Aerosol Emission During Speech: Investigating the Role of Glottal Configuration and Respiratory Effort
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Introduction
Speech-driven aerosol generation plays a key role in airborne disease transmission, yet the physiological mechanisms remain poorly understood. While prior research suggests vocal fold vibration contributes to aerosol production, airflow turbulence and glottal configuration may be stronger determinants. This study examines how the type of phonation influences aerosol generation while controlling for respiratory effort.
Methods
Five healthy female adults (22–43 years) sustained vowels across six phonation types: modal voicing, glottal fry, falsetto, whispered speech, loud speech, and vowels preceded by /h/. Aerosol concentration and size distribution (0.1–20 µm) were measured using an aerodynamic particle sizer (APS). Laryngoscopy quantified normalized glottal gap, and CO 2 range was recorded to control for respiratory effort. Bayesian regression models assessed relationships between phonation type, aerosol generation, and physiological predictors.
Results
Whispering and loud speech produced the highest aerosol concentrations, while glottal fry generated the least. Smaller aerosol particles (0.1–1 µm) were most prevalent across tasks, highlighting their potential for airborne transmission. Whispering exhibited a bimodal aerosol distribution, with increased emissions at both the smallest (0.1–1 µm) and largest (10–20 µm) particles sizes. Despite the assumption that vocal fold vibration is necessary for aerosol production, whispering, a voiceless phonation, generated the most aerosols, suggesting airflow turbulence and glottal configuration are stronger contributors. Normalized glottal gap was the strongest predictor of aerosol output, followed by CO 2 range, while harmonics-to-noise ratio had a smaller effect.
Conclusion
Vocal fold vibration alone is not necessary for high aerosol generation; turbulent airflow through a partially open glottis is a key driver. These findings have implications for airborne disease transmission, particularly in densely occupied environments. Future research should explore real-world speech patterns to refine strategies for minimizing respiratory particle exposure.
