Viral aerosol survivability, transmission, and sampling were studied size-selectively in an environmental chamber, which simulated a typical indoor environment featuring a complex flow field and low viral aerosol concentration. MS2, HAdV-1, AIV, SIV, TGEV, and aMPV were tested as surrogates for common human viruses. Live virus titer, total virus concentration, and fluorescence intensity were measured to calculate virus relative recovery and survival. Because of the low viral aerosol concentration in the chamber, long-term sampling had to be conducted for virus quantification. Long-term sampling performance of the eight-stage non-viable Andersen cascade impactor was tested first. All six viruses were sampled for one and six hours at 25 deg C and 50% RH. The six-hour samples did not show much higher live virus titers than the one-hour samples, suggesting significant inactivation in the impactor. The six-hour tests did collect much higher total virus concentrations that resulted from PCR analysis. Impactor plate overloading which caused a decrease in sampling efficiency was observed in the six-hour tests. Due to higher survivability and lower uncertainty, MS2, HAdV-1, and AIV were further tested at different temperatures and humidities. All three viruses had lower inactivation rates at 25 deg C than at 30 deg C, but the effect was not significant for HAdV-1. Absolute humidity (AH) was found to be a better predictor of survival than relative humidity (RH). Using AH also removed the significant interaction between temperature and humidity, which exists when RH is used. MS2 and HAdV-1 had the lowest inactivation rates at low AH, and AIV had the lowest inactivation rate at high AH for the AH range from 8.8 to 15.2 g/m3, which is common in most indoor environments. Future tests are recommended at more extreme humidity levels.In the UVGI tests, the survival of MS2, HAdV-1 and AIV was significantly reduced when UV was used, showing the good potential of UVGI for indoor air disinfection. The inactivation damaged the nucleic acid, which reduced live virus titer and total virus concentration by similar rates. Based on relative recovery, virus inactivation rates due to UVGI were calculated for the three viruses. To quantify the virus susceptibility, a transient numerical simulation was conducted with Lagrangian particle tracking and log-linear inactivation kinetics. The average susceptibility of MS2 was 0.057 cm2/mJ with the range for one standard error to be [0.022, 0.098] cm2/mJ. For HAdV-1, the susceptibility was 0.056 [0.035, 0.079] cm2/mJ, and for AIV, it was 0.132 [0.031, 0.278] cm2/mJ. The result suggests that virus susceptibility to UVGI may be similar for air and water environments. Tests for different irradiance and dose levels are recommended to further investigate the inactivation kinetics and verify the numerical model. In the HVAC filter tests, the overall filtration efficiencies for fluorescein and for total virus were similar, but the filtration efficiency for total virus was significantly higher than that for fluorescein at about 1 µm particle diameter. This result suggests that using fluorescein may not accurately predict the filtration behavior of viruses for the small particles. For the chemical-free filters tested, no significant inactivation of MS2 was found in the filtration process. More than 95% of the aerosol mass collected was smaller than 4.7 µm, with the mass median diameter of about 1.5 µm. The particle size distribution was affected by suspension medium but not virus. If the nucleic acid was not damaged during a test, the physical loss of virus was better predicted by total virus (PCR) rather than fluorescein, and their difference could be larger for larger viruses. In the nebulizer fluid, no significant virus inactivation was found after the one-hour tests with 20 psi (138 kPa) compressed air, or after the six-hour tests with 10 psi (69 kPa) compressed air. The evaporation effect was more obvious for longer test duration or greater compressed air pressure. The nebulization rate of fluorescein was higher than that of virus.
University of Minnesota Ph.D. dissertation. February 2014. Major: Mechanical Engineering. Advisor: Thomas H. Kuehn. 1 computer file (PDF); xiv, 167 pages, appendices A-E.
Viral aerosol survivability, Transmission, and sampling in an environmental chamber.
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