In Case You Missed It

By Lindsay Yee, UC Berkeley

Have you ever wondered what your indoor air quality is like during wildfire events that may lead to intrusion of air pollution inside your living spaces? With the increasing prevalence of wildfire smoke impacting urban areas, there is great interest in how to protect human health in indoor environments with various methods spanning more economical do-it-yourself (DIY) designs and commercially available engineering controls (e.g. commercial air cleaners). Stinson et al. (2024) conducted a comprehensive study testing 13 different air cleaners and three DIY configurations under simulated conditions of wildfire smoke penetrating an indoor environment. Combusted pine needle emissions were introduced to an experimental 17.8 m³ insulated simulation chamber equipped with ventilation controls and a suite of atmospheric instrumentation. Tested air cleaners had various operating mechanisms (e.g. high-efficiency-particulate-air (HEPA) filter, sorbents for gas-phase pollutant removal, as well as additives—ions, H₂O₂, and/or water vapor). Three DIY configurations based on the popularized Corsi-Rosenthal Box (CR Box), consisting of four or five furnace filters (e.g. MERV 13) taped together to form a cube around a box fan’s inlet, were also studied.

Center for Aerosol Science and Engineering

Each air cleaner’s ability to remove particulate matter (as a function of size), black and brown carbon, and VOCs focusing on benzene, toluene, and C8 aromatics was tested. The findings revealed that DIY configurations demonstrated high clean air delivery rates (CADRs) for larger particles but were less effective for smaller ones in comparison to the HEPA filtration units that had more consistent CADRs across all studied sizes. Air cleaners employing only additive technologies were variable or ineffectual at removing PM. Brown and black carbon CADRs were similar to the PM CADRs. VOC CADRs were variable, highest for the largest sorbent containing air cleaners, and those with additives had mostly low CADRs.

Pollutant modelling was employed using the determined CADRs for four representative air cleaners to simulate a 48-hour event (24 hours of wildfire smoke impact with air cleaner on, followed by 24 hours after ambient levels return to background with air cleaner off). The modelling assessed the efficacy of air cleaners in reducing pollutant levels and subsequent exposure, considering factors like the sorption of benzene on indoor surfaces. Overall, the modelling results demonstrate that use of devices having even modest PM CADRs and benzene CADRs can significantly reduce pollutant levels and resulting exposure. This study is highly informative for those thinking about practical ways to minimize the impacts of indoor exposure to wildfire smoke.

Read more in the literature:

W. Stinson, B., Laguerre, A. and T. Gall, E.: Particle and Gas-Phase Evaluation of Air Cleaners Under Indoor Wildfire Smoke Conditions, ACS ES&T Air, doi:10.1021/acsestair.3c00083, 2024.