Indoor Air Quality Implications of Germicidal 222 nm Light

GUV Installations Demonstrate Effectiveness and Exposure Safety in Field Settings

Germicidal ultraviolet (GUV) radiation is used in various building types and indoor applications across the U.S. to mitigate the risk of infection from airborne pathogens. However, to date, few studies have evaluated the in situ effectiveness, safety, and occupant's experience with these installations. To address this gap, we developed and applied a protocol for evaluating in situ performance of whole-room (far UV-C) and upper-room GUV installations. Radiometric and electrical measurements were collected characterizing the spectrum, fluence rate, eye and skin exposure, and energy use of 15 installations. Additionally, a questionnaire asked facility managers and occupants about their satisfaction with the GUV installations. Most installations did not exceed time weighted average limits for eye and skin safety. Findings showed that GUV contributed between 3% to 150% toward meeting ASHRAE 241 equivalent clean airflow targets. These findings support further deployment of these GUV technologies to help inactivate airborne pathogens. The GUV system characterization reported in this article can be used to inform GUV system simulation assumptions.

The release of volatile and semi-volatile organic compounds from polyvinyl chloride consumer products under simulated solar light: Implications for indoor air quality

This study investigated the effect of light on emission of various volatile and semi-volatile organic compounds (VOCs and SVOCs), from polyvinyl chloride (PVC) products using xenon lamp as a solar light simulator. The emission flux generally decreased over time, with the light-induced targeted ∑VOC flux being about 1.6-times higher than heat-induced flux during the initial 1-h exposure. The emission is less affected by air flow rate; however, it is increased with light intensity. In general, the ∑SVOC levels are 3-34 times higher than ∑VOC levels. Results indicate that the chemicals released from PVC might decompose into degradation products upon xenon-light irradiation, resulting in intermediate or low-molecular weight compounds. Furthermore, total daily intakes of targeted compounds for different age groups ranged 0.80-29.1 µg/kg/day, while total hazard quotient and cancer risks posed by targeted VOCs ranged 0.020.26; and 4.5 × 10⁻⁶-5.3 × 10⁻⁵, respectively, suggesting the probable risk. Besides, more than 700 peaks are recorded and characterized as non-targeted chemicals. Also, 65-80 % of total number of chemical peaks emitted from PVC are attributed to VOCs, while that for SVOCs is 20-35 %. The fraction of emitted VOC peaks to total peaks under heat and light exposure are found to be 65 and 80 %, respectively. Therefore, indoor air quality can be deteriorated by the presence of PVC-related plastic products.

Influence of Germicidal UV (222 nm) Lamps on Ozone, Ultrafine Particles, and Volatile Organic Compounds in Indoor Office Spaces

Germicidal ultraviolet lamps with a peak emission at 222 nm (GUV222) are gaining prominence as a safe and effective solution to reduce disease transmission in occupied indoor environments. While previous studies have reported O3 production from GUV222, less is known about their impact on other indoor constituents affecting indoor air quality, especially in real occupied environments. In this study, the effects of GUV222 on the levels of ozone (O3), ultrafine particles (UFPs), and volatile organic compounds (VOCs) were investigated across multiple offices with varying occupancies. O3 from the GUV222 operation was observed to increase linearly (∼300 μg h-1 m-1) with a UV light path length from 0 to 3 m beyond which it stabilized. When applied in offices, the O3 production models based on continuous measurements revealed O3 production rates of 1040 ± 87 μg h-1. The resulting increases in steady-state concentrations of 5-21 μg m-3 were highly dependent on the number of office occupants. UFP production occurred during both unoccupied and occupied conditions but predominantly in newly renovated offices. Time-resolved measurements with a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) revealed clear alterations in office VOC concentrations. Unsurprisingly, O3 oxidation chemistry was observed, including monoterpene deprivation and 4-oxopentanal (4-OPA) production. But additionally, significant alterations from unidentified mechanisms occurred, causing increased levels of various PTR-TOF-MS signals including C2H5O2+ and C4H9+ hypothesized to arise from photoinduced formation or off-gassing during the GUV222 lamp operation.

Organic aerosol formation from 222 nm germicidal light: ozone-initiated vs. non-ozone pathways

Germicidal ultraviolet lamps outputting 222 nm light (GUV222) have the potential to reduce the airborne spread of disease through effective inactivation of pathogens, while remaining safe for direct human exposure. However, recent studies have identified these lamps as a source of ozone and other secondary pollutants such as secondary organic aerosol (SOA), and the health effects of these pollutants must be balanced against the benefits of pathogen inactivation. While ozone reactions are likely to account for much of this secondary indoor air pollution, 222 nm light may initiate additional non-ozone chemical processes, including the formation of other oxidants and direct photolytic reactions, which are not as well understood. This work examines the impacts of GUV222 on SOA formation and composition by comparing limonene oxidation under GUV222 and O3-only control conditions in a laboratory chamber. Differences between these experiments enable us to distinguish patterns in aerosol formation driven by ozone chemistry from those driven by other photolytic processes. These experiments also examine the influence of the addition of NO2 and nitrous acid (HONO), and investigate SOA formation in sampled outdoor air. SOA composition and yield vary only slightly with respect to GUV222vs. ozone-only conditions; NO2 and HONO photolysis do not appreciably affect the observed chemistry. In contrast, we observe consistent new particle formation under high-fluence 222 nm light (45 μW cm-2) that differs substantially from ozone-only experiments. This observed new particle formation represents an additional reason to keep GUV222 fluence rates to the lowest effective levels.

Human exposure to air contaminants under the far-UVC system operation in an office: effects of lamp position and ventilation condition

The far-UVC (222 nm) system has emerged as a solution for controlling airborne transmission, yet its effect on indoor air quality, particularly concerning positioning, remains understudied. In this study, we examined the impact of far-UVC lamp position on the disinfection and secondary contaminant formation in a small office. We employed a three-dimensional computational fluid dynamics (CFD) model to integrate UV intensity fields formed by different lamp positions (ceiling-mounted, wall-mounted, and stand-alone types) along with the air quality model. Our findings reveal that the ceiling-mounted type reduces human exposure to airborne pathogens by up to 80% compared to scenarios without far-UVC. For all the lamp positions, O3 concentration in the breathing zone increases by 4-6 ppb after one hour of operation. However, it should be noted that a high concentration zone (> 25 ppb) forms near the lamp when it is turned on. Moreover, ventilation plays a crucial role in determining human exposure to airborne pathogens and secondary contaminants. Increasing the ventilation rate from 0.7 h-1 to 4 h-1 reduces airborne pathogen and secondary contaminant concentrations by up to 90%. However, caution is warranted as higher ventilation rates can lead to elevated O3 indoors, especially under conditions of high outdoor O3 concentrations.

The public-health significance of far-UVC-induced indoor ozone and its associated secondary chemistry

There has been much recent interest in whole-room far-UVC (wavelength around 222 nm) to markedly and safely reduce overall levels of airborne pathogens in occupied indoor locations. Far-UVC light produces very low levels of ozone-in real-world scenarios induced ozone levels of less than 10 ppb, and much less in moderately or well-ventilated rooms compliant with US far-UVC dose recommendations, and very much less in rooms compliant with international far-UVC dose standards. At these very low ozone levels, there is no epidemiological evidence of increased health risks from any of the very large outdoor ozone studies, whether from ozone alone or from ozone plus associated pollutants. Indoors, at the low ozone concentrations of relevance here, ozone does not react rapidly enough with preexisting airborne volatile organic compounds to compete with even extremely low levels of room ventilation, so significant ozone-induced ultrafine particle production is very unlikely. Direct measurements in real-life room scenarios are consistent with these conclusions. A potential exception is the cleaning material limonene, which has an unusually high ozone interaction cross-section; in the far-UVC context, turning off far-UVC lights during cleaning with limonene products would be reasonable.

Effects of 222 nm Germicidal Ultraviolet Light on Aerosol and VOC Formation from Limonene

Since the 1930s, germicidal ultraviolet (GUV) irradiation has been used indoors to prevent the transmission of airborne diseases, such as tuberculosis and measles. Recently, it has received renewed attention due to the COVID-19 pandemic. While GUV radiation has been shown to be effective in inactivating airborne bacteria and viruses, few studies on the impact of GUV on indoor air quality have been published. In this work, we evaluate the effects of GUV222 (GUV at 222 nm) on the chemistry of a common indoor volatile organic compound (VOC), limonene. We found that the production of O3 by the GUV222 lamps caused the formation of particulate matter (PM) and oxygenated volatile organic compounds (VOCs). We also found that the chemistry proceeds through the ozonolysis of limonene as well as the reaction with secondary OH, and that the presence of GUV light led to observable but small perturbations to this chemistry. Understanding the effects of GUV222 on indoor air quality is important in evaluating the safety of these devices.

Formation and Transport of Secondary Contaminants Associated with Germicidal Ultraviolet Light Systems in an Occupied Classroom

Germicidal ultraviolet light (GUV) systems are designed to control airborne pathogen transmission in buildings. However, it is important to acknowledge that certain conditions and system configurations may lead GUV systems to produce air contaminants including oxidants and secondary organic aerosols (SOA). In this study, we modeled the formation and dispersion of oxidants and secondary contaminants generated by the operation of GUV systems employing ultraviolet C 254 and 222 nm. Using a three-dimensional computational fluid dynamics model, we examined the breathing zone concentrations of chemical species in an occupied classroom. Our findings indicate that operating GUV 222 leads to an approximate increase of 10 ppb in O3 concentration and 5.2 μg·m-3 in SOA concentration compared to a condition without GUV operation, while GUV 254 increases the SOA concentration by about 1.2 μg·m-3, with a minimal impact on the O3 concentration. Furthermore, increasing the UV fluence rate of GUV 222 from 1 to 5 μW·cm-2 results in up to 80% increase in the oxidants and SOA concentrations. For GUV 254, elevating the UV fluence rate from 30 to 50 μW·cm-2 or doubling the radiating volume results in up to 50% increase in the SOA concentration. Note that indoor airflow patterns, particularly buoyancy-driven airflow (or displacement ventilation), lead to 15-45% lower SOA concentrations in the breathing zone compared to well-mixed airflow. The results also reveal that when the ventilation rate is below 2 h-1, operating GUV 254 has a smaller impact on human exposure to secondary contaminants than GUV 222. However, GUV 254 may generate more contaminants than GUV 222 when operating at high indoor O3 levels (>15 ppb). These results suggest that the design of GUV systems should consider indoor O3 levels and room ventilation conditions.

On the Use of the Intrinsic DNA Fluorescence for Monitoring Its Damage: A Contribution from Fundamental Studies

The assessment of DNA damage by means of appropriate fluorescent probes is widely spread. In the specific case of UV-induced damage, it has been suggested to use the emission of dimeric photoproducts as an internal indicator for the efficacy of spermicidal lamps. However, in the light of fundamental studies on the UV-induced processes, outlined in this review, this is not straightforward. It is by now well established that, in addition to photodimers formed via an electronic excited state, photoionization also takes place with comparable or higher quantum yields, depending on the irradiation wavelength. Among the multitude of final lesions, some have been fully characterized, but others remain unknown; some of them may emit, while others go undetected upon monitoring fluorescence, the result being strongly dependent on both the irradiation and the excitation wavelength. In contrast, the fluorescence of undamaged nucleobases associated with emission from ππ* states, localized or excitonic, appearing at wavelengths shorter than 330 nm is worthy of being explored to this end. Despite its low quantum yield, it is readily detected nowadays. Its intensity decreases due to the disappearance of the reacting nucleobases and the loss of exciton coherence provoked by the presence of lesions, independently of their type. Thus, it could potentially provide valuable information about the DNA damage induced, not only by UV radiation but also by other sanitizing or therapeutic agents.

Ozone generation and chemistry from 222 nm germicidal ultraviolet light in a fragrant restroom

Devices using 222 nm germicidal ultraviolet light (GUV222) have been marketed to reduce virus transmission indoors with low risk of occupant harm from direct UV exposure. GUV222 generates ozone, an indoor air pollutant and oxidant, under constrained laboratory conditions, but the chemistry byproducts of GUV222-generated ozone in real indoor spaces is uncharacterized. We deployed GUV222 in a public restroom, with an air change rate of 1 h-1 one weekend and 2 h-1 the next, to measure ozone formation and byproducts generated from ozone chemistry indoors. Ozone from GUV222 increased background concentrations by 5 ppb on average for both weekends and reacted rapidly (e.g., at rates of 3.7 h-1 for the first weekend and 2.0 h-1 for the second) with gas-phase precursors emitted by urinal screens and on surfaces. These ozone reactions generated volatile organic compound and aerosol byproducts (e.g., up to 2.6 μg m-3 of aerosol mass). We find that GUV222 is enhancing indoor chemistry by at least a factor of two for this restroom. The extent of this enhanced chemistry will likely be different for different indoor spaces and is dependent upon ventilation rates, species and concentrations of precursor VOCs, and surface reactivity. Informed by our measurements of ozone reactivity and background aerosol concentrations, we present a framework for predicting aerosol byproduct formation from GUV222 that can be extended to other indoor spaces. Further research is needed to understand how typical uses of GUV222 could impact air quality in chemically diverse indoor spaces and generate indoor air chemistry byproducts that can affect human health.

Quantification of Byproduct Formation from Portable Air Cleaners Using a Proposed Standard Test Method

In response to the COVID-19 pandemic, air cleaning technologies were promoted as useful tools for disinfecting public spaces and combating airborne pathogen transmission. However, no standard method exists to assess the potentially harmful byproduct formation from air cleaners. Through a consensus standard development process, a draft standard test method to assess portable air cleaner performance was developed, and a suite of air cleaners employing seven different technologies was tested. The test method quantifies not only the removal efficiency of a challenge chemical suite and ultrafine particulate matter but also byproduct formation. Clean air delivery rates (CADRs) are used to quantify the chemical and particle removal efficiencies, and an emission rate framework is used to quantify the formation of formaldehyde, ozone, and other volatile organic compounds. We find that the tested photocatalytic oxidation and germicidal ultraviolet light (GUV) technologies produced the highest levels of aldehyde byproducts having emission rates of 202 and 243 μg h-1, respectively. Additionally, GUV using two different wavelengths, 222 and 254 nm, both produced ultrafine particulate matter.

Reducing Transmission of Airborne Respiratory Pathogens: A New Beginning as the COVID-19 Emergency Ends

BACKGROUND

In response to the COVID-19 pandemic, new evidence-based strategies have emerged for reducing transmission of respiratory infections through management of indoor air.

OBJECTIVES

This paper reviews critical advances that could reduce the burden of disease from inhaled pathogens and describes challenges in their implementation.

DISCUSSION

Proven strategies include assuring sufficient ventilation, air cleaning by filtration, and air disinfection by germicidal ultraviolet (UV) light. Layered intervention strategies are needed to maximize risk reduction. Case studies demonstrate how to implement these tools while also revealing barriers to implementation. Future needs include standards designed with infection resilience and equity in mind, buildings optimized for infection resilience among other drivers, new approaches and technologies to improve ventilation, scientific consensus on the amount of ventilation needed to achieve a desired level of risk, methods for evaluating new air-cleaning technologies, studies of their long-term health effects, workforce training on ventilation systems, easier access to federal funds, demonstration projects in schools, and communication with the public about the importance of indoor air quality and actions people can take to improve it. https://doi.org/10.1289/EHP13878.

Pentagon Found Daily, Metagenomic Detection of Novel Bioaerosol Threats to Be Cost-Prohibitive: Can Virtualization and AI Make It Cost-Effective?

In 2022, the Pentagon Force Protection Agency found threat agnostic detection of novel bioaerosol threats to be "not feasible for daily operations" due to the cost of reagents used for metagenomics, cost of sequencing instruments, and cost of labor for subject matter experts to analyze bioinformatics. Similar operational difficulties might extend to many of the 280,000 buildings (totaling 2.3 billion square feet) at 5,000 secure US Department of Defense military sites, 250 Navy ships, as well as many civilian buildings. These economic barriers can still be addressed in a threat agnostic manner by dynamically pooling samples from dry filter units, called spike-triggered virtualization, whereby pooling and sequencing depth are automatically modulated based on novel biothreats in the sequencing output. By running at a high average pooling factor, the daily and annual cost per dry filter unit can be reduced by 10 to 100 times depending on the chosen trigger thresholds. Artificial intelligence can further enhance the sensitivity of spike-triggered virtualization. The risk of infection during the 12- to 24-hour window between a bioaerosol incident and its detection remains, but in some cases it can be reduced by 80% or more with high-speed indoor air cleaning exceeding 12 air changes per hour, which is similar to the rate of air cleaning in passenger airplanes in flight. That level of air changes per hour or higher is likely to be cost-prohibitive using central heating ventilation and air conditioning systems, but it can be achieved economically by using portable air filtration in rooms with typical ceiling heights (less than 10 feet) for a cost of approximately $0.50 to $1 per square foot for do-it-yourself units and $2 to $5 per square foot for high-efficiency particulate air filters.

Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm

Recent interest in commercial devices containing germicidal ultraviolet lamps with a peak emission wavelength at 222 nm (GUV222) has focused on mitigating virus transmission indoors while posing minimum risk to human tissue. However, 222 nm light can produce ozone (O3) in air. O3 is an undesirable component of indoor air because of health impacts from acute to chronic exposure and its ability to degrade indoor air quality through oxidation chemistry. In seven four-hour experiments we measured O3 produced from a single filtered GUV222 lamp in a 31.5 m3 stainless steel chamber. Using an emission model, we determined an O3 generation rate of 19.4 ppbv h-1 ± 0.3 ppbv h-1 (equivalent to 1.22 mg h-1 ± 0.02 mg h-1). We estimated the fluence rate from the lamp using two methods: (1) chemical actinometry using tetrachloroethylene (actinometry) and (2) geometric projection of the irradiance field from radial and angular distribution measurements of the GUV222 lamp fluence (irradiance). Using the estimated lamp fluence rates of 2.2 μW cm-2 (actinometry) and 3.2 μW cm-2 (irradiance) we predicted O3 production in our chamber within 20 % of the average measured mixing ratio. Future studies should evaluate the indoor air quality impacts of GUV222 technologies.