Assessing the effectiveness of using various face coverings to mitigate the transport of airborne particles produced by coughing indoors

Abstract

Exposure to respiratory droplets contributes greatly to the spread of SARS-CoV-2 virus during the COVID-19 pandemic. This study investigates the effectiveness of various face coverings to reduce cough-generated airborne particle concentrations at 0.3, 0.9, and 1.8 m away from the source in an indoor environment. We measured the particle number concentration (PNC) and particle size distribution under seven different conditions: (1) no face covering; (2) face shield only; (3) cloth mask; (4) face shield + cloth mask; (5) surgical mask; (6) face shield + surgical mask; (7) N95 respirator or equivalent (i.e., KN95 mask). We observed significant increases in PNCs at 0.3 m under conditions #1-4 and a trend toward an increase at 1.8 m, compared to the background. The face shield by itself provided little protection with a particle reduction of 4 ± 23% relative to no face covering, while the cloth masks reduced the particles by 77 ± 7%. Surgical and N95/KN95 masks performed well and substantially reduced the cough droplets to ≤6% at 0.3 m. In this study, most cough-generated particles were found less than 2.5 µm with an average mode diameter of ∼0.6 µm at 0.3 m. Approximately 80% of the particles ≤2.5 µm were able to travel to 0.9 m, and 10% of the particles ≤1.1 µm likely reached 1.8 m. Based on these results, face coverings, especially surgical and N95/KN95 masks, should be recommended as effective preventive measures to reduce outward transport of respiratory droplets during the COVID-19 pandemic. Copyright © 2020 American Association for Aerosol Research.