November 5, 2024
How Far-UVC Lighting Impacts Indoor Air Quality
Study explores how ceiling-mounted 222 nanometer lights affect pathogens and ozone exposure
In the study, "Human Exposure to Air Contaminants Under Far-UVC System Operation in an Office: Effects of Lamp Position and Ventilation Condition," researchers Seongjun Park from Harvard T.H. Chan School of Public Health and Donghyun Rim from Pennsylvania State University investigate the use of far-UVC light (at 222 nm) in office environments for airborne pathogen disinfection and its impact on indoor air quality.
Far-UVC technology has gained interest for its ability to inactivate viruses and bacteria without the skin-damaging risks associated with traditional UVC wavelengths (254 nm). However, questions remain regarding its optimal placement and effects on indoor ozone (O₃) levels. This study uses computational fluid dynamics (CFD) simulations to explore how lamp positioning and ventilation rates influence disinfection efficacy and contaminant levels.
Key Findings on Lamp Placement and Air Quality
The study tested three configurations for far-UVC lamps: ceiling-mounted, wall-mounted, and stand-alone. The findings highlighted the importance of lamp placement in optimizing pathogen reduction and minimizing exposure to byproducts.
- Ceiling-Mounted Configuration: The ceiling-mounted lamp showed the highest effectiveness, reducing airborne pathogens by up to 80% compared to settings without UV light. This position leveraged room airflow, pushing pathogens toward the upper region, where they are more effectively exposed to UV. By positioning the lamp overhead, pathogen exposure within occupants' breathing zones was minimized, a significant consideration in reducing respiratory infection risks.
- Ozone Concentration: One drawback of far-UVC systems is their capacity to generate ozone, a secondary contaminant formed when far-UVC light photolyzes oxygen. Over an hour of operation, O₃ levels in the breathing zone increased by 4–6 parts per billion (ppb). This rise was most pronounced in the breathing zones near the lamps, especially with stand-alone types. High O₃ concentrations could reach 25 ppb directly around the lamp, raising potential health concerns.
- Ventilation Effects: Ventilation played a critical role in moderating air quality. The study tested various ventilation rates, from 0.7 to 4 air changes per hour (ACH). Increasing ventilation significantly diluted airborne pathogens and lowered secondary contaminant concentrations, improving overall air quality. However, higher ventilation rates also introduced more outdoor ozone indoors, highlighting a trade-off in areas with elevated outdoor O₃ levels.
Far-UVC and Indoor Ozone Generation
The research highlights a key challenge with using far-UVC: while it effectively disinfects air, it also induces ozone formation. O₃, a respiratory irritant, can react with indoor volatile organic compounds (VOCs) to create additional pollutants like hydroxyl radicals (OH) and secondary organic aerosols (SOAs), which can be harmful. During far-UVC operation, OH levels were elevated near the lamps, especially in low-ventilation scenarios, potentially exacerbating indoor air quality concerns.
Interestingly, despite higher initial UV fluence rates in the breathing zone of stand-alone lamps, the ceiling-mounted configuration proved most efficient in reducing pathogen exposure. This is due to its ability to align with the natural upward airflow patterns within rooms, which carries pathogens upward and out of the direct breathing zones of seated occupants.
Practical Implications for Lighting and HVAC Design
This research provides valuable insights for integrating far-UVC technology in commercial and office spaces:
- Ceiling-Mounted Lamps: This configuration is preferable for reducing pathogen exposure while mitigating high ozone concentrations near occupants. It positions UV light away from direct human exposure zones, aligning with air currents to capture more pathogens.
- Ventilation Considerations: Enhancing indoor ventilation effectively reduces airborne pathogen concentrations and lowers the accumulation of contaminants. However, facilities should be cautious about potential increases in indoor ozone levels if outdoor air is high in ozone. Balanced ventilation strategies, including filtration, might be necessary to optimize indoor air quality.
In summary, the study suggests that ceiling-mounted far-UVC systems are optimal for pathogen control in office settings, particularly when paired with adequate ventilation to manage secondary contaminants. These findings could guide future installations in high-occupancy spaces, balancing disinfection goals with air quality concerns.
