the paradoxical role of far-ultraviolet c (far-uvc) in inactivation of sars-cov-2: the issue of droplet size

The omicron variant is spreading at a rate we have never observed with any previous variant. a lot of efforts have been taken to inactivate sars-cov-2, especially the omicron variant. specific wavelength ranges of electromagnetic radiation can be exploited to inactivate coronaviruses. previous studies show that 222-nm far-ultraviolet c (far-uvc) light inactivates airborne influenza virus efficiently. considering the similar genomic sizes of all human coronaviruses, other human coronaviruses, such as sars-cov-2, would be expected to be inactivated by far-uvc with a similar efficacy. taking this into account, it is concluded that exposure to far-uvc can be introduced as a safe method that significantly reduces the ambient level of airborne coronaviruses in crowded places. biomolecules, particularly proteins, strongly absorb ultraviolet radiation at a wavelength of around 200 nm. given this consideration, far-uvc has a limited ability to permeate biological materials. thus, for example, in only around 0.3 mm of tissue, the intensity of 200-nm uv radiation is decreased by half, compared to tissue penetration of about 3 mm at 250 nm. this paper aims to answer the key question of whether far-uvc can penetrate sars-cov-2 inside inhalable respiratory droplets (with diameters up to 100 μm).