Reductions in particulate matter concentrations resulting from air filtration: A randomized sham-controlled crossover study

Deborah H. Bennett, Rebecca E. Moran, Paula Krakowiak, Daniel J. Tancredi, Nicholas J. Kenyon, Jeffery Williams, William J. Fisk

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


One-hundred seventy-two households were recruited from regions with high outdoor air pollution (Fresno and Riverside, CA) to participate in a randomized, sham-controlled, cross-over study to determine the effectiveness of high-efficiency air filtration to reduce indoor particle exposures. In 129 households, stand-alone HEPA air cleaners were placed in a bedroom and in the main living area. In 43 households, high-efficiency MERV 16 filters were installed in central forced-air heating and cooling systems and the participating households were asked to run the system on a clean-air cycle for 15 min per hour. Participating households that completed the study received true air filtration for a year and sham air filtration for a year. Air pollution samples were collected at approximately 6-month intervals, with two measurements in each of the sham and true filtration periods. One week indoor and outdoor time-integrated samples were collected for measurement of PM2.5, PM10, and ultrafine particulate matter (UFP) measured as PM0.2. Reflectance measurements were also made on the PM2.5 filters to estimate black carbon. True filtration significantly improved indoor air quality, with a 48% reduction in the geometric mean indoor PM0.2 and PM2.5 concentrations, and a 31% reduction in PM10. Geometric mean concentrations of indoor/outdoor reflectance values, indicating fraction of particles of outdoor origin remaining indoors, decreased by 77%. Improvements in particle concentrations were greater with continuously operating stand-alone air cleaners than with intermittent central system filtration. Keeping windows closed and increased utilization of the filtration systems further improved indoor air quality.

Original languageEnglish (US)
Article numbere12982
JournalIndoor Air
Issue number2
StatePublished - Feb 2022


  • central system filtration
  • indoor air quality
  • PM
  • stand-alone air cleaners
  • ultrafine particles

ASJC Scopus subject areas

  • Environmental Engineering
  • Building and Construction
  • Public Health, Environmental and Occupational Health


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