A Footnote on the Role of Diffusiophoresis in Lung Depostion of Aerosols.

The importance of diffusiophoresis in influencing the deposition of aerosol particles in human and animal lungs has been speculated upon for some time. In this note, we present calculations for the magnitude of this effect based on typical flow behavior in human lungs. Two extreme cases of breathing rate are included, corresponding to sedentary situations and to vigorous exercise. In the upper portions of the respiratory system, the diffusiophoresis velocity caused by diffusion of water vapor into inhaled air should dominate the motion of particles smaller than ~ 1 µ, as compared with Brownian motion. Where diffusion of oxygen and carbon dioxide to and from the surfaces of the lower lung occurs, diffusiophoresis is much weaker but can become significant compared with Brownian diffusion for particles in the 0.1 - 1.0 µ size range, particularly for conditions of heavy exercise.