Air pollution is a significant health concern in the United States, leading to approximately 50,000 deaths annually. However, not all air pollutants are created equal.

Scientists have long studied the impact of 'PM 2.5' pollution, which consists of particulate matter less than 2.5 microns in diameter. But the smaller 'submicron' or 'PM 1' particles, less than 1 micron in diameter, have received less attention. These tiny particles could potentially pose greater health risks.

Researchers at Washington University in St. Louis recently published a study in The Lancet Planetary Health, detailing the concentration of PM 1 particles over the US for the past 25 years.

Randall Martin, a professor at WashU, emphasized the importance of this research in identifying pollutants that could have the most significant impact on public health. The study leveraged the university's expertise in satellite remote sensing and aerosol modeling.

Chi Li, the lead author of the study, highlighted that PM 1 particles primarily come from direct air emissions like black carbon from diesel engines and wildfire smoke. These particles can also form through secondary processes involving sulfur dioxide and nitrogen oxides.

Due to their small size, submicron particles can bypass the body's defenses, making them potentially more harmful. The research showed that PM 1 levels have decreased across the US since 1998, thanks to environmental regulations like the Clean Air Act. However, the decline has slowed in recent years due to increased wildfire activity.

The study's findings will aid in understanding how different particles accumulate, their environmental impact, and their effects on human health. Future research will focus on assessing the health outcomes associated with PM 1 exposure.