Aerosols—solid or liquid particles in the air that are smaller than the width of a human hair—are everywhere in our environment. Examples of aerosol particles outdoors include smoke, dust, smog, and mist from the ocean. In crowded indoor environments, aerosol particles are emitted by people when they speak, exhale, sing, sneeze, and laugh. If people are infected with a respiratory virus like SARS-CoV-2, the virus can hitch a ride on exhaled aerosol particles, and then infect others via inhalation. The CDC suggests that universal mask wearing, vaccination, and enhanced ventilation in indoor spaces can minimize airborne virus transmission and prevent diseases like COVID-19.

One way to increase ventilation is with portable high efficiency particle air (HEPA) cleaners. HEPA cleaners contain filters that efficiently remove particles via collision of the particle with the filter. Dr. William Lindsley and other CDC scientists investigated if portable high efficiency particle air (HEPA) cleaners and universal masking can significantly reduce exposure to aerosol particles indoors. They placed HEPA cleaners and either unmasked or masked (three-ply cotton) mannequins in a room with one of the mannequins exhaling aerosol particles. The team found that the aerosol exposure decreased by 65% when using only HEPA cleaners in the center of the room near the source mannequin. With only masking, the aerosol exposure decreased by 72%. However, with both HEPA cleaners and masking, the aerosol exposure decreased by 90%.      

Placing HEPA cleaners in areas like schools, offices, and homes can potentially reduce airborne virus transmission and fatalities. Additionally, using HEPA cleaners indoors can likely provide additional protection against SARS-CoV-2 variants. While studies in different indoor environments and those that study infection rates are warranted, Dr. Lindsley and other CDC scientists show that portable HEPA cleaners along with masking can help in the fight against COVID-19.     

Dr. William G. Lindsley is a research biomedical engineer in the Health Effects Laboratory Division of the National Institute for Occupational Safety and Health at the CDC.

Managing Correspondent: Joshua L. Cox

Original Journal Article: “Efficacy of Portable Air Cleaners and Masking for Reducing Indoor Exposure to Simulated Exhaled SARS-CoV-2 Aerosols – United States, 2021” Morbidity and Mortality Weekly Report

Press Articles: “HEPA air cleaners and face masks can reduce the exposure to Covid-infected particles in a room by up to 90%, CDC report finds” DailyMail.com

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