Impacts of Portable\nAir Purifiers on the Oxidative\nPotential and Sources of Organic Matter in Indoor PM<sub>2.5</sub>

Organic matter (OM) is a major contributor to the oxidative\npotential\n(OP) of indoor PM<sub>2.5</sub>. Portable air purifiers equipped with\nhigh-efficiency particulate air (HEPA) filters are known to effectively\nremove indoor PM<sub>2.5</sub> mass concentrations. However, their\nimpacts on the OP and sources of indoor PM<sub>2.5</sub> OM and whether\nthese impacts could further affect the OP of indoor PM<sub>2.5</sub> metals remain poorly understood. In a crossover trial, each of the\n43 asthmatic children underwent a 2-week true filtration (HEPA + activated\ncarbon [AC]) and sham filtration (no HEPA + no AC), with randomized\norder. PM<sub>2.5</sub> samples, simultaneously collected in participants’\nbedrooms and outside their homes, were measured for mass concentration,\ncomposition, mass-normalized OP (OP<sub>m</sub>, OP per mass), and\nvolume-normalized OP (OP<sub>v</sub>, OP<sub>m</sub> × mass concentration).\nCompared to the sham filtration, indoor PM<sub>2.5</sub> OM mass was\n34% lower, OP<sub>m</sub> was 70% lower, and OP<sub>v</sub> was 80%\nlower during true filtration. The reduction in OM OP<sub>v</sub> was\nlargely attributed to removing more reactive outdoor OM and indoor\nsecondary OM. The change in OM composition also contributed to the\nreduced PM<sub>2.5</sub> metals’ OP<sub>m</sub>. Our results\nsuggest that indoor air purifiers with HEPA and AC filters efficiently\nreduce PM<sub>2.5</sub> OP<sub>v</sub> by removing OM.