1. 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

2. People and Instruments

3. Missoula Wood Smoke Optics and Chemistry Experiment 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… Optical, chemical, and microphysical properties of varied wood smoke aerosols were measured at the Missoula Fire Sciences Laboratory June 2006. For each of the 16 fuel types, 200 grams of fuel were ignited. The smoke was contained in a burn chamber and sampled for two hours.

4. Photoacoustic Instrument Schematic: First Measurements with a Multi-Wavelength Photoacoustic Instrument for Aerosol Light Scattering And Absorption

5. Angstr ö m Coefficients and Single Scattering Albedo Measurements at 2 wavelengths are used to obtain a, b, c, and d Angstr ö m coefficients for absorption and scattering. The typical assumption for absorption is d = 1 for elemental carbon. Single scattering albedo is obtained at each wavelength.

6. 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. Absorption by Wood Smoke

11. 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.