Calculation of wildfire Plume Rise

1
Calculation of wildfire Plume Rise

• Bo Yan
• School of Earth and Atmospheric Sciences
• Georgia Institute of Technology

2
Outline

• Introduction
• Fundament of principles
• Calculation of plume rise of wild fire
• Calculation of wildfire plume rise
• Case study
• Conclusions

3
Introduction of plume rise

• Plume rise - the height to which a plume emitted
  from an elevated source will rise.

Importance to the estimation of ambient
pollutant concentration, impact on the local and
distant environment.
Affected by the initial sources conditions (exit
velocity and temperature difference between the
plume and the air), the stable class and
stratification of the atmosphere, and the wind
field.
4
General calculation of plume rise

• Basic formulas of plume rise

5
General calculation of plume rise (cont)
6
Calculation of fire-plume rise

• Features of wild land fire plume
• - can not be treated in the same sense as
  those stack
• point sources, but usually be considered
  as an area
• source.
• - with a low initial momentum, the wildfire
  plume rise is
• dominated by the buoyancy.
• - continue near-surface release.

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Calculation of fire-plume rise

• Basic equation

?h the plume rise of fire plume, m x the
downward distance, r0 fire radius, m K the
velocity ratio, ( ) U 10-m wind speed, m/s ß
the entrainment coefficient (ß0.6) F the
Froude number, w0 the initial vertical
velocity, m/s ? a ambient density, kg/m3 ?? the
initial density difference between ambient air
and the fire plume. (?a-?p) TP, Ta
temperature of plume and ambient respectively,
K rP the radius of fire, m Qh the heat release
rate, J/s
8
Different cases of calculation of fire-plume rise

• Stable conditions
• Plume rise is limited by thermal
  stratification

?hf is the final rise, m N is the Brunt Vasaila
frequency
9
Different cases of calculation of fire-plume
rise (cont)

• Neutral conditions
• Ambient turbulence limits the final plume
  rise by breaking up the plume

(Briggs, 1984)
u friction velocity, m/s
10
Different cases of calculation of fire-plume
rise (cont)

• Unstable conditions
• Plume rise is also limited by turbulence

(Briggs, 1989
Weil, 1988)
zi inversion height, m w the convection
velocity scale, m/s
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Case study

• CAMx (comprehensive air quality model with
  extensions)

Plume characteristics Temperature of
release Radius of wild fire
Heat release Exit vertical velocity
Meteorological data Wind speed,
Ambient temperature Mixing height
Surface heat flux

Calculation of plume rise
12
Case study (cont)
13
Case study (cont)

• The calculation value shows that trend of plume
  rise with low height at night time and peak
  during the late afternoon

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Conclusions

• Basic concept about plume rise was introduced
  General calculation of plume rise was described
• Wildfire plume rise calculation was specifically
  discussed Based on three conditions,
  calculations were modified
• The basic theory of the plume rise model (CAMx)
  is limited to assumptions of uniform wind field
  and constant stability in the atmospheric layers.

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References

• Uarporn Nopmongcol. Plume rise model for Forest
  Fire Using ArcGIS Modeling Tool.
• www.utexas.edu/gis/gishydro03/classroom/trm
  proj
• Brown, et al. Fireplume model for plume
  dispersion from fires Application to uranium
  hexafluoride cylinder fires
• www.osti.gov/dublincore/gpo/servlets/purl/5
  10554-2x6vjV
• Seinfeld J.H. Atmospheric chemistry and physics
  from air pollution to climate change. 1997