Comparing the Aerosol Particle Size Distributions and Mass Concentrations. The possibility that singing, speaking and breathing generate aerosol particles of different size cannot be inferred by comparing particle number concentrations alone. Instead, we must compare the aerosol size distributions from these activities. Previously, two overlapping modes in the size distribution of particles from speaking and coughing have been identified. These have been attributed to distinct processes in this expiration process. The mode of lowest size is generated in the lower respiratory tract with a second mode generated in the region of the larynx, expected to be the most important in voicing. Figure reports the variation in mean number concentrations with particle size averaged over the 25 participants and includes the fitted distribution from Johnson et al. reported from a cohort of 15. Our distribution for speaking and singing is in excellent agreement with the shape of the distribution reported by Johnson et al. for particles larger than 800 nm diameter. Although the absolute concentrations are a factor of ~6 larger in our measurements, it should be recognised that the absolute value carries little meaning, reflecting only the instantaneous value recorded by the APS from the sampling funnel, which will depend on the sampling specifications. Measured size distributions for speaking and singing were fitted to bimodal lognormal distributions. The fits all gave the similar mean diameters and variance for both modes, further supporting the conclusion that speaking and singing can be treated similarly (Extended Data Table ). However, both vocalisations generate larger particles than breathing: although the size distribution from breathing is well-represented by a bimodal lognormal distribution, the larger mode is shifted to a smaller diameter and has a narrower variance than for speaking and singing. .