medium in each impinger was replaced by fresh solution every 30 mins and assayed to determine

the virus concentration by using suitable dilution to an adequate count (i.e., 30-300 PFU). The

procedures for preparing plaque assay medium are presented in Appendix B. Five 2-hr trials

were conducted, and thus total evaluation time was 10 hrs.

 Since 12 and HOI are disinfective forms, an increased VRE of the iodine-treated biocidal

filter at high temperature and increased relative humidity (RH) was hypothesized due possibly to

iodine's sublimation and to increased dissolution through the hydrolysis of I2 to HOI. Therefore,

various environmental conditions were considered: room temperature (232 C) and low relative

humidity (355%, RT/LRH); high temperature (302 C) and LRH (HT/LRH); RT and medium

RH (505%, RT/MRH). Because the maximum inactivation of MS2 aerosolized from 0.1M

NaCl was reported to occur at 75% (Trouwborst and de Jong 1973), RHs below this level were

considered. Temperature and RH were adjusted by wrapping the dilution dryer with a heating

jacket and adding dry or humid dilution air to the system.

Removal Efficiency

 Removal efficiency of viral aerosols by the test filters can be expressed both as PRE and

as VRE. The particle size distribution (PSD) of the aerosols entering and penetrating the test

filters was measured by using a Scanning Mobility Particle Sizer (SMPS; Model 3936, TSI Inc.,

Shoreview, MN, USA) and the PRE was determined by using Eq. (3-1).


 PRE (%)= 1-- xP 100
 I NE) (3-1)

where NE is the number of particles entering the filter and Np is the number of particles

penetrating the filter.