Transcript Multiwavelength Photoacoustic Measurements of Light

Multiwavelength Photoacoustic Measurements of
Light Absorption and Scattering by Wood Smoke
More Specific Title:
Evidence for light absorption by organic carbon species
in woodsmoke.
Kristin Lewis, William P. Arnott, and Stephanie Winter
University of Nevada Reno Physics Department
Hans Moosmuller
and the Desert Research Institute
Reno Nevada USA
Claudio Mazzoleni
Los Alamos National Laboratory
Los Alamos NM USA
People and Instruments
Missoula Wood Smoke Optics and Chemistry Experiment
•
Optical, chemical, and microphysical properties of varied wood smoke
aerosols were measured at the Missoula Fire Sciences Laboratory June
2006.
•
The
smoke was contained in a burn chamber and sampled for
two hours.
For each of the 16 fuel types, 200 grams of fuel were ignited.
• Photoacoustic instruments at
1047 nm
870 nm
780 nm
532 nm
405 nm
• 7 wavelength Aethalometer
• Aerodyne Mass Spec
• TDMA, CCN, SEM, CRD, Mercury, NO2, Ozone, TSI 3 lamba
Neph, Radiance Nephs, Scattering hygroscopicity, TEOM,
EC/OC, and more…
Photoacoustic Instrument Schematic: First Measurements with a
Multi-Wavelength Photoacoustic Instrument for Aerosol Light
Scattering And Absorption
405
nm
870 nm
Angström Coefficients and Single Scattering Albedo
Bsca
Babs
 


Bsca
Bext
a  b
d
c

Bsca
Bsca  Babs
Measurements at 2 wavelengths are used to obtain a, b, c, and d
Angström coefficients for absorption and scattering.
The typical assumption for absorption is d = 1 for elemental carbon.
Single scattering albedo is obtained at each wavelength.
Absorption by Wood Smoke
• For certain fuel types burned aerosol
light absorption did not display the 1/λ
dependence on incident wavelength
that is characteristic of small elemental
carbon aerosol.
• Absorption can be far more efficient at
the near-UV wavelength than in the
near-infrared.
Chamise: Single Scattering Albedo = 0.40 at 405 nm
60000
600
500
40000
400
30000
300
20000
200
UV - 370 nm
Blue - 470 nm
IR - 880 nm
405nm Absorption (Photoacoustic)
870nm Absorption (Photoacoustic)
10000
100
0
18:58
18:52
18:46
18:38
18:32
18:26
18:20
Time
18:12
18:06
18:00
17:54
17:46
17:40
17:34
17:28
17:20
17:14
17:08
0
Photoacoustic Babs (Mm -
50000
17:02
Aethalometer Black Carbon (ng m -3)
PA Absorption Angstrom Coef. = 1.18
Rice Straw Fuel: Single Scatter Albedo = 0.88 at 405 nm
50000
300
UV - 370 nm
Blue - 470 nm
40000
PA 405 nm
250
405 nm (Photoacoustic)
870 nm (Photoacoustic)
35000
30000
Aeth 370 nm
25000
Absorption
Angstrom Coef
= 2.81
200
150
20000
15000
100
Aeth 470 nm
10000
Aeth 880 nm
50
5000
0
32
8:
38
8:
44
8:
50
8:
58
9:
04
9:
10
9:
16
9:
22
9:
30
9:
36
9:
42
9:
48
9:
54
0
PA 880 nm
Time
Photoacoustic Babs (Mm -
IR - 880 nm
8:
Aethalometer Black Carbon (ng m-
45000
Ponderosa Pine,
mixed fuels
Chamise
Angstrom Coefficient for Absorbtion vs. Single
Scattering Albedo at 405 nm
3.50
Duff, ferns, and
rice straw.
3.00
Angstrom Coefficient of
Absorbtion
Ponderosa Pine,
mixed fuels
Chamise
Rice Straw
Ponderosa Pine Duff
Pine, evergreen, palm
mixed woods: needle
litter, branches, and
foilage.
2.50
Alaskan Duff
So. Californian
Manzanita
Sage & Rabbitbrush
Lignin
2.00
Brushes and Shrubs.
Lodgepole Pine,
mixed fuels
Utah Juniper,
foilage/twigs
Puerto Rico Fern
1.50
Chamise
Wax Myrtle,
branches/foilage
Southern Pine,
needles
Puerto Rico, mixed
woods
Palmetto
1.00
0.50
0.3
0.4
0.5
0.6
0.7
0.8
Single Scattering Albedo, 405 nm
0.9
1.0
Ceanothus
Ponderosa Pine,
mixed fuels
Chamise
Angstrom Coefficient for Absorbtion vs.
Single Scattering Albedo at 532 nm
2.4
Duff, ferns, and
rice straw.
2.2
Angstrom Coefficient of Absorbtion
(from Babs at 532 & 870 nm)
Ponderosa Pine,
mixed fuels
Chamise
Rice Straw
Ponderosa Pine Duff
2
Pine, evergreen, palm
mixed woods: needle
litter, branches, and
foilage.
1.8
Alaskan Duff
So. Californian
Manzanita
Sage & Rabbitbrush
1.6
Lignin
Brushes and Shrubs.
1.4
Lodgepole Pine,
mixed fuels
Utah Juniper,
foilage/twigs
Puerto Rico Fern
1.2
Chamise
1
Wax Myrtle,
branches/foilage
Southern Pine,
needles
Puerto Rico, mixed
woods
Palmetto
0.8
0.6
0.2
0.4
0.6
0.8
Single Scattering Albedo, 532 nm
1
Ceanothus
Conclusion
• Non-elemental-carbon components, such as organic
species, exist on smoke aerosol of certain fuel types and
preferentially absorb light at shorter wavelengths. In
addition to particle size, differences in refractive index at
widely differing wavelengths contribute to spectral
properties of the aerosol.
• Casual use of the inverse wavelength dependence of
aerosol light absorption in remote sensing retrievals
with sun photometers and satellite data can bring
errors of a factor of 6 in the UV and a factor of 2 in the
visible when compared with near IR absorption for
certain types of wood smoke.
ACKNOWLEDGEMENTS:
DOE ASP Program and the National Parks Service, field work.
NSF MRI program for instrument development.
All participants in the Missoula Fire Experiment.