Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

Abstract

There is ongoing and rapid advancement in approaches to modelling the fate of exhaled particles in different environments relevant to disease transmission. It is important that models are verified by comparison with each other using a common set of input parameters to ensure that model differences can be interpreted in terms of model physics rather than unspecified differences in model input parameters. In this paper, we define parameters necessary for such benchmarking of models of airborne particles exhaled by humans and transported in the environment during breathing and speaking.

Modeling and experimental study of dispersion and deposition of respiratory emissions with implications for disease transmission

“…Estimates of SARS‐CoV‐2 viral load in respiratory fluid span many orders of magnitude, and the value depends on a number of factors including the source of the respiratory fluid, the stage of the disease, and the sampling method used to collect the data. Stettler et al 1 report values ranging from an average of 1.18 × 10 6 copies/ml of sputum to as high as 1.34 × 10 11 copies/ml based on data from nasopharyngeal and throat swabs, while Chen et al 53 report from a meta‐analysis of 64 studies that the 90th percentile viral load was 1 × 10 9.84 copies/ml. Information on the decay of virus in exhaled droplets is also sparse 54 .…”

“…Coughs are exhalations for their full duration which were approximated as a triangular wave having a duration of 0.4 s and a peak velocity at 0.08 s. 15,16 The carrier flow velocity was spatially varied over the mouth opening within the initial expansion angle, or half cone angle, of the jet, shown in Figure 2. These values were taken from Stettler et al 1 for speaking and singing and Gupta et al 15 for coughing. In addition to the humid air flow, an amount of 5% CO 2 45 was included in each carrier flow source term, to explore the dispersion of the carrier flow within the room.…”

“…The particles consisted of two components; a solid part (consisting of salts, proteins, and surfactant) specified as non‐volatile and a liquid part (water) which could evaporate into the Eulerian phase. All of the solids were grouped into the non‐volatile part, with a volume‐weighted density calculated from the average of the non‐volatile components 1 as shown in Table 1. The resultant average solids density was 1830 kg/m 3 , giving the particles initial mass fractions of 98.75% water and 1.25% solids.…”

“…Contact transmission may be by direct contact with droplets from a contaminated individual or indirect contact such as touching a contaminated surface (fomite transmission). Airborne transmission arises from pathogen‐laden exhaled aerosols which are inhaled 1 . Droplets and aerosols exhaled during normal activities (breathing, talking, singing, coughing, and sneezing) have a range of diameters from <1 μm to >100 μm, and this plays an important role in the routes by which infection could occur.…”

“…Airborne transmission arises from pathogen-laden exhaled aerosols which are inhaled. 1 Droplets and aerosols exhaled during normal activities (breathing, talking, singing, coughing, and sneezing) have a range of diameters from <1 μm to >100 μm, and this plays an important role in the routes by which infection could occur. Very large droplets (>100 μm), which may be able to carry a larger microbial load, typically follow a ballistic trajectory and are unlikely to fully evaporate before they deposit on surfaces or on a susceptible individual.…”