Effect of Vocalization on Human Aerosol Dynamics: Whispering Produces More Aerosols than Speaking

Objectives: Sound pressure and exhaled flow have been identified as important factors associated with higher particle emissions. The aim of this study was to assess how different vocalizations affect the particle generation independently from other factors.

Design: Experimental study.

Methods: Thirty-three experienced singers repeated two different sentences in normal loudness and whispering. The first sentence consisted mainly of consonants like /k/ and /t/ as well as open vowels, while the second sentence also included the /s/ sound and contained primarily closed vowels. The particle emission was measured using condensation particle counter (CPC, 3775 TSI Inc.) and aerodynamic particle sizer (APS, 3321 TSI Inc.). The CPC measured particle number concentration for particles larger than 4 nm and mainly reflects the number of particles smaller than 0.5 µm since these particles dominate total number concentration. The APS measured particle size distribution and number concentration in the size range of 0.5-10 µm and data were divided into >1 µm and <1 µm particle size ranges. Generalized linear mixed-effects models were constructed to assess the factors affecting particle generation.

Results: Whispering produced more particles than speaking and sentence 1 produced more particles than sentence 2 while speaking. Sound pressure level had effect on particle production independently from vocalization. The effect of exhaled airflow was not statistically significant.

Conclusions: Based on our results the type of vocalization has a significant effect on particle production independently from other factors such as sound pressure level.