Decay rates of two tracer gases compared to DNA-tagged liquid aerosol tracer particles: Impact of varying dilution rate and filtration

Current gas-and aerosol-based tracers do not adequately simulate the emission and transport of liquid aerosols containing a pathogen indoors. To evaluate a liquid aerosol tracer containing synthetic DNA, the tracer was emitted in a chamber to measure changes in decay rates as outdoor air dilution rate and filter rating varied. DNA tracer concentration decay rates were compared to decay rates of size distributions of liquid tracer aerosols and two tracer gases (CO2 and SF6) to characterize the evolution of the particle size distribution simulated by the aerosols containing DNA tracer compared to common air change rate measurements. The effect of dilution ventilation on tracer decay rates was assessed at four air change rates using HEPA-filtered outdoor air (0, 1.3, 2.5, and 4.2 ACH), and the simultaneous impact of filtration of recirculated air (0, 1.3, 2.5, and 4.2 ACH) was tested using MERV8 and MERV13 filters. DNA tracer concentrations decayed at a rate comparable to liquid aerosols of 5–25 μm in diameter. Filter type did not consistently impact the rate of coarse particle or DNA tracer removal, though differences were observed for fine aerosols. Results indicate DNA-tagged tracer aerosols can simulate liquid aerosol emission and transport in a room, and the effectiveness of aerosol control strategies can be evaluated by observing the decay rate of DNA tracer concentrations.