Effectiveness of HEPA/Carbon Filter Air Purifier in Reducing Indoor NO2 and PM2.5 in Homes with Gas Stove Use in Lowell, Massachusetts.

Nitrogen dioxide (NO2) and particulate matter of 2.5 microns (PM2.5) impact health outcomes. This study utilized a pre- to post-test study design to evaluate the impact of air purifiers fitted with a high-efficiency particulate air (HEPA) and carbon filters in reducing indoor NO2 and PM2.5. Sixty-seven low-income homes in Lowell, Massachusetts, were included in this study. Home visits were conducted every four months for 12 months. At each visit, we conducted environmental sampling, measuring indoor NO2, PM2.5, stove use, temperature, and humidity over 5-7 days. We collected environmental exposure data using questionnaires. Air purifiers were introduced after the 4th month. Linear mixed models were used to predict changes in NO2 and PM2.5, with independent predictors as fixed effects and homes as random effects. The geometric mean (GM) for NO2 decreased by 36% from 20.16 to 12.79 ppb (p < 0.001). GM for PM2.5 decreased by 45% from 17.12 to 9.16 µg/m3 (p < 0.001). We found that an increase in air purifier use resulted in a significant decrease in NO2 and PM2.5, and an increase in stove usage increased NO2. HEPA/carbon filters have the potential to improve indoor air quality by reducing NO2 and PM2.5, enabling the tailoring of interventions to mitigate these air pollutants.