Summary of Our Chamber Burn Aerosol Optics Results: Multispectral measurements of light absorption and scattering, and RH dependence of measured light absorption

Kristin Lewis (UNR Atmospheric Sciences Grad Student), Multiwavelength Photoacoustic Measurements of Light Absorption and Scattering by Wood Smoke Kristin Lewis (UNR Atmospheric Sciences Grad Student), P. Arnott H. Moosmüller

Schematic of Photoacoustic Instrument 870 nm 405 nm

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 A very interesting case of smoke aerosol with very low single scattering albedo, yet very large hygroscopic growth for scattering is presented. Several samples of chamise (Adenostoma fasciculatum), a common and often dominant species in California chaparral, were recently burned at the USFS Fire Science Laboratory in Missoula Montana, and aerosol optics and chemistry were observed, along with humidity- dependent light scattering, absorption, and particle morphology. Photoacoustic measurements of light absorption by two instruments at 870 nm, one on the dry channel, one on the humidified channel, showed strong reduction of aerosol light absorption with RH above 65 percent, and yet a strong increase in light scattering was observed both at 870 nm and 550 nm with nephelometers. Multispectral measurements of aerosol light absorption indicated an Angstrom coefficient for absorption near unity for the aerosols from chamise combustion. It is argued that the hygroscopic growth of scattering is due to uptake of water by the sulfur bearing aerosol. Furthermore, the reduction of aerosol light absorption is argued to be due to the collapse of chain aggregate aerosol as the RH

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 `

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

Conclusion Inorganic content of woodsmoke causes fractal chains to collapse with RH increasing above 50-65%. This is very likely an irreversible change. 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. Photoacoustic response: Heat and mass transfer by evaporation. Light absorption -> both pathways in nature as well, not just heat transfer. 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