Impacts of using auto-mode portable air cleaner on indoor PM_2.5 levels: An intervention study

“Auto-mode” portable air cleaners (PACs) designed to turn on automatically in response to elevated indoor PM_2.5 concentrations are widely used in residences. This study assesses the impacts of using such PACs equipped with high-efficiency particulate air filters on residential PM_2.5 levels in six households recruited in Seattle, Washington, for a randomized crossover study, in which participants used a PAC in their homes under three intervention scenarios: (1) sham-mode filtration in which all filters in the PAC were removed, (2) auto-mode filtration in which the PAC was set to auto mode, and (3) adjustable-mode filtration in which the participants were allowed to manually adjusted the PACs. Each filtration session was one-week long. PM_2.5 levels were measured at 1-min intervals in the kitchen and living room of each household. Also, an hourly time-activity log was collected from each participant. The empirical concentrations and I/O ratios of PM_2.5 were compared among the three filtration modes. Additionally, linear mixed-effects regression models (LMER) were developed to reveal the impacts of different filtration modes on indoor PM_2.5, while controlling for outdoor PM_2.5, indoor cooking events, and indoor relative humidity, and temperature. Based on the LMER models, when indoor cooking events were present and absent, auto-mode filtration significantly reduced the indoor PM_2.5 levels by 31% [95% CI: 19%, 42%] and 28% [95% CI: 22%, 34%], respectively, compared with sham-mode filtration, and reduced the indoor PM_2.5 levels by 19% [95% CI: 6%, 31%] and 4% [95% CI: 4%, 11%], respectively, compared with adjustable-mode filtration. These findings suggest that using such PACs running in auto mode is a practical and effective way to reduce indoor PM_2.5 levels.