calculated by following the same equation used for sterile DI water (shown in Figure 4-5).

Similar to the MS2 aerosols generated with sterile DI water (shown in Figure 4-3), NPFU

increased as particle size increased. However, the values at three RHs increased less with

increasing particle size than NTheopFU(n = 3), and were also lower than those for sterile DI water

(Table 4-3). It is plausible that the abundance of tryptophan in tryptone induces hydrophobic

interaction with MS2 protein and also provides surface for MS2 to reside on or attach to. This

phenomenon can cause NPFU increase in proportion to surface rather than to volume.

 It should also be noted that NPFU was significantly lower than that generated from sterile

DI water at LRH. The reason for this phenomenon is the contribution of tryptone to the solid

content of droplet nuclei, which leaves less room for MS2. This contribution can be verified by

analyzing NRNA in the samples. By using the calculation used for MS2 aerosols generated from

sterile DI water, NRNA of select particle sizes at three RHs was calculated (shown in Table 4-7).

Clearly, NRNA was significantly smaller than that of MS2 aerosols generated from DI water

(Table 4-4), due to the significant solid fraction resulting from the presence of tryptone. The

NR4A of a given particle size was higher at LRH than at MRH and HRH due to increased solid

contents; meanwhile, insignificant difference was observed between MRH and HRH.

 Table 4-8 presents NPFU/,' i at three RHs. At LRH, NPFU/,; i shows similar values

among different particle sizes. The result demonstrates that when viruses are not exposed to the

adverse effect of increased RH, the presence of tryptone exerts no protective effect. NPFU/,'

at HRH was significantly higher than that at LRH and MRH, as well as at HRH for MS2 aerosols

generated from sterile DI water. This observation can be explained by the encasement effect of

tryptone for MS2 aerosols in the hostile condition of HRH. A similar study demonstrated high

recovery of MS2 aerosols at all RHs ranging from 20 to 80% due to the protective effect of