AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
UV Intensity Calculated in Clusters of Spores Held on Surfaces for Models of the Effects of UV on Viability
STEVEN HILL, Dan Mackowski, David Doughty, CCDC Army Research Laboratory
Abstract Number: 671 Working Group: Bioaerosols
Abstract Ultraviolet (UV) light can inactivate bacteria and their spores. Bacteria in agglomerate particles can be partially protected from solar UV, an observation that may explain the increased fraction of atmospheric bacteria associated with larger particles near mid-day. There is a need for increased quantitative understanding of the effects of solar UV and germicidal UV on bacteria in the air or on surfaces. Bacterial spores withstand the effects of UV and other environmental hazards better than vegetative cells. We have mathematically modeled bacterial spores as homogeneous spheres, and calculated UV intensities within illuminated individual spheres and clusters of these spheres using the multi-sphere T-matrix (MSTM) method. The simulated cluster can be held within a sphere which encompasses the spheres of the cluster and fills the spaces between them. This encompassing sphere may be given any appropriate complex refractive index. In our previous calculations, the non-rotating clusters, held in fixed position to simulate clusters on a surface, were not in contact with a simulated surface. In nature, contact with a surface is needed to hold the cluster in fixed position. Because actual physical surfaces reflect light, the question of the effects of the surface on the UV intensities within the cluster has not been treated. To address this problem, the MSTM has been extended to calculate UV intensities within clusters on surfaces. The resulting calculations indicate that the effects of the surface on the UV intensity tend to be largest in the spheres closest to the surface, and are especially large in the spheres with most protection from the UV. Also, the effects of the surface are largest for surfaces with higher absorptivity, for the ranges of complex refractive indexes of the spores and surfaces studied here.