Assessment of personal and residential outdoor fine particulate matter exposure using low-cost sensors in a long-Covid patient population

Understanding the relationship between residential outdoor and personal PM_2.5 exposure is essential for accurately characterizing individual exposure, identifying key pollution sources, and developing targeted mitigation strategies. This study examines residential and personal PM_2.5 exposure levels and their interrelation in a long COVID population in the Netherlands. Residential outdoor PM_2.5 exposure was monitored using 73 low-cost continuous sensors deployed over an average of 131 days per participant. In parallel, 264 24-hour personal PM_2.5 measurements were collected using an Ultrasonic Personal Air Sampler (UPAS), with multiple measurements per participant spanning different seasons. Participants completed a detailed exposure questionnaires to document potential sources and behavioral patterns. Overall, personal PM_2.5 exposure levels (mean: 25.4 µg/m³) were higher than residential outdoor levels, with a mean difference of 18.4 µg/m³. When twelve influential personal measurements >50 µg/m³ were excluded, the mean difference decreased to 10.1 µg/m³. The 172 paired 24-hour measurements of personal and residential PM_2.5, revealed a moderate overall correlation (r = 0.27), with a stronger longitudinal within-person correlation (r = 0.39). Key contributors to the observed difference between personal and residential outdoor exposure included tobacco smoke exposure, the presence of a fireplace in the home, and increased ambient temperature. These findings suggest that patients in our study are exposed to PM_2.5 concentrations higher than the WHO air quality guidelines (5 ug/m³) potentially exacerbating already existing health problems. Furthermore, we identified environmental and behavioral factors affecting their exposure patterns providing opportunities to mitigate PM_2.5 exposures by long COVID patients.