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Nature of  source and terrain

Conditions

Distance of travel (km)

Property estimated

Uncertainty

  • 1. Ground level source on flat terrain
Overcast steady wind

Generally unstable

0.1-1 <3

Peak of time-mean (few minutes) crosswind distribution a <0.1

b 0.1

b 0.2

  • 2. Moderately elevated plume (50-100m) over flat terrain
Generally unstable 1 Distance of maximum.

Magnitude of maximum

b 0.3

b 0.35

  • 3. Buoyant elevated plume over irregular terrain
Unstable or windy

Any except stagnation

10 Distance of maximum hourly average.

Maximum hourly average.

Long term average maximum

a 0.3

b 0.45

a 0.35

b 0.5

c 0.1

  • 4. Plume in mixing layer
Unstable with inversion,

definite wind field

100 Peak of time-mean
(1 hr) crosswind distribution. 		d 2.
  • 5. Multiple sources in urban industrial complex
Any except stagnation 10 Long-term spatial mean

Individual site, value averaged over few hours

Extreme (1% of occasions) of few-hour average at individual site

c 0.2

b 1.

d 2.

  • 6. As in 5, but source inventory not specified
Any except stagnation 10 Daily mean averaged over 100 sites at 1 site b 0.25

b 0.35