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J Expo Sci Environ Epidemiol

Title:		A novel VOC breath tracer method to evaluate indoor respiratory exposures in the near- and far-fields; implications for the spread of respiratory viruses
Author(s):		Parhizkar H; Fretz M; Laguerre A; Stenson J; Corsi RL; Van Den Wymelenberg KG; Gall ET;
Address:		"Institute for Health and the Built Environment, University of Oregon, Portland, OR, 97209, USA. Energy Studies in Buildings Laboratory, University of Oregon, Eugene, OR, 97403, USA. Biology and the Built Environment Center, University of Oregon, Eugene, OR, 97403, USA. Department of Mechanical and Materials Engineering, Portland State University, Portland, OR, 97201, USA. Department of Civil and Environmental Engineering, University of California, Davis, Davis, CA, 95616, USA. Institute for Health and the Built Environment, University of Oregon, Portland, OR, 97209, USA. kevinvdw@uoregon.edu. Energy Studies in Buildings Laboratory, University of Oregon, Eugene, OR, 97403, USA. kevinvdw@uoregon.edu. Biology and the Built Environment Center, University of Oregon, Eugene, OR, 97403, USA. kevinvdw@uoregon.edu"
Journal Title:		J Expo Sci Environ Epidemiol
Year:		2023
Volume:		20221123
Issue:		3
Page Number:		339 - 346
DOI:		10.1038/s41370-022-00499-6
ISSN/ISBN:		1559-064X (Electronic) 1559-0631 (Print) 1559-0631 (Linking)
Abstract:		"BACKGROUND: Several studies suggest that far-field transmission (>6 ft) explains a significant number of COVID-19 superspreading outbreaks. OBJECTIVE: Therefore, quantifying the ratio of near- and far-field exposure to emissions from a source is key to better understanding human-to-human airborne infectious disease transmission and associated risks. METHODS: In this study, we used an environmentally-controlled chamber to measure volatile organic compounds (VOCs) released from a healthy participant who consumed breath mints, which contained unique tracer compounds. Tracer measurements were made at 0.76 m (2.5 ft), 1.52 m (5 ft), 2.28 m (7.5 ft) from the participant, as well as in the exhaust plenum of the chamber. RESULTS: We observed that 0.76 m (2.5 ft) trials had ~36-44% higher concentrations than other distances during the first 20 minutes of experiments, highlighting the importance of the near-field exposure relative to the far-field before virus-laden respiratory aerosol plumes are continuously mixed into the far-field. However, for the conditions studied, the concentrations of human-sourced tracers after 20 minutes and approaching the end of the 60-minute trials at 0.76 m, 1.52 m, and 2.28 m were only ~18%, ~11%, and ~7.5% higher than volume-averaged concentrations, respectively. SIGNIFICANCE: This study suggests that for rooms with similar airflow parameters disease transmission risk is dominated by near-field exposures for shorter event durations (e.g., initial 20-25-minutes of event) whereas far-field exposures are critical throughout the entire event and are increasingly more important for longer event durations. IMPACT STATEMENT: We offer a novel methodology for studying the fate and transport of airborne bioaerosols in indoor spaces using VOCs as unique proxies for bioaerosols. We provide evidence that real-time measurement of VOCs can be applied in settings with human subjects to estimate the concentration of bioaerosol at different distances from the emitter. We also improve upon the conventional assumption that a well-mixed room exhibits instantaneous and perfect mixing by addressing spatial distances and mixing over time. We quantitatively assessed the exposure levels to breath tracers at alternate distances and provided more insights into the changes on 'near-field to far-field' ratios over time. This method can be used in future to estimate the benefits of alternate environmental conditions and occupant behaviors"
Keywords:		"*Air Pollutants/analysis *Air Pollution, Indoor Breath Tests Volatile Organic Compounds Aerosols *Disease Transmission, Infectious Bioaerosol Covid-19 Healthy buildings Infectious disease PTR-ToF-MS Risk;"
Notes:		"MedlineParhizkar, Hooman Fretz, Mark Laguerre, Aurelie Stenson, Jason Corsi, Richard L Van Den Wymelenberg, Kevin G Gall, Elliott T eng P30 ES030287/ES/NIEHS NIH HHS/ Evaluation Study Research Support, N.I.H., Extramural 2022/11/25 J Expo Sci Environ Epidemiol. 2023 May; 33(3):339-346. doi: 10.1038/s41370-022-00499-6. Epub 2022 Nov 23"