This is pretty cool, and also seems pretty accessible for a “graphics thing.” Just a little calculus.

It would be kind of neat to have an example of a physical situation that produces each of the example functions (although I’m sure that isn’t always possible).

Can the effect of multiple fog emitters reasonably be modeled as the sum of their outputs? I guess for high densities, probably not (eventually the air will get saturated), but for low densities, probably yes…

For simple models (constant incoming radiance), you can indeed just add the optical depths from the different fog 'layers'. (90% sure but the maths is easy to check anyway, see https://forwardscattering.org/post/72)