Dispersion parameters measured during neutral and stable conditions in Canada

Abstract

Plume spread parameters obtained during six years of research by the Canadian Combustion Research Laboratory (CCRL) have been evaluated and compared to the standard predictive relationships established by Pasquill and Gifford. The data correspond to neutral and stable conditions, Stability Class C to F but excludes any limited-mixing or layered atmosphere studies or situations where topography influences plume spread. In all, ten sources in five geographic regions were studied during Spring, Fall and Winter. The Pasquill-Gifford curves as modified by Bowne for rural conditions represent a convenient means of comparing the data obtained under corresponding stability and topographic conditions in Canada. The variation of measured horizontal spread parameters, oy with downwind distance differed significantly from the P/G curves, being wider by at least two stability classes for unstable/neutral i.e. A/B rather than C/D, and for stable, C rather than E. In the case of very stable F class, the measured a values corresponded to A class, six classes wider than expected. The vertical spread parameters, az were usually in agreement with P/G curves from 4 to 10 km from the source, closer to the source az was greater and farther from the source az was less than predicted. It was also found that the bulk Richardson number could be used to classify the plume spread parameters in a similar manner to the P/G stability classes.