Impacts of Portable Air Purifiers on the Oxidative Potential and Sources of Organic Matter in Indoor PM_2.5

Organic matter (OM) is a major contributor to the oxidative potential (OP) of indoor PM2.5. Portable air purifiers equipped with high-efficiency particulate air (HEPA) filters are known to effectively remove indoor PM2.5 mass concentrations. However, their impacts on the OP and sources of indoor PM2.5 OM and whether these impacts could further affect the OP of indoor PM2.5 metals remain poorly understood. In a crossover trial, each of the 43 asthmatic children underwent a 2-week true filtration (HEPA + activated carbon [AC]) and sham filtration (no HEPA + no AC), with randomized order. PM2.5 samples, simultaneously collected in participants’ bedrooms and outside their homes, were measured for mass concentration, composition, mass-normalized OP (OPm, OP per mass), and volume-normalized OP (OPv, OPm × mass concentration). Compared to the sham filtration, indoor PM2.5 OM mass was 34% lower, OPm was 70% lower, and OPv was 80% lower during true filtration. The reduction in OM OPv was largely attributed to removing more reactive outdoor OM and indoor secondary OM. The change in OM composition also contributed to the reduced PM2.5 metals’ OPm. Our results suggest that indoor air purifiers with HEPA and AC filters efficiently reduce PM2.5 OPv by removing OM.