A New Metric for Face Mask Evaluation

Since the outbreak of the COVID-19 pandemic nearly five years ago, most research evaluating the efficacy of face masks has focused on closed settings, where tiny particles at submicron levels, or aerosols, are forced into direct contact with masks. This “particle filtration efficiency” (PFE) approach, however, does not account for the reality of human daily experience, in which aerosols in open environments flow with air around masks without necessarily contacting their surfaces.

Lee at al. introduced a new analytic methodology, aerosol circumvention efficiency (ACE), to consider the likelihood of aerosol deposition on the surfaces of masks in open environments.

“The ACE method evaluates the amount of aerosol that circumvents a mask without depositing on its surface,” said author Seong Jin Kim. “It provides a safer metric than the PFE approach because it focuses on the initial deposition interaction between aerosols and mask surfaces before any filtration occurs.”

Using the new method, the researchers found that surgical masks achieve a 92.5% rate of efficiency in open environments, significantly greater than the rate of between 47% and 85.5% previously estimated using the PFE test. Although their performance is lesser than the 98.3% efficiency of N95 masks, the ACE results show that surgical masks perform better than previously thought.

Also, the new perspective reveals that the curvature of a mask, in addition to its filtration performance, is consequential to its overall effectiveness in everyday human environments.

“Building on this research, we anticipate our findings will provide a crucial foundation for designing new masks with optimized curvature to enhance aerosol circumvention and achieve better balance between effective filtration and breathability,” said Kim.

Source: “Aerosol deposition on face masks in an open environment during inhalation,” by Y. J. Lee, M. W. Moon, S. Chung, and S. J. Kim, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0231731 .

This paper is part of the Flow and the Virus Collection, learn more here .