Aerosol emission rates from breathing, speaking, and speaking with a surgical mask.

Transmission risk assessment of airborne diseases such as COVID-19 requires a detailed understanding of respiratory aerosol generation and emission during activities such as breathing and speaking, as well as the influence of protective devices such as surgical face masks. We measured integral aerosol emission rates from n = 44 participants during breathing, speaking, and speaking while wearing a surgical mask, with each condition performed for 20 min. All measurements were conducted in a closed 20 m3 cabin under standardized initial conditions in an operating theater environment. Particle emission rates were log-normal distributed across participants. Median emission rates were 60 particles per second (P/s) for breathing (n = 35, IQR 24-152 P/s), 135 P/s for speaking (n = 41, IQR 56-327 P/s), and 278 P/s for speaking with a surgical mask (n = 29, IQR 157-492 P/s). Under the investigated conditions, wearing a surgical mask did not reduce total aerosol emission and was associated with a higher emission rate (median ratio 1.34, 95% CI [1.04-1.75], two clearly separated observations omitted). This observation may be explained by a combination of effects. First, the present measurements reflect total particle emission into the environment and therefore capture system-level behavior, including leakage, rather than material filtration efficiency. Second, previous studies have reported that mask use can alter respiratory mechanics, which may contribute to changes in aerosol emission. These findings may be relevant for assessing long-range transmission risk under comparable environmental conditions. At the same time, they do not contradict the established effectiveness of surgical masks in reducing droplet-mediated short-range transmission.