  The study of aerosols and droplets emitted from the oral cavity has become
increasingly important throughout the COVID-19 pandemic. Studies show
particulates emitted while speaking were generally much smaller compared to
coughing or sneezing. However, recent investigations revealed that they are
large enough to carry respiratory contagions. Although studies have shown that
particulate emissions do indeed occur during speech, to date, there is little
information about the relative contribution of different speech sounds in
producing particle emissions. This study compares airborne aerosol generation
in participants producing isolated speech sounds: fricative consonants, plosive
consonants, and vowel sounds. While participants produced isolated speech
tasks, a planar beam of laser light, a high-speed camera, and image software
calculated the number of particulates detected overtime. This study compares
airborne aerosols emitted by human participants at a distance of 2.54 cm
between the laser sheet and the mouth and reveals statistically significant
increases in particulate counts over ambient dust distribution for all speech
sounds. Vowel sounds were statistically greater than consonants, suggesting
that mouth opening, as opposed to place of vocal tract constriction or manner
of sound production, might be the primary influence in the degree to which
particulates become aerosolized during speech. Results of this research will
inform boundary conditions for computation models of aerosolized particulates
during speech.
