The necessary data is:
Physical stack height (m): This is the physical stack height in meters.
Stack gas exit velocity vs (m/s): This is the stack gas exit velocity. It can be around 15 m/s.
Stack gas exit temperature (K): The discharge concentration of the material of interest (pollutant or tracer) is defined as the excess concentration above any ambient concentration of that same material. 1g/m3=1ppm in air.
Stack inside diameter (m): This is the stack inside diameter.