With the pandemic crisis and long-lasting air pollution, reuse of disposable filtering masks has been prevalent while not being recommended. Different aerosol exposure conditions such as an extended continuous use and an intermittent repeated use lead to different particle loading behavior, affecting the effective service life of filters in terms of resistance and efficiency. Thus, the service life analysis considering the realistic wear situation is needed for guiding the proper filtering mask usage. This work investigated the effect of particle exposure and storage conditions on the performance and resistance of a single use, disposable foldable type filtering masks. An intermittent exposure condition was set to simulate a harsh exposure scenario of particle concentration of 300 μg/m 3 , 8−10 h use, and intense physical load with 85 L/min inhalation rate. For an extended use situation with solid particles, resistance was a limiting factor of the effective useful time of filtering mask. Compared with the continuous exposure, the intermittent exposure with humid storage condition accelerated the performance deterioration, limiting the service life. The causes for the divergent performance behavior were probed in the nanoscale, employing the Xμ-CT analytical technique; this allowed visualization of distinctive loading characteristics of aerosol, such as surface clogging, depth filtration, and aerosol aggregation. The significance of this study lies in the analytical approach that enabled the 3D probing of nanoparticle-loaded filters and in the experimental design that mimicked the practical use conditions.

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Worldwide attention has been paid to effective protection strategies against the COVID-19 pandemic. Filtering masks are generally kept for a certain period of shelf-life before being used, and frequently, they are used repeatedly with recurrent storages. This study investigates the effect of storage temperature and humidity on the structural characteristics and charges of an electret filter, associating with the filtration performance in terms of efficiency and pressure drop based on a practical use-storage scenario. For the repeated use conditions with recurrent storage, humid storage conditions significantly deteriorated the filtration efficiency as hygroscopic particles quickly wetted the surface and masked the surface charges. The high temperature rapidly deteriorated the filter charges and caused a lowered electrostatic filtration efficiency. In a heated condition, the web became fluffier, yet it did not directly affect the pressure drop or mechanical filtration efficiency. The approach of this study is progressive in that rigorous analysis was performed on examining the particle morphology and internal structure of filter media with varied storage conditions to link with the filtration performance and the effective lifetime. This study intends to provide a scientific reference guiding a desirable storage condition and replacement cycle of filtering masks considering the actual use habits and storage environment.