Page 343 - Fundamentals of Air Pollution 3E

298 19. Transport and Dispersion of Air Pollutants

w, wind speed, m s ~ l
a y, standard deviation of horizontal distribution of plume concentra-
tion (evaluated at the downwind distance x and for the appropriate
stability), m
cr v standard deviation of vertical distribution of plume concentration
(evaluated at the downwind distance x and for the appropriate
stability), m
L, mixing height, m
h, physical stack height, m
H, effective height of emission, m
x, downwind distance, m
y, crosswind distance, m
z, receptor height above ground, m
The concentration x resulting at a receptor at (x, y, z) from a point source
located at (0, 0, H) is given by one of the three following equations. (Meth-
ods for obtaining values for the dispersion parameters cr y and cr, in the
following equations are discussed later in this chapter.)
For stable conditions or unlimited vertical mixing (a very high mixing
height), use

where

Note that if y = 0, or z = 0, or both z and H are 0, this equation is greatly
simplified. For locations in the vertical plane containing the plume center-
line, y - 0 and g^ = 1.
For unstable or neutral conditions, where cr z is greater than 1.6L, use

For these large cr z values, eddy reflection has occurred repeatedly both at
the ground and at the mixing height, so that the vertical expanse of the
plume has been uniformly mixed through the mixing height, i.e., IIL.
For unstable or neutral conditions, where «r z is less than 1.6L, use the
following equation provided that both H and z are less than L;

where