Shielding of viruses such as SARS-Cov-2 from ultraviolet radiation in particles generated by sneezing or coughing: Numerical simulations of survival fractions

Abstract

SARS-CoV-2 and other microbes within aerosol particles can be partially shielded from UV radiation. The particles refract and absorb light, and thereby reduce the UV intensity at various locations within the particle. Previously we demonstrated shielding in calculations of UV intensities within spherical approximations of SARS-CoV-2 virions within spherical particles approximating dried-to-equilibrium respiratory fluids. The purpose of this paper is to extend that work to survival fractions of virions (i.e., fractions of virions that can infect cells) within spherical particles approximating dried respiratory fluids, and to investigate the implications of these calculations for using UV light for disinfection. The particles may be on a surface or in air.Here, the survival fraction (S) of a set of individual virions illuminated with a UV fluence (F, in J/m 2 ) is assumed described by S(kF)=exp(-kF), where k is the UV inactivation rate constant (m 2 /J). The average survival fraction (S p ) of the simulated virions in a group of particles is calculated using the energy absorbed by each virion in the particles. The results show that virions within particles of dried respiratory fluids can have larger S p than do individual virions.For individual virions, and virions within 1-, 5-, and 9-µm particles illuminated (normal A c c e p t e d M a n u s c r i p t incidence) on a surface with 260-nm UV light, the S p = 0.00005, 0.0155, 0.22 and 0.28, respectively, when kF=10. The S p decrease to <10 -7 , <10 -7 , 0.077 and 0.15, respectively, for kF=100. Results also show that illuminating particles with UV beams from widely separated directions can strongly reduce the S p . These results suggest that the size distributions and optical properties of the dried particles of virion-containing respiratory fluids are likely important to effectively designing and using UV germicidal irradiation systems for microbes in particles. The results suggest the use of reflective surfaces to increase the angles of illumination and decrease the S p . The results suggest the need for measurements of the S p of SARS-CoV-2 in particles having compositions and sizes relevant to the modes of disease transmission.

Retracted: Evaluating the effects of air disinfectants in decontamination of COVID‐19 aerosols

“…UVC efficacy ranges from 36.4% to 100%. 29 , 30 , 34 , 48 , 60 , 61 Efficacy variability is attributed to the mode of usage as reported by the studies. 30 , 45 …”

“…The findings of the present review show that UVC is the most common method used in disinfecting objects mostly N95 masks, contaminated air, and other contact objects with the possibility of viral contamination. UVC efficacy ranges from 36.4% to 100% 29,30,34,48,60,61 . Efficacy variability is attributed to the mode of usage as reported by the studies 30,45 …”

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.…”

Accurate Measurement of the Optical Properties of Single Aerosol Particles Using Cavity Ring-Down Spectroscopy

“…In healthcare applications, the optical properties of pathogen-containing droplets may influence pathogen survival rates upon droplet exposure to UV germicidal radiation. 19 , 20 UV absorption measurements of such droplets could contribute to the development of improved sterilization technologies. Progress toward these and other impacts requires new spectroscopic tools that can track changes in composition using measurements of light absorption to unravel the fundamental chemical, physical, and biological processes at work in aerosol particles.…”

“…Recent demonstrations of accelerated reactions in micron-scale droplets offer new avenues for sustainable chemical synthesis, but the reasons for significantly enhanced reaction rates remain the subject of intensive investigation. − A newfound ability to monitoring changes in chemical composition of micron-scale single aerosol particles using absorption spectroscopy may help to unravel these causes. In healthcare applications, the optical properties of pathogen-containing droplets may influence pathogen survival rates upon droplet exposure to UV germicidal radiation. , UV absorption measurements of such droplets could contribute to the development of improved sterilization technologies. Progress toward these and other impacts requires new spectroscopic tools that can track changes in composition using measurements of light absorption to unravel the fundamental chemical, physical, and biological processes at work in aerosol particles.…”