Evaluation of surface charge decay and initial filtration performance of electret respiratory mask filters exposed to IPA, DIW, and saliva

Electret respiratory masks are widely used to protect against airborne pathogens and fine particulate matter, but their electrostatic performance can deteriorate under realistic environmental exposures that are not fully represented by current IPA-based discharge tests. This study examines how such exposures influence initial filtration efficiency and surface charge density of three commercial masks (KF94, KF80, and a procedure mask). Size-resolved particle penetration was measured with a scanning mobility particle sizer (SMPS) for combined-mask specimens under five conditions: untreated, IPA immersion, saturated IPA vapor exposure, deionized water (DIW) immersion, and artificial saliva immersion. Layer-resolved measurements were performed under the same conditions except for IPA immersion. Layer-resolved penetration data were interpreted with a single fiber filtration efficiency (SFFE) model to estimate effective surface charge densities of the electret layers and to reconstruct mask-level penetration. IPA treatments produced the highest penetration for all mask types, consistent with a substantial reduction in electrostatic capture. DIW and artificial saliva produced mask-dependent changes in penetration, with generally greater increases after saliva exposure than after DIW exposure. These changes were largest for KF80, intermediate for the procedure mask, and smallest for KF94. SFFE-based inversions provided estimates of changes in effective surface charge density, although the reconstructed penetration did not always coincide with the directly measured combined-mask curves. Overall, the experimental and modeling results highlight the role of electret layer design and show that DIW and artificial saliva exposures provide information complementary to standard IPA discharge when evaluating the environmental durability of electret respirator filters.