tryptone (Dubovi and Akers 1970). Within the same context, increased NPFU /' for MS2

aerosols generated from tryptone solution than that for MS2 aerosols generated from suspensions

in DI water was expected at MRH. However, as seen in Tables 4-6 and 4-8, insignificant

increase was observed. This observation, along with the significant decrease ofNpFU compared

to that for sterile DI water at LRH, suggests an adverse effect of tryptone at LRH and MRH,

rather than a protective effect. This result can be attributed to the supersaturated condition of

tryptone in droplet at LRH and MRH. Although this observation does not agree with the Dubovi

and Akers (1970) study in the aspect that they observed high recovery of MS2 at LRH and MRH,

Trouwborst and de Jong (1973) demonstrated that phenylalanine does not exert a protective

effect for MS2 aerosols under supersaturated conditions. They mentioned that crystals or the

process of crystallization can be deleterious to MS2 aerosols. As the RH keeps decreasing,

droplets may reach the crystallization RH (CRH), which is the maximum RH at which solutes

maintain the aqueous phase without experiencing crystallization at a supersaturated condition.

The CRH is always below the deliquescence RH (DRH). It was reported that the DRH and CRH

of ammonium sulfate are 80% and 40%, respectively (Seinfeld and Pandis 1998). Also, some

common components of ambient aerosols have a DRH between 70% and 85%. Although the

CRH of these components was not reported, it is reasonable to expect that the value is similar to

that of ammonium sulfate unless the species are not hygroscopic. Within the same context, the

CRH of various components of the spray medium can be around 40%, which is about the MRH

investigated in this study.

MS2 aerosols generated with artificial saliva

 Figure 4-6 shows the PSD of number-based, mass-based, and infectious counts as a

function of particle size at LRH. Apparently, the PSD was shifted to an even bigger particle size