It’s enough just to say that tiny aerosol particles flying out of the mouth infect the interlocutors, according to experts in aerosol physics from the University of California at Davis, whose work appeared on the PLOS ONE website.
During speech, each of us produces a fairly large number of aerosols – respiratory particles about one micron in size. Aerosols are too small to be seen with the naked eye, but large enough to travel through the air, carrying agents such as the influenza virus or SARS-Cov-2.
As a rule, the louder a person speaks, the more particles he emits. Some people, for a reason that is still unclear, are aerosol “superpropagators”: they emit 10 times more particles than others. The speed of the air flow and the ability to spread aerosols also depends on the phonetic features of the language: as studies show, the more vowels there are in the speech, the higher the emission, the more fricatives (c, s, f, c), the lower the emission. (There is a temptation to relate this data to the melodiousness of the Italian language.)
Calculating how easily a virus like SARS-CoV-2 can spread by aerosol is quite complicated. It depends on many factors: how many viruses are in the pulmonary fluid, how easily they form into drops, what is the contagiousness of the virus, what is the movement of air in the room, etc. All these are questions for virologists and epidemiologists. We can perceive the results of this study as another reminder of the importance of maintaining distance.