Real‐time measurements of PM2.5and ozone to assess the effectiveness of residential indoor air filtration in Shanghai homes

Portable air cleaners are increasingly used in polluted areas in an attempt to reduce human exposure; however, there has been limited work characterizing their effectiveness at reducing exposure. With this in mind, we recruited forty-three children with asthma from suburban Shanghai and deployed air cleaners (with HEPA and activated carbon filters) in their bedrooms. During both 2-week filtration and non-filtration periods, low-cost PM2.5 and O3 air monitors were used to measure pollutants indoors, outdoors, and for personal exposure. Indoor PM2.5 concentrations were reduced substantially with the use of air cleaners, from 34 ± 17 to 10 ± 8 µg/m3 , with roughly 80% of indoor PM2.5 estimated to come from outdoor sources. Personal exposure to PM2.5 was reduced from 40 ± 17 to 25 ± 14 µg/m3 . The more modest reductions in personal exposure and high contribution of outdoor PM2.5 to indoor concentrations highlight the need to reduce outdoor PM2.5 and/or to clean indoor air in multiple locations. Indoor O3 concentrations were generally low (mean = 8±4 ppb), and no significant difference was seen by filtration status. The concentrations of pollutants and the air cleaner effectiveness were highly variable over time and across homes, highlighting the usefulness of real-time air monitors for understanding individual exposure reduction strategies.