Evaluating Air Pollutant Exposure and the Impacts of Indoor Air Filtration Using Low-Cost Monitors

In highly polluted cities, many residents seek to reduce their personal exposure to air pollutants. However, over the course of a day, people spend time in a variety of micro-environments (e.g., different rooms in their home, at school or work, in vehicles, outdoors), making it challenging to prioritize actions to reduce exposure. In China, air purifiers are a common mitigation strategy. The impacts of air purifiers on indoor air quality and personal exposure can differ greatly in real-world settings depending on the participants’ behavior, the home environment, and the selected purifier. This work uses low-cost monitors to compare the impacts of air filtration on indoor air and personal exposure. Before deploying low-cost monitors, steps needed to be taken to ensure data quality: low-cost air monitors were evaluated against reference measurements in multiple field locations (i.e. Atlanta, Hyderabad, Beijing, and Shanghai), and various calibration methods were developed to reduce monitor error and bias. Results highlight the need to calibrate low-cost monitors under the same conditions in which they will be deployed, and illustrate methods to reduce error that will allow low-cost monitors to make powerful insights into addressing additional air quality issues in the future. After evaluation and calibration, low-cost air monitors were installed indoors (in study participants’ bedrooms) and outdoors. Additionally, monitors were worn by study participants to measure personal exposure. To evaluate the impacts of bedroom air filtration, participants in Beijing (N=7 adult participants) and Shanghai (N=43 child participants) had filtration devices set up in their bedrooms. During the study, all participants experienced both true and sham (i.e., placebo, with the filters removed) filtration. Personal exposure to O3 was significantly lower than ambient levels due to low indoor concentrations. However, few conclusions can be drawn about the impacts of filtration on O3 and the micro-environmental exposure to O3 since indoor concentrations were so often below the detection limit of our monitors (6 ppb). Measurements suggested that indoor PM2.5 was primarily of outdoor origin (≥75%). Purifiers significantly reduced bedroom PM2.5 concentrations by 70% and 78% during true filtration in Shanghai and Beijing, respectively. The reduction to personal exposure was less prominent, but still significant (Shanghai=24% and Beijing=36%). The largest time-weighted exposure to PM2.5 occurred in the bedroom during sham filtration since children spent the most time there. This suggests that the bedroom is the most important environment to tackle to reduce personal exposure. True filtration reduced the contribution of the bedroom micro-environment below that of the classroom and other rooms at home, highlighting that the classroom and other home environments should be the next-microenvironments to be address to reduce these children’s exposure. These results highlight the importance of reducing outdoor PM2.5 levels, but show that Chinese residents can reduce their PM2.5 exposure by installing an effective air purifier in the indoor environment where they spend the most time. Reductions in multiple micro-environments are likely required to further reduce exposure to PM2.5.