I have a pollutant source (area source) on the bottom of a rectangular room. I just want to simulate how the pollutant diffuse in this room. From some preliminary simulation, it looks diffusion coefficient should be adjusted, but I don't know how to do it. If you have some ideas, please drop me a line. Thank you

I think of the diffusion coefficient as being the multiplier that sits infront of the diffusion term in the governing equations.

The Diffusion coefficient,(GAMMA), is rho*enul/prndtl(phi) for the variable phi. manipulating these values can change the diffusion coefficient in a limited way. if you wish to change it in an "anistropic" type manner, then you might have to use ground coding.