Efficacy of Portable Air Cleaners and Masking for Reducing Indoor Exposure to Simulated Exhaled SARS-CoV-2 Aerosols — United States, 2021

Updated May 30, 2023

February 2022
NIOSH Dataset RD-1031-2022-0


SARS-CoV-2 can be spread by droplets and aerosols expelled by infected people when they cough, talk, sing, or exhale. To reduce exposure to these droplets and aerosols while indoors, CDC recommends measures including physical distancing, universal mask wearing, and room ventilation. Ventilation systems can be supplemented with portable air cleaners to remove infectious material from the air more quickly and provide greater protection. We conducted a case study using respiratory simulators to examine the efficacy of portable High Efficiency Particulate Air (HEPA) air cleaners and universal masking at reducing exposure to simulated exhaled aerosol particles from an infected meeting participant in a conference room. We found that, in a room with good air mixing, the use of two HEPA air cleaners meeting the EPA recommended Clean Air Delivery Rate (CADR) reduced the overall exposure by up to 65%, and that the combination of the HEPA air cleaners and universal masking reduced exposure by up to 90%. The air cleaners were most effective when they were close to the aerosol source. Our results demonstrate that portable HEPA cleaners can be an effective method to reduce exposure to airborne particles while meeting indoors, especially in combination with universal masking.

Data Collection Methods

  • A respiratory aerosol simulator (source) and three breathing simulator (recipient) were placed in a conference room.
  • HEPA air cleaners were placed at different locations in the room.
  • Aerosols were exhaled into the room by the respiratory aerosol simulator.
  • Simulators were tested with and without face masks.
  • Aerosol concentrations for 0.3 to 3 µm particles were measured using aerosol optical particle counters.

Publications Based on Dataset

William G. Lindsley, Raymond C. Derk, Jayme Coyle, Stephen B. Martin, Jr., Kenneth R. Mead, Francoise M. Blachere, Donald H. Beezhold, John T. Brooks, Theresa Boots, and John D. Noti (2021). Efficacy of portable HEPA air cleaners for reducing exposure to simulated exhaled aerosols in indoor meeting rooms. MMWR Morbidity and Mortality Weekly Report 70(27):972-976.


This project was supported by the National Institute for Occupational Safety and Health (NIOSH). When a publication makes use of this dataset, acknowledgement of the development of the dataset should be attributed to the NIOSH Health Effects Laboratory Division.

We would like to recognize the work of William G. Lindsley1, Raymond C. Derk1, Jayme Coyle1, Stephen B. Martin Jr2, Kenneth R. Mead3, Francoise M. Blanchere1, Donald H. Beezhold1, John T. Brooks4, Theresa Boots1, and John D. Noti1.

1 National Institute for Occupational Safety and Health, Health Effects Laboratory Division
2 National Institute for Occupational Safety and Health, Respiratory Health Division
3National institute for Occupational Safety and Health, Division of Field Studies and Engineering
4National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Division of HIV Prevention


NIOSH/Health Effects Laboratory Division
Allergy and Clinical Immunology Branch
(304) 285-6024