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

Informing Building Strategies to Reduce Infectious Aerosol Transmission Risk by Integrating DNA Aerosol Tracers with Quantitative Microbial Risk Assessment

“…The DNA tracer solution is emitted using a pneumatic nebulizer with a known volumetric emission rate. 11 Volumetric particle size distributions upon emission were measured in triplicate 0.15 m from the nebulizer with a Spraytec laser diffraction particle counter (0.12−1000 μm, Malvern Panalytical Ltd.) and converted to normalized particle number concentrations. The average relative particle number distribu-tion of the nebulizer is compared to a normalized distribution from the BLO trimodal model of cough aerosols in Figure S1.…”

“…Aerosolized DNA Tracer Removal Rate. Measuring bulk aerosolized DNA tracer removal rates (λ trc,meas ) in buildings, which accounts for the combined removal rates of ventilation, filtration, and deposition, can be accomplished using aerosolized tracer concentration decay techniques, 11 and we assume bulk aerosolized tracer removal rates are equivalent to bulk respiratory aerosol removal rates due to similarities in particle size distributions and composition. When aerosol tracer decay rates cannot be measured, gaseous tracer removal rates (λ gas ) or ventilation rates (q v /v r ) can be used to estimate tracer aerosol removal rates using the linear regression described in Section S6.…”

“…Upon incorporation of a tracer molecule into the liquid aerosol, such as nucleic acid sequences (i.e., synthetic DNA), such a tracer solution becomes quantifiable through quantitative polymerase chain reaction (qPCR). Aerosol tracers tagged with synthetic DNA were originally validated by Harding et al As currently deployed, a synthetic DNA tracer solution is aerosolized as a burst from a nebulizer, simulating the emission of aerosols similar in composition to and within the size distribution of respiratory aerosols produced during a cough or sneeze …”

“…Aerosol tracers tagged with synthetic DNA were originally validated by Harding et al 10 As currently deployed, a synthetic DNA tracer solution is aerosolized as a burst from a nebulizer, simulating the emission of aerosols similar in composition to and within the size distribution of respiratory aerosols produced during a cough or sneeze. 11 Presented is a framework for integrating QMRA model estimates of infectious aerosol transmission risk with filter sample-based measurements of aerosolized DNA tracers in buildings to inform the effectiveness of mitigation efforts. We derive a scaling factor for converting from time-integrated aerosolized DNA tracer concentrations to pathogen dose and infection risk using a bulk aerosol QMRA model for SARS-CoV-2.…”

“…We propose a method for combining airborne pathogen transmission risk modeling and physical tracer measurements for modeling the risk reduction that results from infectious aerosol exposure mitigation measures. This is accomplished by integrating quantitative microbial risk assessment (QMRA) − with aerosol concentrations of synthetic DNA tracers collected in buildings. − …”