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 (PM_2.5) 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 PM_2.5. 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, PM_2.5, 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 PM_2.5, 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 (<i>p</i> < 0.001). GM for PM_2.5 decreased by 45% from 17.12 to 9.16 µg/m³ (<i>p</i> < 0.001). We found that an increase in air purifier use resulted in a significant decrease in NO₂ and PM_2.5, and an increase in stove usage increased NO₂. HEPA/carbon filters have the potential to improve indoor air quality by reducing NO₂ and PM_2.5, enabling the tailoring of interventions to mitigate these air pollutants.