Calculation of wildfire Plume Rise

Bo Yan

School of Earth and Atmospheric SciencesGeorgia Institute of Technology

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

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.

General calculation of plume rise

Basic formulas of plume rise

a

b

u

Exh

General calculation of plume rise (con’t)

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.

Calculation of fire-plume rise

Calculation of fire-plume rise

Basic equation

0

3

13

0

322

20

4

3 rr

KF

xrh

Δh : the plume rise of fire plume, mx: the downward distance, r0: fire radius, mK: the velocity ratio, ( )U 10-m wind speed, m/sβ : the entrainment coefficient (β=0.6)F : the Froude number,

w0 : the initial vertical velocity, m/s

ρ a: ambient density, kg/m3Δρ: the initial density difference between ambient air and the fire plume. (ρa-ρp)

TP, Ta : temperature of plume and ambient respectively, KrP: the radius of fire, mQh: the heat release rate, J/s

0w

U

2

120

2

g

wF a

2

6

0

108.8

PaP

Ph

rTTg

TQw

Different cases of calculation of fire-plume rise Stable conditions Plume rise is limited by thermal stratification

3

1

322

201.2

KFN

Urh f

Δhf is the final rise, m

N is the Brunt Vasaila frequency

2

1

z

gN

Different cases of calculation of fire-plume rise (con’t)

Neutral conditions Ambient turbulence limits the final plume rise by breaking

up the plume

322*

2076.0KFu

Urh f

(Briggs, 1984)

u*: friction velocity, m/s

Different cases of calculation of fire-plume rise (con’t) Unstable conditions

Plume rise is also limited by turbulence

5

3

322*

3

22

0

45.4

KFw

zUrh if

(Briggs, 1989; Weil, 1988)

zi : inversion height, m

w*: the convection velocity scale, m/s

3

1

''*

i

v

zwg

w

Case study CAMx (comprehensive air quality model with

extensions)

Meteorological data: Wind speed, Ambient temperature Mixing height Surface heat flux

Calculation of plume rise

Plume characteristics: Temperature of release Radius of wild fire Heat release Exit vertical velocity

+

Case study (con’t)Fireplume calculations

Aug 30, Fire ID 1033 , 1000 acres

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14 16 18 20 22time

plu

me

ris

e (

m.)

65

78

4

10

11

3

9

Fireplume calculations Sep 1, Fire ID 1094 , 800 acres

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14 16 18 20 22time

plu

me

ris

e (

m.)

11

54

6

3

2

Case study (con’t)The calculation value shows that trend of plume rise with low height at

night time and peak during the late afternoon

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.

References Uarporn Nopmongcol. Plume rise model for Forest Fire Using

ArcGIS Modeling Tool. www.utexas.edu/gis/gishydro03/classroom/trmproj

Brown, et al. Fireplume model for plume dispersion from fires: Application to uranium hexafluoride cylinder fires

www.osti.gov/dublincore/gpo/servlets/purl/510554-2x6vjV

Seinfeld J.H. Atmospheric chemistry and physics: from air pollution to climate change. 1997