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. Moosm ü ller

Light absorbing particles in the Atmosphere Produced by incomplete combustion of carbonaceous fuels. “Black Carbon” is operational definition: Amount of pure graphitic carbon particulate that would produce same absorption as aerosol sample. Graphitic Carbon Aerosol  Light absorption proportional to mass concentration  Inverse dependence of absorption on wavelength Example: B abs (405 nm) ≈ 2.15 × B abs (870 nm) Complications: Particle size, index of refraction, aging, organic materials

870 nm Schematic of Photoacoustic Instrument 405 nm

Missoula Fire Experiment Aerosol Smoke Properties Measured  Optics, chemistry, morphology and size For each of 16 fuel types 200 grams of fuel were ignited  Ponderosa, Lodgepole, Southern and Juniper Pines, Rice Straw, Chamise, Duffs, Palmetto, Fern, Manzanita and other shrubs. Smoke was contained in the burn chamber (60’ tall x 40’ x 40’) and sampled for two hours

Chamber Burns, Aerosol Optics and Microphysics

Informative Quantities Single Scattering Albedo  Ratio of scattering to extinction B abs = coefficient of scattering B sca = coefficient of absorption B ext = coefficient of extinction  Example: SSA = 0.75 indicates ratio of scattering to absorption is 3:1  Single scattering albedo is obtained at each wavelength

Informative Quantities Angström Coefficient of Absorption α = Angström Coefficient B abs = coefficient of absorption λ = wavelength of incident light Absorption values at two wavelengths allow for calculation of Angstrom Coefficient Recall:  α = 1 for pure elemental carbon aerosol … common assumption!

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 Winter Physics Department, University of Nevada Reno, Reno NV USA Derek Day National 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 Trimborn Aerodyne 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. Contours are the scattering enhancement factor. It is larger than the absorption factor.

Schematic to Measure Aerosol Optics as a function of RH.

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 %

Aerosol Composition for Collapsing and Non- Collapsing Aerosol.

Simple Collapsed Sphere Absorption Analysis

` Example of Dry Chamise Particle SEM Image

` Another Example of Dry Chamise Particle SEM Image

` Example of Chamise Particle SEM Image After H20 Vapor Applied at 85%

` Another Example of Chamise Particle SEM Image After H20 Vapor Applied at 85%

Hygroscopicity-Tandem-Differential-Mobility-Analyzer (HTDMA) From MONODISPERSE AEROSOL FROM DMA 1. MEASURE THE HUMIDIFIED PARTICLE SPECTRUM WITH DMA 2.

Conceptual Examples of HTDMA Measurements From

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

Conclusion 1.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