WASHINGTON — A new report from the National Academies of Sciences, Engineering, and Medicine recommends public health officials and other local and regional agencies take action to mitigate exposure to fine particulate matter indoors, prioritizing interventions among susceptible populations, including older adults, young children, and individuals with preexisting conditions. It specifically calls for action to reduce exposures to fine particulate matter in schools, including infectious aerosols — a step that research says has the potential to improve students’ health and performance. The report also outlines what is currently known about the health risks of exposure to indoor particulate matter and where more research is needed.

Airborne particulate matter is a mixture of solid particles and liquid droplets. Particulate matter found in buildings can come from outdoor pollution sources (such as vehicle and industrial emissions, wildfire smoke, etc.), from indoor sources like cooking, and building occupants’ respiratory particles, which can contain bacteria and viruses.  

Fine particulate matter has a diameter of 2.5 microns or less — at least 30 times smaller than the diameter of a single human hair — making it small enough to penetrate deeply into the respiratory system and, at its smallest, cross the blood-brain barrier. This can have effects on the respiratory, cardiovascular, and neurological systems. The COVID-19 pandemic increased public awareness of airborne contaminants and highlighted the need for action. However, the report says there is currently a lack of centralized responsibility for dealing with particulate matter indoors, and calls for more unified study and responses. 

Practical mitigation of indoor fine particulate matter is currently possible, the report says. It recommends various mitigation strategies to reduce exposure: controlling sources, improving ventilation when outdoor levels are low, operating filtration-based air cleaning (including stand-alone air cleaners), and where necessary using personal protective equipment.  

“We already have effective mitigation tools available to reduce fine particulate matter exposure indoors — we just need to use them,” said Richard L. Corsi, dean of engineering of the University of California, Davis, and chair of the committee that wrote the report. “There are technical improvements that can be made to reduce exposure and increase the efficiency of filtration systems, but primarily we need more targeted research about indoor particulate matter and urgent and organized action to improve public health.”  

Studies point to the potential for large disparities in fine particulate matter exposure and related health outcomes among populations, the report says. Higher concentrations of indoor fine particulate matter can be associated with outdated appliances that have higher emissions, for example, and ventilation equipment that is not present or is less effective at removing fine particulate matter; and communities that are located closer to pollution sources are more likely to be exposed to outdoor fine particulate matter. These disparities can lead to excessive health burdens on some populations, often economically disadvantaged and marginalized communities.  

“Differences in fine particulate matter exposure are a source of health inequities across communities,” emphasized National Academy of Engineering President John Anderson. “This report highlights how extensive study of indoor environments and engineering innovation can lead to public health improvements, especially among young children and those in marginalized populations.”  

This study was undertaken by the Committee for the Health Risks of Indoor Exposures to Fine Particulate Matter and Practical Mitigation Solutions and sponsored by the U.S. Environmental Protection Agency.  

The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, engineering, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.