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

Abstract

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.

Figure 1

Experimental setup, A) climate chamber, airflow distribution, as well as sampling location for each unique trial (modeled in Rhinoceros software), B) experimental procedure and the number of breath mints consumed by the participant for each trial.

Figure 2

A) Concentration of three target tracer compounds (menthol, menthone, and monoterpenes) in the headspace of a 250 mL glass chamber as a function the time when a breath mint is placed inside, B) Concentration of the three target compounds when the participant exhaled their breath once into the 250 mL chamber while consuming the breath mint.

Figure 3

Comparison of 2.5, 5, and 7.5ft trials normalized by volume-averaged concentration.