Charge-Driven Degradation of Residential Electret HVAC Filters under Wildfire Smoke Exposure

Wildfire smoke poses an increasingly significant threat to indoor air quality; however, the performance and durability of residential HVAC filters under sustained exposure to wildfire smoke remain poorly understood. Here, we show that wildfire smoke degrades electret filter performance through mechanisms fundamentally distinct from those captured by standard filtration tests. Combining laboratory-generated flaming and smoldering wood smoke, field sampling during prescribed burns, and controlled soot particle challenges, we demonstrate that filtration efficiency can collapse rapidly at particle loadings far below those associated with appreciable pressure drop increases. This behavior is driven primarily by soot-rich particles, which induce rapid and irreversible neutralization of electret charge rather than by progressive mechanical clogging or organic aerosol deposition alone. As a result, pressure-based filter-replacement criteria substantially overestimate usable filter lifetime during wildfire smoke events. Incorporating these experimentally constrained degradation pathways into a dynamic indoor air model reveals that effective filter lifetime during wildfire episodes can be reduced from months to days, even under moderate outdoor concentrations. Application to a regional wildfire event using U.S. EPA monitoring data further demonstrates that indoor protection varies significantly with building characteristics and ventilation strategies. These results identify soot-driven electret charge neutralization as a critical vulnerability of typical residential HVAC filters, reframing filtration performance under wildfire smoke exposure as primarily constrained by electret charge stability rather than pressure-drop-driven loading.