ABSTRACT
UVB in sunlight, 290-315 nm, can inactivate SARS CoV and SARS CoV-2 viruses on surfaces and in the air. Laboratory exposure to ultraviolet irradiance in the UVC range inactivates many viruses and bacteria in times less than 30 min. Estimated UVB inactivation doses from sunlight in J/m2 are obtained from UVC measurements and radiative transfer calculations, weighted by a virus inactivation action spectrum, using OMI satellite atmospheric data for ozone, clouds, and aerosols. For SARS CoV, using an assumed UVC dose near the mid-range of measured values, D 90 = 40 J/m2, 90% inactivation times T 90 are estimated for exposure to midday 10:00-14:00 direct plus diffuse sunlight and for nearby locations in the shade (diffuse UVB only). For the assumed D 90 = 40 J/m2 model applicable to SARS CoV viruses, calculated estimates show that near noon 11:00-13:00 clear-sky direct sunlight gives values of T 90 < 90 min for mid-latitude sites between March and September and less than 60 min for many equatorial sites for 12 months of the year. Recent direct measurements of UVB sunlight inactivation of the SARS CoV-2 virus that causes COVID-19 show shorter T 90 inactivation times less than 10 min depending on latitude, season, and hour. The equivalent UVC 254 nm D 90 dose for SARS CoV-2 is estimated as 3.2 ± 0.7 J/m2 for viruses on a steel mesh surface and 6.5 ± 1.4 J/m2 for viruses in a growth medium. For SARS CoV-2 clear-sky T 90 on a surface ranges from 4 min in the equatorial zone to less than 30 min in a geographic area forming a near circle with solar zenith angle < 60O centered on the subsolar point for local solar times from 09:00 to 15:00 h.