Nitrogen dioxide (NO₂) and particulate matter of 2.5 microns (PM_2.5) are air pollutants that impact health, especially among vulnerable populations with respiratory disease. This study identifies factors influencing indoor NO₂ and PM_2.5 in low-income households of older adults with asthma who use gas stoves in Lowell, Massachusetts. Environmental sampling was conducted in 73 homes, measuring NO₂, PM_2.5, fractional stove-use, temperature, and humidity for 5–7 days. Participants were recruited between December 2020 and July 2022. Questionnaires were used to collect data on factors influencing indoor NO₂ and PM_2.5 concentrations. Daily outdoor NO₂ and PM_2.5 concentrations were obtained from a United States Environmental Protection Agency (EPA) monitoring station. Paired t-tests were conducted between indoor and outdoor NO₂ and PM_2.5 concentrations, and linear regression was used to evaluate factors influencing indoor NO₂ and PM_2.5 concentrations. The average indoor concentration for NO₂ and PM_2.5 were 21.8 (GSD = 2.1) ppb and 16.2 (GSD = 2.7) µg/m³, respectively. Indoor NO₂ and PM_2.5 concentrations exceeded outdoor concentrations significantly. In multiple regression models, season and pilot light stove use significantly predicted indoor NO₂. Season and air freshener use for 6–7 days/week significantly predicted indoor PM_2.5. Season-influenced higher indoor concentrations are likely due to reduced ventilation in colder months in the Northeast U.S.

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 (p < 0.001). GM for PM_2.5 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 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.