Particle emission rate/concentration while reading a passage of text aloud (the “Rainbow” passage), at three different loudness levels. (A) Superimposed representative recordings of amplitude (arb. units) for an individual (F4) reading the passage at three different voice amplitudes, and (B) the corresponding number/concentration of particles measured by the APS versus time. Color code same as in (A). (C) Particle emission rate/concentration as a function of root mean square amplitude, Arms, for 10 participants. There are 3 points for each person, representing 3 voice amplitudes, color code same as Fig. 2C. Solid line is a power law fit with exponent 0.96, correlation coefficient ρ = 0.865 and Pearson’s p value = 6.8 × 10−10. (D) Representative particle size distribution for the one individual (F4).