non-fossil fuel pollution sources.
Currently, other countries such as China are one step ahead in tracking PM1 nationwide.
This study fills a gap in this area in the United States and provides critical data for policy development and health risk assessment. Next, the researchers plan to work with epidemiologists to further analyze the association between PM1 and health problems.