A novel VOC breath tracer method to evaluate indoor respiratory exposures in the near- and far-fields

Several studies suggest that far-field transmission (> 6 ft) explains the significant number of COVID-19 superspreading outbreaks. Therefore, quantitative evaluation 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. 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 2.5 ft, 5 ft, 7.5 ft from the participant, as well as in the exhaust plenum of the chamber. We observed that 2.5 ft trials had substantially (~36–44%) higher concentrations than other distances during the first 20 minutes of experiments, highlighting the importance of the near-field 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 2.5 ft, 5 ft, and 7.5 ft were only ~18%, ~11%, and ~7.5% higher than volume-averaged concentrations, respectively. Our findings highlight the importance of far-field transmission of airborne pathogens including SARS-CoV-2, which need to be considered in public health decision making.