multiwavelength photoacoustic measurements of light absorption and scattering by wood smoke
DESCRIPTION
Summary of Our Chamber Burn Aerosol Optics Results: Multispectral measurements of light absorption and scattering, and RH dependence of measured light absorption. Multiwavelength Photoacoustic Measurements of Light Absorption and Scattering by Wood Smoke. - PowerPoint PPT PresentationTRANSCRIPT
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Summary of Our Chamber Burn Aerosol Optics Results: Multispectral measurements of light absorption and scattering, and RH dependence of measured light absorption
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Multiwavelength Photoacoustic Measurements of Light Absorption and Scattering by Wood Smoke
Kristin Lewis (UNR Atmospheric Sciences Grad Student), P. Arnott
H. Moosmüller
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Sample InletSample Outlet
Input
Coupler
Output
Coupler
Piezoelectric
Transducer
Microphone and
Surrounds
RESONATOR
SECTION
COUPLING
SECTION
COUPLING
SECTION
Photodetector
C osine-
Weighted
Sensor.
Scattering
Measurement.
Fiber-coupled
to PMT.
LASER 1
LASER 2
LASER 3
Fiber 1
Fiber 3
Fiber 2
Culmination
Fiber
405nm
870 nm870 nm
Schematic of Photoacoustic Instrument
405nm
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Summary
Non-black carbon components, such as organic species, exist on smoke particles of certain fuels.
These species preferentially absorb radiation in the ultra violet (at shorter wavelengths).
Casual use of the inverse wavelength dependence of aerosol light absorption in remote sensing 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.
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Observations of the REDUCTION Of Aerosol Light Absorption and INCREASE of Biomass Burning Aerosol
Light Scattering for Increasing Relative Humidity W. Patrick Arnott, Kristin Lewis, Guadalupe Paredes-Miranda, and Stephanie WinterPhysics Department, University of Nevada Reno, Reno NV USA
Derek DayNational Park Service, Fort Collins CO
Rajan K. Chakrabarty, Antony Chen, and Hans Moosmüller Desert Research Institute, Reno NV
Jose-Luis Jimenez, Ingrid Ulbrich, and Alex Huffman University of Colorado Boulder, CO
Timothy Onasch and Achim TrimbornAerodyne Research Inc Boston MA
Sonia Kreidenweis and Christian Carrico Department of Atmospheric Sciences, Colorado State University Fort Collins CO
Cyle Wold, Emily N. Lincoln, Patrick Freeborn, and Wei-Min Hao Fire Sciences Laboratory Missoula, MT
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Coated-Sphere influence of an aqueous coating on aerosol optics.
QuickTime™ and aGraphics decompressorare needed to see this picture.
0.01
0.1
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Aqueous Shell Thickness / Carbon Core Radius
11.11.21.31.41.51.61.71.81.9
1.3
1.4
1.5
2
4
4
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1012
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Shell Absorption Influence Ratio
•Contours are the scattering enhancement factor. It is larger than the absorption factor.
MODEL
REALITY
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Schematic to Measure Aerosol Optics as a function of RH.
Neph550 nm Sca
PA 870 nm Sca and Abs
PA 870 nm Sca and Abs
Neph550 nm Sca
PA 870 nm Sca and Abs
PA 870 nm Sca and Abs
SAMPLE INLET
DRY SIDE HUMID SIDE
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Humidified Aerosol Light Absorption Measurements: Hmmm????
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Humidified Aerosol Light Scattering Measurements: Business as Usual.
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Ponderosa Pine: No Change of Absorption or Scattering with RH to 85 %
Angstrom Coef Abs 405 and 870 nm
Angstrom Coef Sca 405 and 870 nm
Single Scatter Albedo 405 nm
1.71 1.22 0.87
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Aerosol Composition for Collapsing and Non-Collapsing Aerosol.
ChamiseBurn B
Non-Refractory Mass
OrganicsSulfateChloridePotassium
Ponderosa Pine Needles and BranchesBurn C
Non-Refractory Mass
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Simple Collapsed Sphere Absorption Analysis
d = monomer diameterN monomers
Collapsed Sphere?Diameter = d N1/3
Wave Skin Depth =λ
4π ni
=Coλλaπsed Sπhere Radius=D2
=dN1/3
2
Monomer diameter (nm)
Number of Monomers
Imag Ref Index
Wavelength (nm)
Skin Depth (nm)
Sphere
Diameter for
Radiative Transition
(nm) =Collapsed Particle
Diameter (nm)
50 250 0.44 870 157 315 31550 99 0.60 870 115 231 231
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Example of Dry Chamise Particle SEM Image
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Another Example of Dry Chamise Particle SEM Image
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Another Example of Chamise Particle SEM Image After H20 Vapor Applied at 85%
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HTDMA Growth Factors from Kip Carrico, CSU
Messages:
•100 nm chamise smoke particles grow much more than ponderosa pine smoke particles.
•(Chamise smoke particles likely good Cloud Condensation Nuclei.)
•No particle shrinkage.
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HTDMA Growth Factors from Kip Carrico, CSU
Messages:
•Larger chamise smoke particles first shrink with RH increase, then grow. (Likely evidence for collapse of the fractal structure with RH). These particles likely contribute most to light absorption.
•Larger ponderosa pine particles have modest growth with increasing RH.
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Composition from Aerodyne and CU Mass Specs
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Change of Absorption with RH fRH =Babs
WET (RH)−BabsDRY(RH < 30%)
BabsDRY(RH < 30%)
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Conclusion1. Inorganic content of woodsmoke causes fractal chains to collapse with RH increasing above 50-65%. This is very likely an irreversible change.
2. Hygroscopic growth of scattering and reduction of absorption was observed. It is likely that fractal collapse reduces the amount of elemental carbon available for light absorption. The next Missoula experiment should use multi-wavelength absorption and scattering and closure of CRD extinction and neph scattering to strengthen our understanding.
3. Photoacoustic response: Heat and mass transfer by evaporation. Light absorption -> both pathways in nature as well, not just heat transfer. 4. In nature also ???
Acknowledge DOE-ASP, National Park Service, and NSF MRI support.
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Burning Brazilian Forest near Ji Parana: Pyrocumulus
Courtesy Michael Welling, SMOCC 2002, Sept 25