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

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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) with the air quality model. Our findings reveal that the ceiling-mounted type reduces human exposure to airborne pathogens by up to 80%. For all the lamp positions, the O 3 concentration in the breathing zone increases by 4–6 ppb after one hour of operation. However, the stand-alone type poses a risk of exposing occupants to elevated levels of O 3 , as it creates a high concentration zone (> 25 ppb) near the lamp. 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 it could also lead to elevated O 3 indoors, particularly in high outdoor O 3 conditions. Earth and environmental sciences/Environmental sciences Physical sciences/Chemistry Physical sciences/Engineering Physical sciences/Mathematics and computing Indoor air quality COVID-19 secondary chemistry ozone germicidal ultraviolet UVC 222 nm Figures Figure 1 Figure 2 Introduction In the wake of the novel coronavirus (COVID-19) outbreak, the germicidal ultraviolet (GUV) system has emerged as a prominent solution for effectively controlling airborne pathogens. Traditionally, ultraviolet C (UVC) at 254 nm has been used to irradiate the upper section of rooms, primarily due to its known adverse effects on human skin cells. [ 1 – 3 ]. In recent times, there has been a growing preference for utilizing shorter wavelengths, known as far-UVC, which involves KrCl excimer lamps emitting UVC at a peak wavelength of 222 nm [ 4 , 5 ]. Far-UVC has demonstrated the capability to deactivate airborne pathogens by degrading their genetic material and impeding their reproductive capacity [ 6 – 11 ]. Notably, its minimal impact on human tissues positions it as a viable method for comprehensive indoor disinfection [ 7 , 12 , 13 ]. However, concerns have been raised regarding the potential of the far-UVC system to serve as an indoor O 3 source [ 14 – 18 ]. The photolysis of O 2 by the wavelength range of 175–242 nm, inherent to this system, results in O 3 generation. While O 3 itself poses risks, it also instigates indoor chemical reactions, leading to the formation of air pollutants such as oxidants and secondary organic aerosols (SOA) [ 14 , 18 – 21 ]. The market offers various configurations of far-UVC lamps, including ceiling-mounted, wall-mounted, and stand-alone types. Given a high UV intensity near the lamp that rapidly decreases with distance, the positioning of the far-UVC lamp significantly affects the distribution of UV intensity within a space [ 15 , 22 , 23 ]. This distribution can not only impact the removal efficiency of pathogens but also influence the rate constant of O 2 photolysis by UVC at 222 nm [ 4 , 15 ]. Therefore, the placement of the far-UVC system is intricately linked to human exposure to airborne pathogens and secondary contaminants. In this study, we investigate detailed airborne pathogen disinfection and indoor O 3 chemistry due to far-UVC system within an office environment, based on a computational fluid dynamics (CFD) simulation. By examining impacts of six different positions of the far-UVC lamp under four ventilation conditions, our investigation elucidates the implications of far-UVC lamps for human exposure to airborne pathogens and secondary contaminants. Methods We conducted simulations to analyze the disinfection of airborne pathogens and secondary contaminant formation associated with the far-UVC system operation. These simulations were carried out using the commercial CFD solver STAR-CCM+ (version 2021.03) [ 24 ]. In the CFD model, airborne pathogen and chemical reactions were modeled simultaneously. The Eulerian model was employed to simulate airborne pathogens, whereas the multi-component gas model was utilized for modeling chemical reactions. We created the simulation domain with dimensions of 7.0 m × 5.8 m × 3.1 m (length × width × height) and included four occupants (see Figure S1 ) based on the experimental setup outlined by Liu et al. (2022) [ 25 ]. Given that the highest airborne pathogen concentration occurred when the occupant 4 (P4) was infected and speaking (see Figure S7), we designated P4 as a constant source of airborne pathogens. Specifically, P4 continuously emitted airborne pathogens from a 1.2 cm 2 mouth opening with an air speed of 4 m∙s − 1 in a horizontal direction [ 26 – 28 ]. The size of airborne pathogens emitted from the infector’s mouth was set to 1 µm with a density of 1000 kg∙m − 3 , based on the dominant droplet size for the talking mode [ 27 , 29 ]. The emission concentration was maintained at 1 µg∙m 3 . Airborne pathogens were then removed by ventilation and deposition onto the floor with a deposition velocity of 0.003 cm∙s − 1 [ 30 ]. The susceptibility constant of airborne pathogens to UVC at 222 nm was set to 1.4 × 10 − 3 cm 2 ∙µW − 1 ∙s − 1 , simulating SARS-CoV-2 [ 13 ]. Each occupant generates a metabolic heat of 99W in seating mode [ 31 ]. Chemical reactions associated with far-UVC system were modeled based on Barber et al. (2023) [ 15 ], incorporating a total of 12 chemical reactions in the CFD simulation (see Table S1 ). In the chemistry simulation, we assumed that there was no indoor O 3 source and no UV radiation through windows. The outdoor O 3 concentration was set to 40 ppb, considering typical urban environments [ 32 ]. Indoor O 3 was removed from room surfaces at a deposition rate of 2.8 h − 1 [ 33 ] and from human surfaces at a deposition velocity of 6.8 h − 1 [ 20 ]. Assuming a typical indoor condition, the VOCs emission rates from indoor surfaces and occupants were set at 150 µg∙m − 2 ∙h − 1 and 1 µg∙s − 1 ∙person − 1 , respectively [ 34 , 35 ]. Note that all chemical reactions occur under atmospheric conditions of 1 atm pressure, a relative humidity ranging from 35–40%, and a temperature of 298 K, which are typical indoor conditions at sea level. Further details regarding boundary conditions and the CFD simulation setup can be found in Sections S1 and S2 of the Supporting Information. To investigate the effect of the far-UVC lamp position relative to the occupant area, we modeled six different positions (Fig. 1 ): ceiling-mounted type, wall-mounted type, and stand-alone type 1–4. The ceiling-mounted far-UVC lamp emits a 120-degree beam, while other types produce a beam in all directions. The power of each lamp was adjusted to achieve the room average UV fluence rate of 3 µW∙cm − 2 [ 15 – 17 ], and the spatial distributions of UV fluence rates were obtained using the Visual Software [ 36 ]. The average UV fluence rate within the human envelope zone of all lamp types remains below 1.1 µW∙cm − 2 , meeting the eye exposure limit standards set by the American Conference of Governmental Industrial Hygienists (ACGIH) eye limit (0.3–1.5 µW∙cm − 2 ) [ 17 ]. Note that the human envelope zone is defined as a 0.8 m 3 box air volume near the human body (see Figure S8) [ 20 ]. Along with six lamp positions, four distinct ventilation conditions were examined: mixing ventilation at rates of 0.7 h − 1 , 2 h − 1 , and 4 h − 1 , and infiltration at a rate of 0.7 h − 1 . Note that the 0.7 h − 1 is the minimum requirements by ASHRAE [ 37 ], and 4 h − 1 is considered good by The Lancet COVID-19 commission [ 38 ]. To enhance the credibility of our CFD model, we conducted validation exercises to assess its ability to predict airborne transmission and indoor chemical reactions. Specifically, we validated the airflow field and particle transport within a room, the time-series airborne pathogen concentrations, O 3 generation by indoor chemical reactions, and O 3 deposition were validated by comparing the CFD result with the experimental data and well-mixed mass balance model. Further details on the CFD model validation can be found in Section S3. To analyze the infection risk related to the inhalation of airborne pathogens, we used a metric “intake faction” within the ASHRAE breathing zone and the human breathing box for one hour (Eq. 1) [ 27 ]. Note that the ASHRAE breathing zone is defined as the air volume extending from 8 cm to 180 cm above 60 cm away from walls [ 37 ], and the human breathing box is defined as a 500 cm 3 air volume below the nose tip) [ 39 ]. \(Intake fraction= \frac{{\int }_{0}^{T}{Q}_{b}C\left(t\right)dt}{{\int }_{0}^{T}E\left(t\right)dt}\) Eq. 1 Where, \({Q}_{b}\) is the breathing flow rate of occupants (rest mode − 0.6 m 3 ∙h − 1 ) [ 27 ], \(C\left(t\right)\) is the contaminant concentration, \(E\left(t\right)\) is the emission rate, and \(T\) is the total emission time. Similarly, we presented the results of O 3 , OH, and products as a one-hour integrated exposure within the ASHRAE breathing zone and the human breathing box (Eq. 2). \(Exposure= {\int }_{0}^{T}tC\left(t\right)dt\) Eq. 2 Results and discussion Airborne pathogen transmission Figures 2 a, b, c, and d illustrate the intake fraction within the ASHRAE breathing zone over one hour under four different ventilation conditions. Details of the airborne pathogen distributions at one hour are provided in Figures S9 and S10. Far-UVC systems demonstrate a reduction in airborne pathogen concentration by 50–85% after one hour (see Figure S11), resulting in 40–80% decreases in 1-h human exposure. Notably, while stand-alone types exhibit a higher UV fluence rate within the breathing zone, the ceiling-mounted type shows a more pronounced reduction effect across all types. Specifically, at a ventilation rate of 0.7 h − 1 , the ceiling-mounted type lowers the intake fraction from 2.12 to 0.46 under mixing ventilation and from 2.24 to 0.63 under the infiltration condition. This is mainly because airborne pathogens emitted from an infector tend to ascend with the room airflow, reaching the upper region close to a far-UVC lamp on the ceiling (Figure S12). Meanwhile, the wall-mounted type yields a 60–70% higher intake fraction than the ceiling-mounted type. The notable difference is attributed to the ceiling-mounted type creating a higher UV fluence rate than the wall-mounted type within both the breathing zone and upper region of the room, where airborne pathogens accumulate under the effects of occupant thermal plumes. The reduction effect of stand-alone types is less than that of the ceiling-mounted type and varies with position and ventilation conditions. For example, type 1 (closest to the infector) consistently shows the highest reduction under mixing ventilation, while, under infiltration, types 3 (3 m away from the infector) yield the lowest intake fraction. In addition to the positioning of far-UVC systems, ventilation conditions play a crucial role in determining human exposure to airborne pathogens. Increased ventilation not only dilutes airborne pathogens but also influences personal exposure, as reflected by the intake fraction within the breathing box. When the ventilation rate is 0.7 h − 1 under mixing ventilation, P1 (facing the infector, P4) is exposed to airborne pathogens more than two times higher than P2 and P3 (see Fig. 2 a). Under infiltration, the intake fraction within the breathing box for P1 exceeds those of P2 and P3 by up to ninefold (Fig. 2 d). This is primarily due to the reduced air mixing effect under infiltration, allowing the air jet emitted from the infector's mouth to travel a longer distance toward the occupant positioned directly in front of the infector [ 2 , 28 , 41 ]. On the other hand, at ventilation rates of 2 h − 1 and 4 h − 1 , the increased air mixing effect results in relatively uniform exposure to airborne pathogens among all occupants (see Figs. 2 b and c). This finding suggests that higher ventilation rates can help reduce human exposure to airborne pathogens and also ensure equal protection for all occupants. Exposure to secondary contaminants Figures 2 e, f, g, and h illustrate 1-h human exposure to O 3 within the ASHRAE breathing zone under four different ventilation conditions. Detailed O 3 concentration contours at one hour for all conditions are provided in Figures S13 - S16. Due to the O 3 deposition on indoor and human surfaces, the breathing zone O 3 concentration is 40–60% lower than the outdoor concentration (40 ppb) when the far-UVC system is not in operation (see Figure S17), which was also observed in a previous study [ 42 ]. The calculated O 3 generation rate of all far-UVC types, based on the well-mixed mass balance model [ 43 ], is 7.0 (± 1.5) ppb∙h − 1 ∙(µW∙cm − 2 ) −1 , which is consistent with findings from previous studies [ 15 – 17 ]. During one hour of the far-UVC system operation, the breathing zone O 3 concentration increases by 4–6 ppb, and its impact is more significant when the ventilation is relatively low (see Figure S17). For instance, at a ventilation rate of 0.7 h − 1 , far-UVC operation increases O 3 concentration by 40–60%. As the ventilation rate increases to 2 h − 1 and 4 h − 1 , indoor O3 concentration without the far-UVC system is 20–25 ppb due to increased ventilation bringing more outdoor O3 indoors. Consequently, the impact of the far-UVC system operation on indoor O 3 concentration becomes less noticeable. Unlike airborne pathogens, all occupants are exposed to a similar level of O 3 for all far-UVC types (see Figs. 2 e, f, g, and h). However, it is worth noting that a zone with relatively high O 3 concentration is evident in the vicinity of the far-UVC lamp (> 25 ppb) (Figures S13 – S16). Consequently, positioning the far-UVC lamp near occupants is likely to increase human exposure to O 3 and secondary contaminants [ 19 , 20 ]. The OH concentration exhibits a similar pattern to O 3 , with a relatively elevated concentration observed near the far-UVC lamp, as the primary reaction generating OH is the reaction of O 3 with VOCs (see Table S1 and Figures S18 – S21). As the ventilation rate increases from 0.7 h − 1 to 2 h − 1 , the breathing zone OH concentration rises due to the increased introduction of O 3 indoors. However, at a ventilation rate of 4 h − 1 , the OH concentration decreases about 30%, owing to the enhanced removal facilitated by ventilation. In contrast, reaction products show a well-mixed distribution regardless of the far-UVC lamp's position (see Figure S18 and Figures S22 to S24). Moreover, the ventilation condition is important in reducing human exposure to products; increasing ventilation rate from 0.7 h − 1 to 4 h − 1 decreases the breathing zone product concentrations by 90%. Also, the upward airflow pattern created by the buoyancy-driven convective thermal plume under infiltration results in a product concentration within the breathing zone about 20% lower than a well-mixed airflow [ 3 , 24 ]. Implications Our findings suggest that the ceiling-mounted type far-UVC system is most effective at reducing airborne pathogen concentration in a small occupied office. Moreover, this configuration may be considered safer than stand-alone types that create a high O 3 concentration near the occupants. We extrapolate that this trend likely extends to highly occupied environments for the following reasons: Firstly, the position and number of infectors are random, making it difficult to place far-UVC lamps near the path of airborne pathogens. Secondly, airborne pathogens emitted by infectors tend to move upwards due to occupant thermal plume and remain suspended in the air [ 2 , 3 , 38 ]. Consequently, efficient disinfection can occur when a high UV fluence rate is generated above occupants by the ceiling-mounted type far-UVC lamp. Ventilation also plays an important role in removing airborne pathogens as well as secondary contaminants associated with the far-UVC operation. It is essential to bring more fresh air indoors to mitigate human exposure to harmful air contaminants. However, it should be noted that in regions where outdoor O 3 concentration is high (> 40 ppb), the O 3 treatment is indispensable to mitigate its adverse health impacts. Limitations Some limitations should be noted. Firstly, this study modeled the transport and disinfection of airborne pathogens with a fixed particle size of 1 µm, without considering particle size distribution. Secondly, the chemistry modeling included twelve major chemical reactions without encompassing comprehensive chemical reactions such as O 3 and OH reaction with human skin oil were not considered. Future studies are warranted to evaluate airborne disinfection and indoor chemistry, considering such limitations. Declarations Competing interests The authors declare no competing interests. Author Contribution D.R. was responsible for securing funding for the research project to which this paper contributes, conceived the initial idea, and was responsible for leading the project. S.P. and D.R. conducted the literature search. S.P. conducted the CFD model analysis with support from D.R. All authors discussed the data and engineering implications of the study. S.P. drafted the manuscript, with input from D.R. All authors read and revised drafts and approved the final manuscript. Each section of the manuscript was discussed among all authors. Acknowledgment This research was supported by Non-Profit Organization (Blueprint Biosecurity) and the U.S. National Science Foundation (NSF Grant 1944325). Data Availability The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. References Kowalski, W. Ultraviolet germicidal irradiation handbook: UVGI for air and surface disinfection (Springer science & business media, 2010). Park, S., Mistrick, R., Rim, D. Performance of upper-room ultraviolet germicidal irradiation (UVGI) system in learning environments: Effects of ventilation rate, UV fluence rate, and UV radiating volume. Sustain. Cities Soc . 104048 (2022). https://doi.org/10.1016/j.scs.2022.104048 Park, S., Mistrick, R., Sitzabee, W., Rim, D. Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment. Sci. Total Environ . 165454 (2023). https://doi.org/10.1016/j.scitotenv.2023.165454 Blatchley III, E. R., Brenner, D. J., Claus, H., Cowan, T. E., Linden, K. G., Liu, Y., Sliney, D. H. Far UV-C radiation: An emerging tool for pandemic control. Crit. Rev. Environ. Sci. Technol . 53 (6), 733-753 (2023). https://doi.org/10.1080/10643389.2022.2084315 Pereira, A. R., Braga, D. F., Vassal, M., Gomes, I. B., Simões, M. Ultraviolet C irradiation: A promising approach for the disinfection of public spaces?. Sci. Total Environ . 879 , 163007 (2023). https://doi.org/10.1016/j.scitotenv.2023.16300 Welch, D., Buonanno, M., Grilj, V., Shuryak, I., Crickmore, C., Bigelow, A. W., Brenner, D. J. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci. Rep , 8 (1), 2752 (2018). https://doi.org/10.1038/s41598-018-21058-w Buonanno, M., Welch, D., Shuryak, I., & Brenner, D. J. Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. Sci. Rep . 10 (1), 1-8 (2020). https://doi.org/10.1038/s41598-020-67211-2 Eadie, E., Hiwar, W., Fletcher, L., Tidswell, E., O’Mahoney, P., Buonanno, M., Wood, K. Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber. Sci. Rep. 12 (1), 4373 (2022). Kreitenberg, A. and Martinello, R.A. Perspectives and recommendations regarding standards for ultraviolet-C whole-room disinfection in healthcare. J. Res. Natl. Inst. Stand. Technol . 126 (2021). https://doi.org/10.6028/jres.126.015 Zhang, H., & Lai, A. C. Evaluation of single-pass disinfection performance of Far-UVC light on airborne microorganisms in duct flows. Environ. Sci. Technol . 56 (24), 17849-17857 (2022). https://doi.org/10.1021/acs.est.2c04861 Wang, M. H., Zhang, H. H., Chan, C. K., Lee, P. K. H., & Lai, A. C. K. Experimental study of the disinfection performance of a 222-nm Far-UVC upper-room system on airborne microorganisms in a full-scale chamber. Build. Environ . 236 , 110260 (2023). https://doi.org/10.1016/j.buildenv.2023.110260 Narita, K., Asano, K., Morimoto, Y., Igarashi, T., Nakane, A. Chronic irradiation with 222-nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses. PloS one . 13 (7), e0201259 (2018). https://doi.org/10.1371/journal.pone.0201259 Ma, B., Gundy, P. M., Gerba, C. P., Sobsey, M. D., Linden, K. G. UV inactivation of SARS-CoV-2 across the UVC spectrum: KrCl* excimer, mercury-vapor, and light-emitting-diode (LED) sources. Appl. Environ. Microbiol . 87 (22), e01532-21 (2021). https://doi.org/10.1128/AEM.01532-21 Peng, Z., Miller, S. L., Jimenez, J. L. Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps. Environ. Sci. Technol. Lett . 10 (1), 6-13 (2022). https://doi.org/10.1021/acs.estlett.2c00599 Barber, V. P., Goss, M. B., Franco Deloya, L. J., LeMar, L. N., Li, Y., Helstrom, E.; Kroll, J. H. Indoor Air Quality Implications of Germicidal 222 nm Light. Environ. Sci. Technol . 57 (42), 15990-15998 (2023). https://doi.org/10.1021/acs.est.3c05680 Link, M. F., Shore, A., Hamadani, B. H., Poppendieck, D. Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm. Environ. Sci. Technol. Lett . 10 (8), 675-679 (2023). https://doi.org/10.1021/acs.estlett.3c00318 Peng, Z., Day, D. A., Symonds, G. A., Jenks, O. J., Stark, H., Handschy, A. V.; Jimenez, J. L. Significant Production of Ozone from Germicidal UV Lights at 222 nm. Environ. Sci. Technol. Lett . 10 (8), 668-674 (2023). https://doi.org/10.1021/acs.estlett.3c00314 Kalliomäki, P. J., Sobhani, H., Stratton, P., Coleman, K. K., Srikakulapu, A. K., Salawitch, R. J., ... Milton, D. K. Ozone and ultra-fine particle concentrations in a hotel quarantine facility during 222 nm far-UVC air disinfection. medRxiv , 2023-09 (2023). https://doi.org/10.1101/2023.09.29.23296366 Zannoni, N., Lakey, P. S., Won, Y., Shiraiwa, M., Rim, D., Weschler, C. J.; Williams, J. The human oxidation field. Science . 377 (6610), 1071-1077 (2022). https://doi.org/10.1126/science.abn0340 Won, Y., Lakey, P. S., Morrison, G., Shiraiwa, M., Rim, D. Spatial distributions of ozonolysis products from human surfaces in ventilated rooms. Indoor air . 30 (6), 1229-1240 (2020). https://doi.org/10.1111/ina.12700 Collins, D. B., Farmer, D. K. Unintended consequences of air cleaning chemistry. Environ. Sci. Technol . 55 (18), 12172-12179 (2021). https://doi.org/10.1021/acs.est.1c02582 Sung, M., Kato, S. Method to evaluate UV dose of upper-room UVGI system using the concept of ventilation efficiency. Build. Environ . 45 (7), 1626-1631 (2010). https://doi.org/10.1016/j.buildenv.2010.01.011 Gilkeson, C. A., Noakes, C. Application of cfd simulation to predicting upper‐room uvgi effectiveness. Photochem. Photobiol . 89 (4), 799-810 (2013). https://doi.org/10.1111/php.12013 https://plm.sw.siemens.com/en-US/simcenter/fluids-thermal-simulation/star-ccm/ Liu, S., Koupriyanov, M., Paskaruk, D., Fediuk, G., Chen, Q. Investigation of airborne particle exposure in an office with mixing and displacement ventilation. Sustain. Cities Soc . 79 , 103718 (2022). https://doi.org/10.1016/j.scs.2022.103718 Chao, C. Y. H., Wan, M. P., Morawska, L., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Katoshevski, D. Characterization of expiration air jets and droplet size distributions immediately at the mouth opening. J. Aerosol Sci . 40 (2), 122-133 (2009). https://doi.org/10.1016/j.jaerosci.2008.10.003 Ai, Z. T., Melikov, A. K. Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review. Indoor Air . 28 (4), 500-524 (2018). https://doi.org/10.1111/ina.12465 Pei, G., Taylor, M., Rim, D. Human exposure to respiratory aerosols in a ventilated room: Effects of ventilation condition, emission mode, and social distancing. Sustain. Cities Soc . 73 , 103090 (2021). https://doi.org/10.1016/j.scs.2021.103090 Morawska, L. J. G. R., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Mengersen, K., Corbett, S., Katoshevski, D. (2009). Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. J. Aerosol Sci . 40 (3), 256-269 (2009). https://doi.org/10.1016/j.jaerosci.2008.11.002 Lai, A. C., Nazaroff, W. W. Modeling indoor particle deposition from turbulent flow onto smooth surfaces. J. Aerosol Sci . 31 (4), 463-476 (2000). https://doi.org/10.1016/S0021-8502(99)00536-4 ASHRAE. Fundamentals, chapter 18: Nonresidential cooling and heating load calculations ( ASHRAE , Atlanta. GA, USA, 2021). Niu, Y., Cai, J., Xia, Y., Yu, H., Chen, R., Lin, Z.; Kan, H. Estimation of personal ozone exposure using ambient concentrations and influencing factors. Environ. Int . 117 , 237-242 (2018). https://doi.org/10.1016/j.envint.2018.05.017 Lee, K., Vallarino, J., Dumyahn, T., Ozkaynak, H., Spengler, J. D. Ozone decay rates in residences. J. Air Waste Manag. Assoc . 49 (10), 1238-1244 (1999). https://doi.org/10.1080/10473289.1999.10463913 Holøs, S. B., Yang, A., Lind, M., Thunshelle, K., Schild, P., Mysen, M. VOC emission rates in newly built and renovated buildings, and the influence of ventilation–a review and meta-analysis. Int J. Vent . 18 (3), 153-166 (2019). https://doi.org/10.1080/14733315.2018.1435026 Wang, N., Ernle, L., Beko, G., Wargocki, P., Williams, J. Emission rates of volatile organic compounds from humans. Environ. Sci. Technol . 56 (8), 4838-4848 (2022). https://doi.org/10.1021/acs.est.1c08764 https://www.acuitybrands.com/resources/technical-resources/visual-lighting-software ANSI/ASHRAE. Standard 62.1-2019: Ventilation for acceptable indoor air quality ( ASHRAE , Atlanta. GA, USA , 2019). The Lancet COVID-19 commission, Proposed non-infectious air deliver rates (NADR) for reducing exposure to airborne respiratory infectious diseases . 2022. https://covid19commission.org/safe-work-travel Rim, D., Novoselec, A., & Morrison, G. The influence of chemical interactions at the human surface on breathing zone levels of reactants and products. Indoor Air . 19 (4), 324-334 (2009). https://doi.org/10.1111/j.1600-0668.2009.00595.x Nicas, M., Nazaroff, W. W., Hubbard, A. Toward understanding the risk of secondary airborne infection: emission of respirable pathogens. J. Occup. Environ. Hyg . 2 (3), 143-154 (2005). https://doi.org/10.1080/15459620590918466 Lin, Z., Wang, J., Yao, T., Chow, T. T. Investigation into anti-airborne infection performance of stratum ventilation. Build. Environ . 54 , 29-38 (2012). https://doi.org/10.1016/j.buildenv.2012.01.017 Nazaroff, W. W., Weschler, C. J. Indoor ozone: Concentrations and influencing factors. Indoor air . 32 (1), e12942 (2022). https://doi.org/10.1111/ina.12942 Park, S., Lee, S., Yeo, M. S., Rim, D. Performance of a heat recovery ventilation system for controlling human exposure to airborne particles in a residential building. Build. Environ . 239 , 110412 (2023). https://doi.org/10.1016/j.buildenv.2023.110412 Additional Declarations No competing interests reported. Supplementary Files 240516Supportinginformation.pdf Cite Share Download PDF Status: Published Journal Publication published 18 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 16 Jul, 2024 Reviews received at journal 29 Jun, 2024 Reviews received at journal 07 Jun, 2024 Reviewers agreed at journal 03 Jun, 2024 Reviewers agreed at journal 03 Jun, 2024 Reviewers invited by journal 01 Jun, 2024 Editor assigned by journal 01 Jun, 2024 Editor invited by journal 23 May, 2024 Submission checks completed at journal 23 May, 2024 First submitted to journal 14 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4421781","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":310147633,"identity":"454994bc-3395-4e8e-94ba-933a04b06f9c","order_by":0,"name":"Seongjun Park","email":"","orcid":"","institution":"Pennsylvania State University","correspondingAuthor":false,"prefix":"","firstName":"Seongjun","middleName":"","lastName":"Park","suffix":""},{"id":310147634,"identity":"0ff7c41c-5abc-42b5-b442-1a18b176ef65","order_by":1,"name":"Donghyun Rim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsElEQVRIiWNgGAWjYDCCAwzsHxIqIGwJYrWwMTw4Q6oWxodtpGjhu5H77EHivDv2BgeYD97mIUaL5Jnj5gaJ254lbjjAlmxNlBaD420MEonbDicYHOAxkyZOy2E2oJY5h4EO4/9GpJbjbWwSiQ2HGTcc4GEjTovkmWPMBgnHniXOPMxmbDmHGC18N9IYH/6ouWPPd7z54Y03xGiBggMMDMwkKIdqGQWjYBSMglGACwAAjEk2BuXnGokAAAAASUVORK5CYII=","orcid":"","institution":"Pennsylvania State University","correspondingAuthor":true,"prefix":"","firstName":"Donghyun","middleName":"","lastName":"Rim","suffix":""}],"badges":[],"createdAt":"2024-05-15 01:02:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4421781/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4421781/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-75245-z","type":"published","date":"2024-10-18T15:57:35+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57793173,"identity":"c48709c5-fc2f-44a2-a34c-fdec7c64959e","added_by":"auto","created_at":"2024-06-05 18:10:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":196839,"visible":true,"origin":"","legend":"\u003cp\u003ePositions of far-UVC lamp. Note that the lamp power was set to meet the room average UV fluence rate of 3 μW∙cm\u003csup\u003e-2\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4421781/v1/f4a3eb6d98319adddddb4830.png"},{"id":57793177,"identity":"b3c58a39-9342-4fe4-8ab8-0ff6cadc83ec","added_by":"auto","created_at":"2024-06-05 18:10:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":354556,"visible":true,"origin":"","legend":"\u003cp\u003eAirborne pathogens intake fraction (a, b, c, and d) and 1-hr exposure to O\u003csub\u003e3\u003c/sub\u003e (e, f, g, and h). Note that BZ is the ASHRAE breathing zone average concentration (defined as the air volume ranging from 8 cm to 180 cm above 60 cm away from walls) [35], and P1 - 4 are the breathing box concentration of each occupant (defined as a 500 cm\u003csup\u003e3\u003c/sup\u003e air volume below the nose tip) [37]. The error bars represent the standard deviation of intake fraction within the ASHRAE breathing zone.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4421781/v1/20745fcac1b28578558b3a26.png"},{"id":67149793,"identity":"3f747a6f-619c-4999-aee3-4e2726820a41","added_by":"auto","created_at":"2024-10-21 16:14:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":977311,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4421781/v1/2bb3b79f-9c7b-4286-92f7-24b411645c8a.pdf"},{"id":57793175,"identity":"b17a64fd-43ff-4c34-aa94-3232b0a8ca3d","added_by":"auto","created_at":"2024-06-05 18:10:14","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4005750,"visible":true,"origin":"","legend":"","description":"","filename":"240516Supportinginformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4421781/v1/2dfbf605510c1e2cd745fad0.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Human exposure to air contaminants under the far-UVC system operation in an office: Effects of lamp position and ventilation condition","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn the wake of the novel coronavirus (COVID-19) outbreak, the germicidal ultraviolet (GUV) system has emerged as a prominent solution for effectively controlling airborne pathogens. Traditionally, ultraviolet C (UVC) at 254 nm has been used to irradiate the upper section of rooms, primarily due to its known adverse effects on human skin cells. [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In recent times, there has been a growing preference for utilizing shorter wavelengths, known as far-UVC, which involves KrCl excimer lamps emitting UVC at a peak wavelength of 222 nm [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Far-UVC has demonstrated the capability to deactivate airborne pathogens by degrading their genetic material and impeding their reproductive capacity [\u003cspan additionalcitationids=\"CR7 CR8 CR9 CR10\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Notably, its minimal impact on human tissues positions it as a viable method for comprehensive indoor disinfection [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, concerns have been raised regarding the potential of the far-UVC system to serve as an indoor O\u003csub\u003e3\u003c/sub\u003e source [\u003cspan additionalcitationids=\"CR15 CR16 CR17\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The photolysis of O\u003csub\u003e2\u003c/sub\u003e by the wavelength range of 175\u0026ndash;242 nm, inherent to this system, results in O\u003csub\u003e3\u003c/sub\u003e generation. While O\u003csub\u003e3\u003c/sub\u003e itself poses risks, it also instigates indoor chemical reactions, leading to the formation of air pollutants such as oxidants and secondary organic aerosols (SOA) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan additionalcitationids=\"CR19 CR20\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe market offers various configurations of far-UVC lamps, including ceiling-mounted, wall-mounted, and stand-alone types. Given a high UV intensity near the lamp that rapidly decreases with distance, the positioning of the far-UVC lamp significantly affects the distribution of UV intensity within a space [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. This distribution can not only impact the removal efficiency of pathogens but also influence the rate constant of O\u003csub\u003e2\u003c/sub\u003e photolysis by UVC at 222 nm [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Therefore, the placement of the far-UVC system is intricately linked to human exposure to airborne pathogens and secondary contaminants.\u003c/p\u003e \u003cp\u003eIn this study, we investigate detailed airborne pathogen disinfection and indoor O\u003csub\u003e3\u003c/sub\u003e chemistry due to far-UVC system within an office environment, based on a computational fluid dynamics (CFD) simulation. By examining impacts of six different positions of the far-UVC lamp under four ventilation conditions, our investigation elucidates the implications of far-UVC lamps for human exposure to airborne pathogens and secondary contaminants.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eWe conducted simulations to analyze the disinfection of airborne pathogens and secondary contaminant formation associated with the far-UVC system operation. These simulations were carried out using the commercial CFD solver STAR-CCM+ (version 2021.03) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In the CFD model, airborne pathogen and chemical reactions were modeled simultaneously. The Eulerian model was employed to simulate airborne pathogens, whereas the multi-component gas model was utilized for modeling chemical reactions.\u003c/p\u003e \u003cp\u003eWe created the simulation domain with dimensions of 7.0 m \u0026times; 5.8 m \u0026times; 3.1 m (length \u0026times; width \u0026times; height) and included four occupants (see Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) based on the experimental setup outlined by Liu et al. (2022) [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Given that the highest airborne pathogen concentration occurred when the occupant 4 (P4) was infected and speaking (see Figure S7), we designated P4 as a constant source of airborne pathogens. Specifically, P4 continuously emitted airborne pathogens from a 1.2 cm\u003csup\u003e2\u003c/sup\u003e mouth opening with an air speed of 4 m∙s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a horizontal direction [\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The size of airborne pathogens emitted from the infector\u0026rsquo;s mouth was set to 1 \u0026micro;m with a density of 1000 kg∙m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, based on the dominant droplet size for the talking mode [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The emission concentration was maintained at 1 \u0026micro;g∙m\u003csup\u003e3\u003c/sup\u003e. Airborne pathogens were then removed by ventilation and deposition onto the floor with a deposition velocity of 0.003 cm∙s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The susceptibility constant of airborne pathogens to UVC at 222 nm was set to 1.4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e∙\u0026micro;W\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e∙s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, simulating SARS-CoV-2 [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Each occupant generates a metabolic heat of 99W in seating mode [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eChemical reactions associated with far-UVC system were modeled based on Barber et al. (2023) [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], incorporating a total of 12 chemical reactions in the CFD simulation (see Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). In the chemistry simulation, we assumed that there was no indoor O\u003csub\u003e3\u003c/sub\u003e source and no UV radiation through windows. The outdoor O\u003csub\u003e3\u003c/sub\u003e concentration was set to 40 ppb, considering typical urban environments [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Indoor O\u003csub\u003e3\u003c/sub\u003e was removed from room surfaces at a deposition rate of 2.8 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] and from human surfaces at a deposition velocity of 6.8 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Assuming a typical indoor condition, the VOCs emission rates from indoor surfaces and occupants were set at 150 \u0026micro;g∙m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e∙h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1 \u0026micro;g∙s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e∙person\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Note that all chemical reactions occur under atmospheric conditions of 1 atm pressure, a relative humidity ranging from 35\u0026ndash;40%, and a temperature of 298 K, which are typical indoor conditions at sea level. Further details regarding boundary conditions and the CFD simulation setup can be found in Sections S1 and S2 of the Supporting Information.\u003c/p\u003e \u003cp\u003eTo investigate the effect of the far-UVC lamp position relative to the occupant area, we modeled six different positions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): ceiling-mounted type, wall-mounted type, and stand-alone type 1\u0026ndash;4. The ceiling-mounted far-UVC lamp emits a 120-degree beam, while other types produce a beam in all directions. The power of each lamp was adjusted to achieve the room average UV fluence rate of 3 \u0026micro;W∙cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and the spatial distributions of UV fluence rates were obtained using the Visual Software [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The average UV fluence rate within the human envelope zone of all lamp types remains below 1.1 \u0026micro;W∙cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, meeting the eye exposure limit standards set by the American Conference of Governmental Industrial Hygienists (ACGIH) eye limit (0.3\u0026ndash;1.5 \u0026micro;W∙cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Note that the human envelope zone is defined as a 0.8 m\u003csup\u003e3\u003c/sup\u003e box air volume near the human body (see Figure S8) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlong with six lamp positions, four distinct ventilation conditions were examined: mixing ventilation at rates of 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 2 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and infiltration at a rate of 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Note that the 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is the minimum requirements by ASHRAE [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], and 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is considered good by The Lancet COVID-19 commission [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo enhance the credibility of our CFD model, we conducted validation exercises to assess its ability to predict airborne transmission and indoor chemical reactions. Specifically, we validated the airflow field and particle transport within a room, the time-series airborne pathogen concentrations, O\u003csub\u003e3\u003c/sub\u003e generation by indoor chemical reactions, and O\u003csub\u003e3\u003c/sub\u003e deposition were validated by comparing the CFD result with the experimental data and well-mixed mass balance model. Further details on the CFD model validation can be found in Section S3.\u003c/p\u003e \u003cp\u003eTo analyze the infection risk related to the inhalation of airborne pathogens, we used a metric \u0026ldquo;intake faction\u0026rdquo; within the ASHRAE breathing zone and the human breathing box for one hour (Eq.\u0026nbsp;1) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Note that the ASHRAE breathing zone is defined as the air volume extending from 8 cm to 180 cm above 60 cm away from walls [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], and the human breathing box is defined as a 500 cm\u003csup\u003e3\u003c/sup\u003e air volume below the nose tip) [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(Intake fraction= \\frac{{\\int }_{0}^{T}{Q}_{b}C\\left(t\\right)dt}{{\\int }_{0}^{T}E\\left(t\\right)dt}\\)\u003c/span\u003e \u003c/span\u003e Eq.\u0026nbsp;1\u003c/p\u003e \u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{b}\\)\u003c/span\u003e\u003c/span\u003e is the breathing flow rate of occupants (rest mode \u0026minus;\u0026thinsp;0.6 m\u003csup\u003e3\u003c/sup\u003e∙h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(C\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is the contaminant concentration, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(E\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is the emission rate, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(T\\)\u003c/span\u003e\u003c/span\u003e is the total emission time.\u003c/p\u003e \u003cp\u003eSimilarly, we presented the results of O\u003csub\u003e3\u003c/sub\u003e, OH, and products as a one-hour integrated exposure within the ASHRAE breathing zone and the human breathing box (Eq.\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(Exposure= {\\int }_{0}^{T}tC\\left(t\\right)dt\\)\u003c/span\u003e \u003c/span\u003e Eq.\u0026nbsp;2\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eAirborne pathogen transmission\u003c/h2\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b, c, and d illustrate the intake fraction within the ASHRAE breathing zone over one hour under four different ventilation conditions. Details of the airborne pathogen distributions at one hour are provided in Figures S9 and S10.\u003c/p\u003e \u003cp\u003eFar-UVC systems demonstrate a reduction in airborne pathogen concentration by 50\u0026ndash;85% after one hour (see Figure S11), resulting in 40\u0026ndash;80% decreases in 1-h human exposure. Notably, while stand-alone types exhibit a higher UV fluence rate within the breathing zone, the ceiling-mounted type shows a more pronounced reduction effect across all types. Specifically, at a ventilation rate of 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the ceiling-mounted type lowers the intake fraction from 2.12 to 0.46 under mixing ventilation and from 2.24 to 0.63 under the infiltration condition. This is mainly because airborne pathogens emitted from an infector tend to ascend with the room airflow, reaching the upper region close to a far-UVC lamp on the ceiling (Figure S12). Meanwhile, the wall-mounted type yields a 60\u0026ndash;70% higher intake fraction than the ceiling-mounted type. The notable difference is attributed to the ceiling-mounted type creating a higher UV fluence rate than the wall-mounted type within both the breathing zone and upper region of the room, where airborne pathogens accumulate under the effects of occupant thermal plumes.\u003c/p\u003e \u003cp\u003eThe reduction effect of stand-alone types is less than that of the ceiling-mounted type and varies with position and ventilation conditions. For example, type 1 (closest to the infector) consistently shows the highest reduction under mixing ventilation, while, under infiltration, types 3 (3 m away from the infector) yield the lowest intake fraction.\u003c/p\u003e \u003cp\u003eIn addition to the positioning of far-UVC systems, ventilation conditions play a crucial role in determining human exposure to airborne pathogens. Increased ventilation not only dilutes airborne pathogens but also influences personal exposure, as reflected by the intake fraction within the breathing box. When the ventilation rate is 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under mixing ventilation, P1 (facing the infector, P4) is exposed to airborne pathogens more than two times higher than P2 and P3 (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Under infiltration, the intake fraction within the breathing box for P1 exceeds those of P2 and P3 by up to ninefold (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). This is primarily due to the reduced air mixing effect under infiltration, allowing the air jet emitted from the infector's mouth to travel a longer distance toward the occupant positioned directly in front of the infector [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. On the other hand, at ventilation rates of 2 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the increased air mixing effect results in relatively uniform exposure to airborne pathogens among all occupants (see Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and c). This finding suggests that higher ventilation rates can help reduce human exposure to airborne pathogens and also ensure equal protection for all occupants.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eExposure to secondary contaminants\u003c/h2\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, f, g, and h illustrate 1-h human exposure to O\u003csub\u003e3\u003c/sub\u003e within the ASHRAE breathing zone under four different ventilation conditions. Detailed O\u003csub\u003e3\u003c/sub\u003e concentration contours at one hour for all conditions are provided in Figures S13 - S16.\u003c/p\u003e \u003cp\u003eDue to the O\u003csub\u003e3\u003c/sub\u003e deposition on indoor and human surfaces, the breathing zone O\u003csub\u003e3\u003c/sub\u003e concentration is 40\u0026ndash;60% lower than the outdoor concentration (40 ppb) when the far-UVC system is not in operation (see Figure S17), which was also observed in a previous study [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. The calculated O\u003csub\u003e3\u003c/sub\u003e generation rate of all far-UVC types, based on the well-mixed mass balance model [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], is 7.0 (\u0026plusmn;\u0026thinsp;1.5) ppb∙h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e∙(\u0026micro;W∙cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003csup\u003e\u0026minus;1\u003c/sup\u003e, which is consistent with findings from previous studies [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDuring one hour of the far-UVC system operation, the breathing zone O\u003csub\u003e3\u003c/sub\u003e concentration increases by 4\u0026ndash;6 ppb, and its impact is more significant when the ventilation is relatively low (see Figure S17). For instance, at a ventilation rate of 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, far-UVC operation increases O\u003csub\u003e3\u003c/sub\u003e concentration by 40\u0026ndash;60%. As the ventilation rate increases to 2 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indoor O3 concentration without the far-UVC system is 20\u0026ndash;25 ppb due to increased ventilation bringing more outdoor O3 indoors. Consequently, the impact of the far-UVC system operation on indoor O\u003csub\u003e3\u003c/sub\u003e concentration becomes less noticeable.\u003c/p\u003e \u003cp\u003eUnlike airborne pathogens, all occupants are exposed to a similar level of O\u003csub\u003e3\u003c/sub\u003e for all far-UVC types (see Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, f, g, and h). However, it is worth noting that a zone with relatively high O\u003csub\u003e3\u003c/sub\u003e concentration is evident in the vicinity of the far-UVC lamp (\u0026gt;\u0026thinsp;25 ppb) (Figures S13 \u0026ndash; S16). Consequently, positioning the far-UVC lamp near occupants is likely to increase human exposure to O\u003csub\u003e3\u003c/sub\u003e and secondary contaminants [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe OH concentration exhibits a similar pattern to O\u003csub\u003e3\u003c/sub\u003e, with a relatively elevated concentration observed near the far-UVC lamp, as the primary reaction generating OH is the reaction of O\u003csub\u003e3\u003c/sub\u003e with VOCs (see Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and Figures S18 \u0026ndash; S21). As the ventilation rate increases from 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 2 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the breathing zone OH concentration rises due to the increased introduction of O\u003csub\u003e3\u003c/sub\u003e indoors. However, at a ventilation rate of 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the OH concentration decreases about 30%, owing to the enhanced removal facilitated by ventilation.\u003c/p\u003e \u003cp\u003eIn contrast, reaction products show a well-mixed distribution regardless of the far-UVC lamp's position (see Figure S18 and Figures S22 to S24). Moreover, the ventilation condition is important in reducing human exposure to products; increasing ventilation rate from 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e decreases the breathing zone product concentrations by 90%. Also, the upward airflow pattern created by the buoyancy-driven convective thermal plume under infiltration results in a product concentration within the breathing zone about 20% lower than a well-mixed airflow [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eImplications\u003c/h3\u003e\n\u003cp\u003eOur findings suggest that the ceiling-mounted type far-UVC system is most effective at reducing airborne pathogen concentration in a small occupied office. Moreover, this configuration may be considered safer than stand-alone types that create a high O\u003csub\u003e3\u003c/sub\u003e concentration near the occupants. We extrapolate that this trend likely extends to highly occupied environments for the following reasons: Firstly, the position and number of infectors are random, making it difficult to place far-UVC lamps near the path of airborne pathogens. Secondly, airborne pathogens emitted by infectors tend to move upwards due to occupant thermal plume and remain suspended in the air [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Consequently, efficient disinfection can occur when a high UV fluence rate is generated above occupants by the ceiling-mounted type far-UVC lamp.\u003c/p\u003e \u003cp\u003eVentilation also plays an important role in removing airborne pathogens as well as secondary contaminants associated with the far-UVC operation. It is essential to bring more fresh air indoors to mitigate human exposure to harmful air contaminants. However, it should be noted that in regions where outdoor O\u003csub\u003e3\u003c/sub\u003e concentration is high (\u0026gt;\u0026thinsp;40 ppb), the O\u003csub\u003e3\u003c/sub\u003e treatment is indispensable to mitigate its adverse health impacts.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eSome limitations should be noted. Firstly, this study modeled the transport and disinfection of airborne pathogens with a fixed particle size of 1 \u0026micro;m, without considering particle size distribution. Secondly, the chemistry modeling included twelve major chemical reactions without encompassing comprehensive chemical reactions such as O\u003csub\u003e3\u003c/sub\u003e and OH reaction with human skin oil were not considered. Future studies are warranted to evaluate airborne disinfection and indoor chemistry, considering such limitations.\u003c/p\u003e \u003c/div\u003e "},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eD.R. was responsible for securing funding for the research project to which this paper contributes, conceived the initial idea, and was responsible for leading the project. S.P. and D.R. conducted the literature search. S.P. conducted the CFD model analysis with support from D.R. All authors discussed the data and engineering implications of the study. S.P. drafted the manuscript, with input from D.R. All authors read and revised drafts and approved the final manuscript. Each section of the manuscript was discussed among all authors.\u003c/p\u003e\u003ch2\u003eAcknowledgment\u003c/h2\u003e \u003cp\u003eThis research was supported by Non-Profit Organization (Blueprint Biosecurity) and the U.S. National Science Foundation (NSF Grant 1944325).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKowalski, W. Ultraviolet germicidal irradiation handbook: UVGI for air and surface disinfection (Springer science \u0026amp; business media, 2010).\u003c/li\u003e\n\u003cli\u003ePark, S., Mistrick, R., Rim, D. Performance of upper-room ultraviolet germicidal irradiation (UVGI) system in learning environments: Effects of ventilation rate, UV fluence rate, and UV radiating volume. \u003cem\u003eSustain. Cities Soc\u003c/em\u003e. \u003cstrong\u003e104048 \u003c/strong\u003e(2022). https://doi.org/10.1016/j.scs.2022.104048\u003c/li\u003e\n\u003cli\u003ePark, S., Mistrick, R., Sitzabee, W., Rim, D. Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment. \u003cem\u003eSci. Total Environ\u003c/em\u003e. \u003cstrong\u003e165454\u003c/strong\u003e (2023). https://doi.org/10.1016/j.scitotenv.2023.165454\u003c/li\u003e\n\u003cli\u003eBlatchley III, E. R., Brenner, D. J., Claus, H., Cowan, T. E., Linden, K. G., Liu, Y., Sliney, D. H. Far UV-C radiation: An emerging tool for pandemic control. \u003cem\u003eCrit. Rev. Environ. Sci. Technol\u003c/em\u003e. \u003cstrong\u003e53\u003c/strong\u003e (6), 733-753 (2023). https://doi.org/10.1080/10643389.2022.2084315\u003c/li\u003e\n\u003cli\u003ePereira, A. R., Braga, D. F., Vassal, M., Gomes, I. B., Sim\u0026otilde;es, M. Ultraviolet C irradiation: A promising approach for the disinfection of public spaces?. \u003cem\u003eSci. Total Environ\u003c/em\u003e. \u003cstrong\u003e879\u003c/strong\u003e, 163007 (2023). https://doi.org/10.1016/j.scitotenv.2023.16300\u003c/li\u003e\n\u003cli\u003eWelch, D., Buonanno, M., Grilj, V., Shuryak, I., Crickmore, C., Bigelow, A. W., Brenner, D. J. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. \u003cem\u003eSci. Rep\u003c/em\u003e, \u003cstrong\u003e8\u003c/strong\u003e (1), 2752 (2018). https://doi.org/10.1038/s41598-018-21058-w\u003c/li\u003e\n\u003cli\u003eBuonanno, M., Welch, D., Shuryak, I., \u0026amp; Brenner, D. J. Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. \u003cem\u003eSci. Rep\u003c/em\u003e. \u003cstrong\u003e10\u003c/strong\u003e (1), 1-8 (2020). https://doi.org/10.1038/s41598-020-67211-2\u003c/li\u003e\n\u003cli\u003eEadie, E., Hiwar, W., Fletcher, L., Tidswell, E., O\u0026rsquo;Mahoney, P., Buonanno, M., Wood, K. Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber. \u003cem\u003eSci. Rep.\u003c/em\u003e\u003cstrong\u003e12\u003c/strong\u003e (1), 4373 (2022).\u003c/li\u003e\n\u003cli\u003eKreitenberg, A. and Martinello, R.A. Perspectives and recommendations regarding standards for ultraviolet-C whole-room disinfection in healthcare. \u003cem\u003eJ. Res. Natl. Inst. Stand. Technol\u003c/em\u003e. \u003cstrong\u003e126\u003c/strong\u003e (2021). https://doi.org/10.6028/jres.126.015\u003c/li\u003e\n\u003cli\u003eZhang, H., \u0026amp; Lai, A. C. Evaluation of single-pass disinfection performance of Far-UVC light on airborne microorganisms in duct flows. \u003cem\u003eEnviron. Sci. Technol\u003c/em\u003e. \u003cstrong\u003e56\u003c/strong\u003e (24), 17849-17857 (2022). https://doi.org/10.1021/acs.est.2c04861\u003c/li\u003e\n\u003cli\u003eWang, M. H., Zhang, H. H., Chan, C. K., Lee, P. K. H., \u0026amp; Lai, A. C. K. Experimental study of the disinfection performance of a 222-nm Far-UVC upper-room system on airborne microorganisms in a full-scale chamber. \u003cem\u003eBuild. Environ\u003c/em\u003e. \u003cstrong\u003e236\u003c/strong\u003e, 110260 (2023). https://doi.org/10.1016/j.buildenv.2023.110260\u003c/li\u003e\n\u003cli\u003eNarita, K., Asano, K., Morimoto, Y., Igarashi, T., Nakane, A. Chronic irradiation with 222-nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses. \u003cem\u003ePloS one\u003c/em\u003e. \u003cstrong\u003e13\u003c/strong\u003e (7), e0201259 (2018). https://doi.org/10.1371/journal.pone.0201259\u003c/li\u003e\n\u003cli\u003eMa, B., Gundy, P. M., Gerba, C. P., Sobsey, M. D., Linden, K. G. UV inactivation of SARS-CoV-2 across the UVC spectrum: KrCl* excimer, mercury-vapor, and light-emitting-diode (LED) sources. \u003cem\u003eAppl. Environ. Microbiol\u003c/em\u003e. \u003cstrong\u003e87\u003c/strong\u003e (22), e01532-21 (2021). https://doi.org/10.1128/AEM.01532-21\u003c/li\u003e\n\u003cli\u003ePeng, Z., Miller, S. L., Jimenez, J. L. Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps. \u003cem\u003eEnviron. Sci. Technol. Lett\u003c/em\u003e. \u003cstrong\u003e10\u003c/strong\u003e (1), 6-13 (2022). https://doi.org/10.1021/acs.estlett.2c00599\u003c/li\u003e\n\u003cli\u003eBarber, V. P., Goss, M. B., Franco Deloya, L. J., LeMar, L. N., Li, Y., Helstrom, E.; Kroll, J. H. Indoor Air Quality Implications of Germicidal 222 nm Light. \u003cem\u003eEnviron. Sci. Technol\u003c/em\u003e. \u003cstrong\u003e57\u003c/strong\u003e (42), 15990-15998 (2023). https://doi.org/10.1021/acs.est.3c05680\u003c/li\u003e\n\u003cli\u003eLink, M. F., Shore, A., Hamadani, B. H., Poppendieck, D. Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm. \u003cem\u003eEnviron. Sci. Technol. Lett\u003c/em\u003e. \u003cstrong\u003e10\u003c/strong\u003e (8), 675-679 (2023). https://doi.org/10.1021/acs.estlett.3c00318\u003c/li\u003e\n\u003cli\u003ePeng, Z., Day, D. A., Symonds, G. A., Jenks, O. J., Stark, H., Handschy, A. V.; Jimenez, J. L. Significant Production of Ozone from Germicidal UV Lights at 222 nm. \u003cem\u003eEnviron. Sci. Technol. Lett\u003c/em\u003e. \u003cstrong\u003e10\u003c/strong\u003e (8), 668-674 (2023). https://doi.org/10.1021/acs.estlett.3c00314\u003c/li\u003e\n\u003cli\u003eKalliom\u0026auml;ki, P. J., Sobhani, H., Stratton, P., Coleman, K. K., Srikakulapu, A. K., Salawitch, R. J., ... Milton, D. K. Ozone and ultra-fine particle concentrations in a hotel quarantine facility during 222 nm far-UVC air disinfection. \u003cem\u003emedRxiv\u003c/em\u003e, 2023-09 (2023). https://doi.org/10.1101/2023.09.29.23296366\u003c/li\u003e\n\u003cli\u003eZannoni, N., Lakey, P. S., Won, Y., Shiraiwa, M., Rim, D., Weschler, C. J.; Williams, J. The human oxidation field. \u003cem\u003eScience\u003c/em\u003e. \u003cstrong\u003e377\u003c/strong\u003e (6610), 1071-1077 (2022). https://doi.org/10.1126/science.abn0340\u003c/li\u003e\n\u003cli\u003eWon, Y., Lakey, P. S., Morrison, G., Shiraiwa, M., Rim, D. Spatial distributions of ozonolysis products from human surfaces in ventilated rooms. \u003cem\u003eIndoor air\u003c/em\u003e. \u003cstrong\u003e30\u003c/strong\u003e (6), 1229-1240 (2020). https://doi.org/10.1111/ina.12700\u003c/li\u003e\n\u003cli\u003eCollins, D. B., Farmer, D. K. Unintended consequences of air cleaning chemistry. \u003cem\u003eEnviron. Sci. Technol\u003c/em\u003e. \u003cstrong\u003e55\u003c/strong\u003e (18), 12172-12179 (2021). https://doi.org/10.1021/acs.est.1c02582\u003c/li\u003e\n\u003cli\u003eSung, M., Kato, S. Method to evaluate UV dose of upper-room UVGI system using the concept of ventilation efficiency. \u003cem\u003eBuild. Environ\u003c/em\u003e. \u003cstrong\u003e45\u003c/strong\u003e (7), 1626-1631 (2010). https://doi.org/10.1016/j.buildenv.2010.01.011\u003c/li\u003e\n\u003cli\u003eGilkeson, C. A., Noakes, C. Application of cfd simulation to predicting upper‐room uvgi effectiveness. \u003cem\u003ePhotochem. Photobiol\u003c/em\u003e. \u003cstrong\u003e89\u003c/strong\u003e (4), 799-810 (2013). https://doi.org/10.1111/php.12013\u003c/li\u003e\n\u003cli\u003ehttps://plm.sw.siemens.com/en-US/simcenter/fluids-thermal-simulation/star-ccm/\u003c/li\u003e\n\u003cli\u003eLiu, S., Koupriyanov, M., Paskaruk, D., Fediuk, G., Chen, Q. Investigation of airborne particle exposure in an office with mixing and displacement ventilation. \u003cem\u003eSustain. Cities Soc\u003c/em\u003e. \u003cstrong\u003e79\u003c/strong\u003e, 103718 (2022). https://doi.org/10.1016/j.scs.2022.103718\u003c/li\u003e\n\u003cli\u003eChao, C. Y. H., Wan, M. P., Morawska, L., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Katoshevski, D. Characterization of expiration air jets and droplet size distributions immediately at the mouth opening. \u003cem\u003eJ. Aerosol Sci\u003c/em\u003e. \u003cstrong\u003e40\u003c/strong\u003e (2), 122-133 (2009). https://doi.org/10.1016/j.jaerosci.2008.10.003\u003c/li\u003e\n\u003cli\u003eAi, Z. T., Melikov, A. K. Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review. \u003cem\u003eIndoor Air\u003c/em\u003e. \u003cstrong\u003e28\u003c/strong\u003e (4), 500-524 (2018). https://doi.org/10.1111/ina.12465\u003c/li\u003e\n\u003cli\u003ePei, G., Taylor, M., Rim, D. Human exposure to respiratory aerosols in a ventilated room: Effects of ventilation condition, emission mode, and social distancing. \u003cem\u003eSustain. Cities Soc\u003c/em\u003e. \u003cstrong\u003e73\u003c/strong\u003e, 103090 (2021). https://doi.org/10.1016/j.scs.2021.103090\u003c/li\u003e\n\u003cli\u003eMorawska, L. J. G. R., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Mengersen, K., Corbett, S., Katoshevski, D. (2009). Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. \u003cem\u003eJ. Aerosol Sci\u003c/em\u003e. \u003cstrong\u003e40\u003c/strong\u003e (3), 256-269 (2009). https://doi.org/10.1016/j.jaerosci.2008.11.002\u003c/li\u003e\n\u003cli\u003eLai, A. C., Nazaroff, W. W. Modeling indoor particle deposition from turbulent flow onto smooth surfaces. \u003cem\u003eJ. Aerosol Sci\u003c/em\u003e. \u003cstrong\u003e31\u003c/strong\u003e (4), 463-476 (2000). https://doi.org/10.1016/S0021-8502(99)00536-4\u003c/li\u003e\n\u003cli\u003eASHRAE. Fundamentals, chapter 18: Nonresidential cooling and heating load calculations (\u003cem\u003eASHRAE\u003c/em\u003e, Atlanta. GA, USA, 2021).\u003c/li\u003e\n\u003cli\u003eNiu, Y., Cai, J., Xia, Y., Yu, H., Chen, R., Lin, Z.; Kan, H. Estimation of personal ozone exposure using ambient concentrations and influencing factors. \u003cem\u003eEnviron. Int\u003c/em\u003e. \u003cstrong\u003e117\u003c/strong\u003e, 237-242 (2018). https://doi.org/10.1016/j.envint.2018.05.017\u003c/li\u003e\n\u003cli\u003eLee, K., Vallarino, J., Dumyahn, T., Ozkaynak, H., Spengler, J. D. Ozone decay rates in residences. \u003cem\u003eJ. Air Waste Manag. Assoc\u003c/em\u003e. \u003cstrong\u003e49\u003c/strong\u003e (10), 1238-1244 (1999). https://doi.org/10.1080/10473289.1999.10463913\u003c/li\u003e\n\u003cli\u003eHol\u0026oslash;s, S. B., Yang, A., Lind, M., Thunshelle, K., Schild, P., Mysen, M. VOC emission rates in newly built and renovated buildings, and the influence of ventilation\u0026ndash;a review and meta-analysis. \u003cem\u003eInt J. Vent\u003c/em\u003e. \u003cstrong\u003e18\u003c/strong\u003e (3), 153-166 (2019). https://doi.org/10.1080/14733315.2018.1435026\u003c/li\u003e\n\u003cli\u003eWang, N., Ernle, L., Beko, G., Wargocki, P., Williams, J. Emission rates of volatile organic compounds from humans. \u003cem\u003eEnviron. Sci. Technol\u003c/em\u003e. \u003cstrong\u003e56 \u003c/strong\u003e(8), 4838-4848 (2022). https://doi.org/10.1021/acs.est.1c08764\u003c/li\u003e\n\u003cli\u003ehttps://www.acuitybrands.com/resources/technical-resources/visual-lighting-software\u003c/li\u003e\n\u003cli\u003eANSI/ASHRAE. Standard 62.1-2019: Ventilation for acceptable indoor air quality (\u003cem\u003eASHRAE\u003c/em\u003e, Atlanta. GA, USA\u003cem\u003e,\u003c/em\u003e 2019).\u003c/li\u003e\n\u003cli\u003eThe Lancet COVID-19 commission, \u003cem\u003eProposed non-infectious air deliver rates (NADR) for reducing exposure to airborne respiratory infectious diseases\u003c/em\u003e. 2022. https://covid19commission.org/safe-work-travel\u003c/li\u003e\n\u003cli\u003eRim, D., Novoselec, A., \u0026amp; Morrison, G. The influence of chemical interactions at the human surface on breathing zone levels of reactants and products. \u003cem\u003eIndoor Air\u003c/em\u003e. \u003cstrong\u003e19\u003c/strong\u003e (4), 324-334 (2009). https://doi.org/10.1111/j.1600-0668.2009.00595.x\u003c/li\u003e\n\u003cli\u003eNicas, M., Nazaroff, W. W., Hubbard, A. Toward understanding the risk of secondary airborne infection: emission of respirable pathogens. \u003cem\u003eJ. Occup. Environ. Hyg\u003c/em\u003e. \u003cstrong\u003e2\u003c/strong\u003e (3), 143-154 (2005). https://doi.org/10.1080/15459620590918466\u003c/li\u003e\n\u003cli\u003eLin, Z., Wang, J., Yao, T., Chow, T. T. Investigation into anti-airborne infection performance of stratum ventilation. \u003cem\u003eBuild. Environ\u003c/em\u003e. \u003cstrong\u003e54\u003c/strong\u003e, 29-38 (2012). https://doi.org/10.1016/j.buildenv.2012.01.017\u003c/li\u003e\n\u003cli\u003eNazaroff, W. W., Weschler, C. J. Indoor ozone: Concentrations and influencing factors. \u003cem\u003eIndoor air\u003c/em\u003e. \u003cstrong\u003e32\u003c/strong\u003e (1), e12942 (2022). https://doi.org/10.1111/ina.12942\u003c/li\u003e\n\u003cli\u003ePark, S., Lee, S., Yeo, M. S., Rim, D. Performance of a heat recovery ventilation system for controlling human exposure to airborne particles in a residential building. \u003cem\u003eBuild. Environ\u003c/em\u003e. \u003cstrong\u003e239\u003c/strong\u003e, 110412 (2023). https://doi.org/10.1016/j.buildenv.2023.110412\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Indoor air quality, COVID-19, secondary chemistry, ozone, germicidal ultraviolet, UVC 222 nm","lastPublishedDoi":"10.21203/rs.3.rs-4421781/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4421781/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe far-UVC (222 nm) system has emerged as a solution for controlling airborne transmission, yet its effect on indoor air quality 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) with the air quality model. Our findings reveal that the ceiling-mounted type reduces human exposure to airborne pathogens by up to 80%. For all the lamp positions, the O\u003csub\u003e3\u003c/sub\u003e concentration in the breathing zone increases by 4\u0026ndash;6 ppb after one hour of operation. However, the stand-alone type poses a risk of exposing occupants to elevated levels of O\u003csub\u003e3\u003c/sub\u003e, as it creates a high concentration zone (\u0026gt;\u0026thinsp;25 ppb) near the lamp. Moreover, ventilation plays a crucial role in determining human exposure to airborne pathogens and secondary contaminants. Increasing the ventilation rate from 0.7 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 4 h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e reduces airborne pathogen and secondary contaminant concentrations by up to 90%. However, caution is warranted as it could also lead to elevated O\u003csub\u003e3\u003c/sub\u003e indoors, particularly in high outdoor O\u003csub\u003e3\u003c/sub\u003e conditions.\u003c/p\u003e","manuscriptTitle":"Human exposure to air contaminants under the far-UVC system operation in an office: Effects of lamp position and ventilation condition","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-05 18:10:08","doi":"10.21203/rs.3.rs-4421781/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-16T12:57:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-29T07:23:55+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-07T08:33:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"223330954816652653599323182107603077592","date":"2024-06-03T17:18:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"9462159160840519851187958922056232345","date":"2024-06-03T14:11:14+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-01T10:17:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-01T10:14:43+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-05-23T10:39:52+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-23T10:37:32+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-05-15T01:01:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"af43115d-2c90-4d67-8709-d078fd5694b7","owner":[],"postedDate":"June 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":32774135,"name":"Earth and environmental sciences/Environmental sciences"},{"id":32774136,"name":"Physical sciences/Chemistry"},{"id":32774137,"name":"Physical sciences/Engineering"},{"id":32774138,"name":"Physical sciences/Mathematics and computing"}],"tags":[],"updatedAt":"2024-10-21T16:12:37+00:00","versionOfRecord":{"articleIdentity":"rs-4421781","link":"https://doi.org/10.1038/s41598-024-75245-z","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-10-18 15:57:35","publishedOnDateReadable":"October 18th, 2024"},"versionCreatedAt":"2024-06-05 18:10:08","video":"","vorDoi":"10.1038/s41598-024-75245-z","vorDoiUrl":"https://doi.org/10.1038/s41598-024-75245-z","workflowStages":[]},"version":"v1","identity":"rs-4421781","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4421781","identity":"rs-4421781","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}