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

Kristin Lewis (UNR Atmospheric Sciences Grad Student), P. Arnott

H. Moosmüller

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

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.

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

Coated-Sphere influence of an aqueous coating on aerosol optics.

QuickTime™ and aGraphics decompressorare needed to see this picture.

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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

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Shell Absorption Influence Ratio

•Contours are the scattering enhancement factor. It is larger than the absorption factor.

MODEL

REALITY

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

Humidified Aerosol Light Absorption Measurements: Hmmm????

Humidified Aerosol Light Scattering Measurements: Business as Usual.

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

Aerosol Composition for Collapsing and Non-Collapsing Aerosol.

ChamiseBurn B

Non-Refractory Mass

OrganicsSulfateChloridePotassium

Ponderosa Pine Needles and BranchesBurn C

Non-Refractory Mass

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%

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.

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.

Composition from Aerodyne and CU Mass Specs

Change of Absorption with RH fRH =Babs

WET (RH)−BabsDRY(RH < 30%)

BabsDRY(RH < 30%)

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.

Burning Brazilian Forest near Ji Parana: Pyrocumulus

Courtesy Michael Welling, SMOCC 2002, Sept 25