Viruses such as SARS-CoV-2 can be partially shielded from UV radiation when in particles generated by sneezing or coughing: Numerical simulations

Abstract

UV radiation can inactivate viruses such as SARS-CoV-2. However, designing effective UV germicidal irradiation (UVGI) systems can be difficult because the effects of dried respiratory droplets and other fomites on UV light intensities are poorly understood. Numerical modeling of UV intensities inside virus-containing particles on surfaces can increase understanding of these possible reductions in UV intensity. We model UV intensities within spherical approximations of virions randomly positioned within spherical particles. The model virions and dried particles have sizes and optical properties to approximate SARS-CoV-2 and dried particles formed from respiratory droplets, respectively. Wavelengths used are 260 nm (germicidal UVC) and 302 nm (solar UVB). In 5- and 9-μm diameter particles on a surface, illuminated by 260-nm UV light from a direction perpendicular to the surface, 10% and 18% (respectively) of simulated virions are exposed to intensities less than 1/100th of intensities in individually exposed virions (i.e., they are partially shielded). Even for 302-nm light, where the absorption is small, 11% of virions in 9-µm particles have exposures 1/100th those of individually exposed virions. Calculated results show that shielding of virions in a particle can be strongly reduced by illuminating a particle either from multiple widely separated incident directions, or by illuminating a particle rotating in air (because of turbulence, Brownian diffusion, etc.) for a time sufficient to rotate through all orientations with respect to the UV illumination. Because highly UV-reflective paints and surfaces can increase the angular ranges of illumination, they appear likely to be useful for reducing shielding of virions.

Elucidating the role of environmental management of forests, air quality, solid waste and wastewater on the dissemination of SARS-CoV-2

“…Low-cost germicidal UV-C bulbs have been suggested to be installed in higher areas of the room for better air mixing, as their irradiance ranging from 28 - 80 µW cm −2 are likely to reduce 88% airborne SARS-CoV-2 transmissivity within 16 seconds ( Beggs and Avital, 2020 ; Davidson, 2021 ; Nardell 2020; Volchenkov, 2021 ). Even though UV is effective to disinfect indoor air from SARS-CoV-2, its application is recommended in all possible directions to reduce potential infectivity from shielded particles ( Doughty et al, 2021 ; Hill et al, 2021 ). Furthermore, a preprint by Mahammedi and Mahammedi (2020) proposed a solar powered UV mobile disinfectant which can be individualised to specific regions and scales.…”

Design of optical cavity for air sanification through ultraviolet germicidal irradiation

“…In this paper µ is set to 0 since the UV air absorbance can be considered negligible [70, 71]. Also the possible light refraction by the aerosol particles, which would vary the rays path, has not been considered for simplicity, since its effect is quite small when considering air respect to surfaces [72]. The single ray contribution to the volumetric power density p V is: …”

“…Note that the SARS-Cov 2 doses are given for plate measurements. Air sanification could be more effective since light arrives from all directions and also the shading or shielding effects that produce the tail on the lower end of the typical survival fraction curve, which limits higher log inactivation, could disappear [16, 72]. Results from Table 2 point out the directions for the most effective filters, respect to the reference case: high reflectivity, small cavity diameter, optimized source emission angle and longer cavity length.…”