tryptone and saliva, it can be informed that both concentration and nature of solid materials

dissolved in the spray medium determine the size and fate of viral aerosols at any given RH.

 As discussed previously, three concerns relating to specific characteristics of viruses are

small particle size, shielding effect, and encasement effect of substances. We observed both a

shielding effect of aggregates and an encasement effect by the presence of inert materials for

200-nm viral aerosols. It should be emphasized that aerosols of this size are small enough to

reach the alveolar region of the lungs, and inhalation of one such single particle can easily attain

the minimum infectious dose of virus with enhanced shielding and the encasement effect. For

example, the NPFU resulting from the penetration of a single 200-nm particle through a filter or

respirator is equivalent to the NPFU resulting from the penetration of 100 30-nm particles of MS2

generated from DI water at HRH.

 Although the current study characterized one specific species (MS2 bacteriophage),

general characteristics applicable to other viral aerosols can be deduced from our findings. The

shielding effect of small aggregates is a common characteristic of general viruses because of

their tiny primary particle size and aggregated airborne state. In addition, as observed in the

encasement effect of tryptone, inert materials (e.g., dust in air or substances generated with

viruses) can exert a protective influence on viral aerosols in adverse conditions. These two

general properties can contribute to the survival of viruses in otherwise hostile circumstances

(e.g., sensitive RH and temperature) or even inactivation treatments, and to subsequent initiation

of infectivity and transmission of disease.