Combined effect of relative humidity and temperature on expiratory particle dispersion.

Indoor ambient conditions such as relative humidity and temperature critically affect the evaporation, settling, and dispersion of expiratory particles. Accurate prediction of the complex interaction between these conditions and the turbulent exhalation jet is essential for assessing exposure risk to airborne pathogens in shared indoor environments. Capturing the spatiotemporal evolution of turbulent mixing and its influence on aerosol transport is therefore key to realistically modelling the physics of this process.



This work investigates the combined effect of relative humidity and temperature on expiratory particle dispersion during a speaking event. Three cases representative of realistic seasonal scenarios – winter, summer and tropical – are examined to assess and quantify how the rate of evaporation, aerosol transport, and local aerosol exposure are influenced by the coupled variations in relative humidity and temperature. A finite-difference large-eddy simulation in-house code is used to solve the filtered Navier-Stokes and energy equations on a staggered grid for the continuous (air) phase, while the dispersed phase (liquid particles) is modelled by a Lagrangian Particle Tracking algorithm, where the particles are composed of a binary water-NaCl solution. Realistic particle size distribution and emission rate are used, and the particle volume fraction is computed to quantify the spatiotemporal evolution of infection risk.