Downstream particle counting quantifies exposure reduction by miniaturized electrostatic precipitation compared to fibrous filtration.

Conventional respirator testing emphasizes filtration efficiency, but this metric does not fully capture how many particles ultimately reach the wearer. In this study, a standard N95 respirator and three prototype miniaturized electrostatic precipitator (mEP) masks, Mask A, Mask B, and Mask C, were evaluated using controlled aerosols of 1 µm, 4 µm, and mixed 1 + 4 µm polystyrene latex (PSL) particles. Rather than relying only on efficiency percentages, we quantified absolute downstream particle concentrations to compare passive fiber-based filtration with externally powered electrostatic particle removal strategies. All respirators reduced downstream particle concentrations dramatically compared with the no-mask control, typically by two to three orders of magnitude. For 1 µm PSL (~6.7 × 10⁵ particles min-1 without protection), Mask C allowed only ~8.8 × 10² particles min-1 , compared with ~1.67 × 10³ particles min-1 for the N95. The N95 served as the benchmark reference across aerosol conditions. SEM imaging confirmed dense PSL deposition under no-mask conditions and markedly reduced downstream deposition after respirator filtration, while EDS spectra verified PSL composition. These findings show that reporting absolute particle counts provides a direct, exposure-relevant framework for evaluating respirator performance.