Bench‐Scale Evaluation of In‐Duct Air Filter Performance Against Simulated Wildfire Smoke: Assessing Long‐Term Efficiency

Wildfire smoke poses significant health risks. Although air filtration is a recommended mitigation strategy, the long‐term performance of home furnace filters when exposed to wildfire smoke has not been extensively investigated. This study addresses this research gap by evaluating the performance of commercially available in‐duct MERV (Minimum Efficiency Reporting Value) 7 and MERV 13 filters against simulated wildfire smoke using a bench‐scale testing method. Each filter was subjected to 100 measured exposures, with particulate matter (PM) measured upstream and downstream. Exposed filters were examined using Scanning Electron Microscopy (SEM) to gain insight into the morphological nature of particles captured by filters. MERV 13 filter particle removal efficiency, based on mass, dropped from 80% initially to 30% in the final test. The efficiency, based on particle count, dropped from an initial value of 35%–20%. For particles with a diameter between 3–10 μ m, MERV 13 filter performance, based on particle count, dropped from ~90% in the first test to ~40%. For particles with a diameter of 1–3 μ m, the filter performance dropped from ~60% to ~0%. The removal efficiency of particles with a diameter of 0.3–1 μ m was ~25% with a slight increase in efficiency over time. MERV 7 filter particle removal efficiency, based on mass, was ~18% at the beginning, then linearly dropped to ~8% by the last test. Based on particle count, the filter efficiency was approximately 18%–22%. SEM analysis indicated that the particles captured by the filters were mostly droplet‐like structures commonly known as “tar balls” generated from biomass pyrolysis. These droplets range in size from submicrons to ~5 μ m, consistent with measurements from the optical particle counters.