Characterization and size distribution of initial droplet concentration discharged from human breathing and speaking

Abstract

A study of the aerodynamic characteristics of aerosol expiration is important for understanding the size distribution of droplet concentration in COVID-19 disease transmission. This study measured the initial concentration and size distribution of droplets released during four breathing processes: nose breathing, mouth breathing, reading alphabets and counting numbers. Influencing factors on droplet generation were studied by statistical analyses. Significant differences in droplet concentration among the four breathing activities in pairs were found (p < 0.001), except for reading alphabets and numbers (p = 1). The droplet concentration during nose breathing (p < 0.05), but not mouth breathing (p = 0.136), of male subjects, was found significantly higher than that of female subjects. The droplet concentration generated by speaking during letters reading with special phonemes, for example, /i:/, was significantly (p < 0.05) higher than reading letters without phonemes. The discharged droplet sizes from four breathing activities were dominated by small droplets (dp < 1.037 μm of over 50% and dp < 2.642 μm of over 80%). Basically, no particles larger than 8 μm were detected by the aerodynamic particle sizer. The inference indicates a possible aerosol transmission of disease during non-symptomatic aerosol-producing activities such as breathing or speaking and may elucidate the disease transmission pathway of COVID-19.