Training on atmospheric dispersion in urban environments
Glossary
Atmospheric dispersion model
A computerized mathematical representation of the physics governing the transport and the dispersion of a pollutant in the atmosphere.
Building wake
An area of strong turbulence and downwash mixing caused by a negative pressure zone on the side of a building.
Diffusion
Clean air mixing with contaminated air through the process of molecular motion. Diffusion is a very slow process compared to turbulent mixing.
Dry deposition
The accumulation of particles as they come into contact with soil, water or vegetation on the Earth's surface.
Eulerian dispersion model
The pollution distribution is described by changing concentrations at discrete points on a fixed grid.
Gaussian plume
A plume within which the pollutants are distributed vertically and horizontally in a Gaussian (or normal) manner about the plume centreline.
Lagrangian model
The pollution distribution is described by a set of discrete particles or puffs, by following their trajectories.
Plume
A mostly horizontal (sometimes initially vertical) stream of air pollutant that is being blown from a source (Definition adapted from The
Glossary of Meteorology, American Meteorological Society).
Prevailing wind
An area-averaged wind specified over the urban area.
Streamline
A line with its tangent at any point in a fluid parallel to the instantaneaous velocity of the fluid at that point.
Turbulence
Small-scale atmospheric motions that tend to mix pollutants through the air.
Wet deposition
Removal of pollutants through scavenging by falling raindrops.
Wind direction shear
A tendency for wind direction to turn with height.
Acronyms
CBRN
Chemical, Biological, radiological and Nuclear
CUDM
Canadian Urban Dispersion Modeling System
EERS
Environmental Emergency Response Section
MLCD
Modèle Lagrangien Courte Distance
MLDPn
Modèle Lagrangien de Dispersion de Particules