A Model for Inactivation of Microbes Suspended in the Atmosphere by Solar Ultraviolet Radiation

Abstract

Solar ultraviolet (UV) light within 280-320 nm (UVB) is the primary cause for virus inactivation in the atmosphere. Only the effect of the direct component has been previously evaluated. We developed a simple regression model to estimate the inactivation of a virus due to direct (unscattered), diffuse (scattered) and total (direct + diffuse) components of solar UV (daily integrated irradiances). The model predicts the maximum number of radiation-days a virus will survive at a given altitude above the ground in rural and urban environments under clear skies. We explored the effect of several environmental variables: visibility, altitude and ground reflectivity. We found that the effect of diffuse radiation on virus inactivation was larger than the direct component. The diffuse irradiance increased with ground albedo (mainly due to reflection of the direct attenuated solar off the ground) and decreased with increased visibility (proportional to aerosol loading in the atmosphere). The diffuse component increased with altitude, but the ratio of diffuse to the total decreased with increased altitude, highlighting the importance of the diffuse component of UV near the ground. Our model may help public health studies in predicting and understanding the effect of environmental parameters on the survival of germs.

Regression Model for Estimating Inactivation of Microbial Aerosols by Solar Radiation

“…were determined by least‐square fit of the nine quantities calculated by MODTRAN data corresponding to the 1976 U.S. Standard atmosphere and a midlatitude atmosphere at two different seasons (spring–summer and fall–winter) and for two ambient aerosols models (for urban and rural environments), at the dates of the two solstices and the two equinox dates. We previously reported that plane irradiances calculated by MODTRAN underestimated spherical actinic irradiances . Therefore, Eq.…”

“…2 in ref. ). We developed a regression model for three atmospheres; the 1976 US Standard and two midlatitude atmospheres.…”

“…Although the action spectrum was built using D 37 values measured at various wavelengths, other survival levels can also be employed, e.g . the survival levels for 1 − log 10 or 2 − log 10 are 10% and 1%, respectively . Microbial survival can thus be estimated by combining the microbial sensitivities that have been measured or estimated previously (, reviewed in ) with the atmospheric radiances calculated by the method described here for aerosols suspended at different altitudes under various conditions.…”

“…S7): (total, diffuse and direct ambient fluxes at noon), and E dir (ambient direct daily energy). An example of using and to estimate the maximum number of days necessary to inactivate influenza virus in aerosols suspended at midlatitude under a specific set of atmospheric conditions has been previously described with a discussion of the difference between spherical actinic fluxes and MODTRAN plane radiances. In this work all radiation quantities (energy and flux) are for radiation on horizontal plane ( i.e .…”

Inactivation of Vaccinia Virus by Natural Sunlight and by Artificial UVB Radiation

“…It should be noted that essentially only direct solar radiation was measured because of the baffled construction of the spectroradiometer detector, i.e ., little indirect, scattered radiation from the sky reached that detector. As indirect radiation accounts for nearly half the total solar radiation reaching the earth , the actual UVB output of the solar simulator is only 4–5 times higher than the total sun irradiance, rather than the 10 times factor applied to overlap both spectra as shown in Fig. .…”