To calculate steady state concentration from a point source
__without reflection__, equation will be given:

On the other hand, for steady state concentration from a point source
__with reflection__, equation will be given:

Where, Q is the emission strength of the source (mass/time) and *u*
is the average wind speed taken through the plume. H is the effective stack
height, H = h + D h.
The
virtual point source may lie somewhat upwind of the center line of the
stack position, but here, we assume the point is directly above the stack.

The units on the concentration C are determined by the units used to
express the quantities Q, u, s_{y}
and s _{z}. The
terms, s _{y} and
s _{z }are usually
given in meters, u is in meter per second, and Q is in gram per second.
The units on the concentration then become grams per cubic meter (g/m^{3}).
The equation describes the change in the concentration as the plume travels
in the downwind direction x and gradually disperses in the vertical (z)
and perpendicular to the direction of travel (the y direction).

To evaluate the standard deviations s_{y}
and s _{z}, the
wind speed, the time of the day and the cloud condition are needed.