Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps

Abstract

Air disinfection using germicidal ultraviolet light (GUV) has received increasing attention during the COVID-19 pandemic. GUV uses UVC lamps to inactivate microorganisms, but it also initiates photochemistry in air. However, GUV's indoorair-quality impact has not been investigated in detail. Here, we model the chemistry initiated by GUV at 254 ("GUV254") or 222 nm ("GUV222") in a typical indoor setting for different ventilation levels. Our analysis shows that GUV254, usually installed in the upper room, can significantly photolyze O 3 , generating OH radicals that oxidize indoor volatile organic compounds (VOCs) into more oxidized VOCs. Secondary organic aerosol (SOA) is also formed as a VOC-oxidation product. GUV254-induced SOA formation is of the order of 0.1−1 μg/m 3 for the cases studied here. GUV222 (described by some as harmless to humans and thus applicable for the whole room) with the same effective virus-removal rate makes a smaller indoor-air-quality impact at mid-to-high ventilation rates. This is mainly because of the lower UV irradiance needed and also less efficient OH-generating O 3 photolysis than GUV254. GUV222 has a higher impact than GUV254 under poor ventilation due to a small but significant photochemical production of O 3 at 222 nm, which does not occur with GUV254.

Significant Production of Ozone from Germicidal UV Lights at 222 nm

“…O 3 itself is a major air pollutant causing excess deaths at levels below those in occupational guidelines of 50–100 ppb. , More importantly, it can also lead to formation of other pollutants including particulate matter, whose excess death impacts can be many times higher than those of O 3 itself (section S6). , O 3 production by GUV222 lamps thus can be a major concern, at least under low-ventilation conditions.…”

“…A recent review concluded that O 3 generation by KrCl excimer lamps was minimal: for example, a 12 W lamp was estimated to take 267 h to produce 4.5 ppb O 3 in a 30 m 3 room in the absence of losses . A recent modeling paper estimated O 3 generation to be nearly two orders of magnitude faster, but those findings have not been confirmed experimentally. There is also discussion in the literature whether O 3 is mainly formed by the UVC radiation or by discharges in electrical connections …”

Oxygen Effect on the Ultraviolet-C Photochemistry of Lactic Acid

“…As discussed previously, UVC has been used as a sterilization method in hospitals due to its germicidal effects and ability to deactivate some viruses. − Moreover, with the recent Coronavirus Disease 2019 (COVID-19) pandemic, UVC disinfection systems have seen a spike in sales, necessitating further studies for the safe usage of UVC radiation. Many of the safety studies performed to date have focused on the impact of direct radiation on DNA. ,, However, recent studies − and the work presented here shows that safety studies should also consider secondary reactions caused by UVC irradiation of organic molecules, including those resulting from human emissions in indoor environments.…”

“…). − ,, As mentioned previously, lactic acid is prevalent in indoor environments due to human emissions, where it will likely be found on surfaces or in aerosols due to its low vapor pressure. , We therefore suggest that lactic acid photolysis may be occurring in such indoor environments and could produce harmful byproducts during these UVC sterilization procedures. However, most photochemical studies address photochemistry in the modern Earth’s outdoor environment where UVC is not available, and thus, few studies have addressed photochemistry using radiation with energies equal to UVC sterilization procedures. − Previous work by Deal et al and others ,, suggests that lactic acid may be photoactive under these conditions and, if so, will produce harmful byproducts (e.g., CO and formic acid) that may remain even after the UVC sterilization is complete, thereby posing an indirect risk to human health. It is therefore important to understand the products and mechanisms of lactic acid photolysis in environments which more accurately model indoor environments (i.e., in the presence of oxygen).…”

The World Is Completely Unprepared For Detecting Emerging Viruses/Bacteria In The Air

“…GUV has been in use in many applications across DoD [73], in hospitals for infection control and to some extent for short-term or temporary exposure in public spaces. At this time a debate remains unresolved about long-term safety and appropriateness for extended, daily use of GUV [58] especially in regards to excessive generation of volatile organic compounds (VOC) and formation of secondary aerosols [59] [60] which may be carcinogenic [61]. 4 is used to estimate the combination effect on reduction of infectious particle concentration (P2P contagion) using both 24x7x365 detection with 12 ACH air filtration in the room (Figure 8).…”