The critical influence of particle charge neutralization on surgical mask and N95 respirator filtration efficiency

Abstract

This study investigates the critical influence of particle charge neutralization on the particle filtration efficiency (PFE) of surgical mask media and N95 respirator media across various inhalation face velocities. Surgical masks rely heavily on electrostatic attraction from charged electret fibers to achieve high filtration ratings. We compared the PFE of both mask types under three aerosol charge conditions—highly charged (Non-Neutralizer), X-ray neutralized, and Corona Discharge neutralized—at three face velocities (15.9 cm/s, 10.6 cm/s, and 5.3 cm/s) using 100 nm test particles. Results confirmed that the X-ray neutralizer achieved the closest state to the theoretical Boltzmann charge equilibrium for 100 nm particles (∼19 % charged fraction), establishing the lowest baseline for mechanical filtration efficiency. Filtration efficiency was highest in the Non-Neutralizer condition (up to ∼ 98 %). For surgical masks, the electrostatic contribution was maximized at the high face velocity of 15.9 cm/s, accounting for a drop of up to 20 % in PFE upon neutralization. In contrast, the N95 respirator media maintained an FE of≥95 % even when the challenge aerosol was completely neutralized by the X-ray Neutralizer, fulfilling the minimum requirements of the TIS 2480–2563 standard. The Corona Discharge neutralizer consistently yielded higher PFE values than the X-ray neutralizer for both mask types, suggesting it fails to completely establish a neutral equilibrium. This work quantitatively demonstrates that while surgical mask performance is critically dependent on electrostatic forces, N95 compliance is guaranteed by its inherently robust mechanical filtration.