Dispersion coeffs. for soot particles in smoke plumes from refinery chimneys were detd. directly without ref. to the contour of the plume by using a digital image processing system of time exposure negatives. These coeffs. depended on the distance from the chimney and agreed well with literature data for built-up areas and with the corresponding dispersion coeffs. of the Refinery Law and the air regulation amendments. The vertical eddy diffusivities were 10-110 m2 s calcd. from the dispersion coeffs. and were strongly dependent on stability for labile and neutral stability classes and only somewhat dependent for slightly and very stable classes of dispersion, as defined by the Rifinery Law.