To calculate the dispersion of flue gas from a single stack, it is concluded that the Sutton formula is convenient and sufficiently accurate at the present time. After considering a number of plume rise formulae, it was decided that a better fit to the available results for stacks producing gas quantities in the range 15–100 Nm 3/sec was obtained by a relationship of the form Δh = K Q 1 2 h u 1 4 in which Q h is the heat flux, and u the wind speed at the height of the top of the stack. This was suggested by regression analysis of the data. The incorporation of this formula into the Sutton equation leads finally to the following equation for the critical ground-level concentration of SO 2 from fossil fuel firing: C crit = 6.30 × 10 2.Q p[ 1 Q vΔT h ] 2 3 in which C crit is the critical ground-level concentration ( 1 2 hr samples) in mg m −3, Q v is the rate of production of pollutant (SO 2) in kg hr −1, Q v is the rate of production of total flue gas in Nm 3 hr −1, ΔT is the difference in temperature between the flue gas and the ambient air in °K and h is the stack height in metres. This equation is presented as a nomogram. It involves assuming an average value for the constant K in the plume rise formula, and takes Sutton's C z C y as 0.7, applicable for neutral conditions. The effect of other values of K (which can vary by ± 50 per cent about the mean) and C z C y on C crit , or on a value of h calculated to satisfy a specified value of C crit is shown by means of graphs of adjustment factors. For the calculation of stack heights in practical cases, it is considered that the intermediate value of h derived from the nomogram to satisfy a specified C crit should be doubled, to make reasonable allowance for low plume rises and high values of C z C y . This factor is necessarily tentative and might be capable of more precise evaluation on sites where adequate plume rise and meteorological data are available.