Long Range Transport
Mechanism
Regional Scale Dispersion Processes
Day Time Mixing
Random Mixing
Vertically distributes
pollutants
Wind Shear
Axial Mixing
Horizontally
Spreads pollutants
Wind Veer
Axial Mixing
Horizontally
redistributes pollutants
The three transport processes that shape regional dispersion are
wind shear, veer, and eddy motion or random mixing.
Homogeneous hazy airmasses are create through shear and veer
at night followed by vigorous vertical mixing during the day.
Regional Scale Dispersion
The degree of of the airmass spreading after a day of transport is
independent of the horizontal eddy diffusivity coefficient
Airmass History Model Comparison
HY-SPLIT Vs. CAPITA Monte Carlo Model
HY-SPLIT:
NGM wind fields, no mixing
Monte Carlo Model:
NGM wind fields, mixing
At times individual Airmass
histories compared very well
At times individual Airmass
histories compared very poorly
Local Flows
• Current regional scale
models poorly capture
local flows
– Complex Terrain
– Land Water Boundaries
– Near source impact
• Concentration are due
to local and regional
contributions
Blumenthal et al., 1997
Monte Carlo Transport Animations