The techniques used to represent point sources in numerical air pollution models have received little attention.However, an inadequate representation of these sources can lead to significant loss of solution accuracy. Kasibhatla et al. (1988, Atmospheric Environment 22, 75-82) have performed a parametric error analysis for the two-dimensional transport of an inert species from an infinite line source. This paper extends the analysis to three-dimensional problems. Numerical results for an inert plume emanating from a single point source shown that the radio of the advection time scale to the turbulent time scale in the vertical direction, KzΔx/uΔy2, as well as the ratio of the advection time scale to the turbulent diffusion time scale in the cross-wind direction, KyΔx/uδy2, have an effect on solution accuracy. In addition, comparisons between the volume-averaged representation of a point source and the use of an irregular grid for point source representation demonstrate that, near the source, improved results can be obtained by placing a node at the source location. Numerical results for the case in which the wind velocity vector is not aligned with tghe grid lines indicate that the cross-derivative diffusion term can be negleted without loss of accuracy. © 1990.