Particle and Gas-phase Evaluation of Air Cleaners Under Indoor Wildfire Smoke Conditions

BRETT STINSON, Baorong Luo, Aurelie Laguerre, Elliott Gall, Portland State University

     Abstract Number: 234
     Working Group: Indoor Aerosols

Abstract
The number of acres burned each year due to wildfires has grown significantly since 1991. Indoor air cleaning interventions that rely upon high-efficiency particle filters have been proven to reduce exposure to fine particulate matter. However, wildfire smoke emissions include a myriad of hazardous particle and gas-phase constituents; there exists limited testing of air cleaners under the extreme conditions of an indoor space impacted by outdoor wildfire smoke. This study characterized 12 air cleaning devices, experimentally determining their size-resolved particulate matter, volatile organic compound (VOC), and black and brown carbon clean air delivery rates (CADRs), as well as power draw and sound levels. Portable devices that remove pollutants from air via standard HEPA and pre-filters, activated carbon banks, particle charging, and hydrogen peroxide generation were tested, along with three low-cost, do-it-yourself (DIY) configurations comprised of MERV 13 filters affixed to a box fan. The “pull-down” method was employed in triplicate within a large, stainless steel chamber, using pine needle combustion emissions as the challenge aerosol to simulate wildfire smoke. Results show that pine needle smoke PM2.5 CADRs were generally consistent with the smoke CADRs determined by standard test methods, for those air cleaners for which data was available. Two of the DIY configurations proved to be the most effective at removing larger particles (1–2.5 µm), with average CADRs of 1032 and 574 m³/h, respectively. In contrast with air cleaners that have HEPA filters, particulate matter CADRs for DIY air cleaners decreased with decreasing particle diameter. Among the air cleaners designed to remove gas-phase pollutants via activated carbon, meaningful VOC CADRs were realized, with two devices yielding benzene CADRs in excess of 200 m³/h. Air cleaners that added reactive species to the air yielded mixed results and warrant further analysis. These results show a variety of air cleaners can meaningfully remove indoor wildfire smoke under a realistic challenge, albeit in controlled conditions. Generally, gas-phase air cleaning yielded, at best, modest CADRs. This, along with substantial variability in PM CADRs across air cleaners indicates the need for further study and thoughtful public messaging regarding selection of air cleaners to comprehensively address indoor exposures to wildfire smoke of outdoor origin.