aggregates or attached to the surface of the solid content. At the same time there are particles

that contain no MS2.

 The stability of MS2 aerosols was investigated by comparing NPFU/ i (i.e., infectious

MS2/total MS2) of select particle sizes at three RHs as shown in Table 4-6. NPFU in a unit RNA

was significantly higher at LRH than at MRH and HRH (one-way ANOVA, p-value < 0.05),

indicating stability and preservation of MS2 infectivity in aerosols at LRH. No significant

difference was observed between the value at MRH and HRH (unpaired Student's t-test, p-value

> 0.05), indicating similar survival capacity. This observation can be attributed to the increase in

air- to-water interface at increased RHs, which results in the exposure of aerosols to unbalanced

force leading to a decrease of NPFU (Adams 1948). NPFU/ i; generally increased as particle size

increased at MRH and HRH in spite of the adverse effect at increased RHs. This result

demonstrates the shielding effect of bigger particles. Indeed, MS2 aerosols, which are less stable

at 50% and 85% than at 25% RH, can be protected by forming aggregates to reduce exposure to

the adverse influence of increased RH. Meanwhile, at LRH, NPFU in a unit RNA differed

insignificantly among the various particle sizes investigated. This shows that, without the

adverse effect of RH, shielding due to aggregation decreases in importance to survival.

MS2 aerosols generated from tryptone solution

 Experiments were also conducted with tyrptone solution as the aerosolization medium.

As shown in Figure 4-4 for LRH, the presence of tryptone in the nebulizer suspension shifted the

PSD towards the bigger particle size range compared to the MS2 aerosols generated from sterile

DI water as Eq. (4-2) predicts. The PSD of infectious viruses was between number- and mass-

based PSD, i.e. its n value was between 2 and 3 as shown in Table 4-3. At other RHs, a similar

phenomenon was also observed (Appendix D). The NPFU of a given particle size was also