Excellent piece from Nature in 2019 with both new results and a great summary of previous work.

Worth reading for the details. https://www.nature.com/articles/s41598-019-38808-z

“The particle emission rate during speech is linearly correlated with the amplitude (loudness) of vocalization, for four different languages tested.”

“Morawska and coworkers also reported that more particles are released when speech is voiced, which involves vocal folds vibration, rather than whispered, which does not.”

“The particle size distribution is independent of vocalization loudness or language spoken.”

That is interesting: you spray more but you spray the same stuff.

“Some individuals emit particles at a rate more than an order of magnitude larger than their peers, i.e., they behave as “speech superemitters.””

It’s not obvious (as they say in the paper) why some people do this and others don’t.

In their literature summary the include:

“Singing can increase the emission of droplets by 6 times over speech.”

“speech can release dramatically larger numbers of particles compared to coughing”

“Loudon and Roberts investigated the role of singing in the spread of tuberculosis and showed that the percentage of airborne droplet nuclei generated by singing is 6 times more than that emitted during normal talking and approximately equivalent to that released by coughing”

“Chao et al. used an interferometric imaging technique to obtain the size distribution of particles larger than 2 μm and found that counting aloud from 1 to 100 releases at least 6 times as many particles as an individual cough.”

That’s about 1 to 2 mins of speech by my estimate

“Morawska and coworkers reported that counting aloud for 10 seconds followed by 10 seconds of breathing, repeated over two minutes, releases half as many particles as 30 seconds of continual coughing, which in turn releases half as many particles as saying “aah” for 30 seconds.”

“the results strongly suggest that individual human speech patterns and speech-associated particle emissions are highly heterogeneous and thus might play a role in the transmission of some respiratory pathogens.”

“rate of particle emission during normal human speech is positively correlated with the loudness (amplitude) of vocalization, ranging from approximately 1 to 50 particles per second (0.06 to 3 particles per cm^3) for low to high amplitudes”