Simulation of vertical concentration gradient of influenza viruses in dust resuspended by walking

Particles are resuspended from the floor by walking and are subject to turbulent transport in the human aerodynamic wake. These processes may generate a vertical concentration gradient of particles. To estimate the magnitude of turbulence generated by walking, we measured the velocity field in the wake from floor to ceiling at 10-cm intervals with a sonic anemometer. The resulting eddy diffusion coefficients varied between 0.06 and 0.20m(2)/s and were maximal at similar to 0.75-1m above the floor, approximately the height of the swinging hand. We applied the eddy diffusion coefficients in an atmospheric transport model to predict concentrations of resuspended influenza virus as a function of the carrier particle size, height in the room, and relative humidity, which affects the resuspension rate coefficient and virus viability. Results indicated that the concentration of resuspended viruses at 1m above the floor was up to 40% higher than at 2m, depending on particle size. For exposure to total resuspended viruses, the difference at 1 vs. 2m was 11-14%. It is possible that shorter people are exposed to higher concentrations of resuspended dust, including pathogens, although experimental evidence is needed to verify this proposition.