Deposition (aerosol physics)

[1] This is because very small particles coagulate in few hours until they achieve a diameter of 0.5 micrometres.

This can be predicted with the Stokes number Stk = S / d, where S is stopping distance (which depends on particle size, velocity and drag forces), and d is characteristic size (often the diameter of the obstacle).

Deposition due to Brownian motion obeys both Fick's first and second laws.

, where J is deposition flux, n is the initial number density, D is the diffusion constant and t is time.

This means that wet deposition is gravitational, Brownian and/or turbulent coagulation with water droplets.