The assumptions that underlie the above equations are open for discussion. However, in the absence of better information, they represent our best estimate of the governing phenomena. While the mixing heights at night range from 100 to 500 meters, they approach 400 meters during clear, calm conditions. Therefore, from eq. Similarly, for the lateral dispersion in the urban boundary layer, ya is calculated using the SBL formulation given by eq.
Plume rise in the urban stable boundary layer is calculated from eq.
Use of this value for provides an appropriate near-neutral plume rise formulation that is expected within the nocturnal urban boundary layer. However, plume height in these conditions is not allowed to exceed 1.25 z iu Finally, in the nighttime urban boundary layer, plume meander is not modeled since this modified stable layer has many of the turbulent characteristics of a weak convective layer.