UC Davis

Public health authorities have mandated wearing face coverings indoors as a tool for preventingthe spread of COVID-19. Since then, people have worn various face coverings, including masks and respirators, when such mandates have been in effect. While masks and respirators reduce respiratory particle emissions, various studies indicate that the efficiency of face coverings can vary substantially. Here, we characterized the outward particle emissions from a real person's speaking activity while wearing various cloth masks, surgical masks, respirators, bandanas, and neck gaiters in different wearing styles. In addition, we evaluated adding extra filters to cloth masks, crossed ear loops for surgical masks, and double masking (cloth over surgical). Cloth masks, surgical masks, respirators, and double masking reduce the outward particle emission rates on average by 43.8%, 79.7%, 88.4%, and 86.4%, respectively, for speaking. For all three types of surgical masks, crossing the ear loop did not yield a significant particle reduction compared to the standard wearing style. In contrast, the particle emission rates from two types of cloth face coverings—a bandana and two different neck gaiters—were greater than that for wearing no masks, suggesting that some face coverings shed non-respiratory particles. We also characterized the particle emission rate and size distribution from rubbing the masks against themselves and against human skin to quantify the non-respiratory particle emission from friction during speaking. Our results show that cotton made face coverings tend to emit more non-respiratory particles than noncotton made face coverings during speaking. The skin particles emission rates were similar to the non-cotton made face coverings, with particle size typically smaller than 0.58 μm. Furthermore, we characterized the non-respiratory particle emission by flowing particle-free air through the masks. The non-respiratory emission from the hand rubbing experiments and clean-air flow experiments had a positive linear correlation, suggesting cloth masks tend to emit more nonrespiratory particles by themselves due to the friction and air flow than respirators and surgical masks. The non-respiratory particle emission level is strongly correlated with the mask material. Additionally, the hand rubbing experiments had higher particle emission in the range of 2-15 μm compared to the speaking activity, which primarily produced particles in the range of 0.5-2 μm, indicating the non-respiratory particles were smaller on average than respiratory particles. Overall, our results provide further evidence that wearing masks can reduce the outward particle emissions, but with the efficacy dependent on the mask type.