Probing the Nanoparticle Loading Characteristics and the Filtration Performance with the Continuous and Intermittent Use of Disposable Filtering Masks

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/m3, 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.