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AGU Fall Meeting 2009 San Francisco CA ID# A11E-02

Wavelength Dependence of Aerosol Light Absorption in Urban and Biomass Burning Impacted Conditions: An Integrative Perspective. Paper A11E-02. W. Patrick Arnott Madhu Gyawali Kristin Lewis Hans Moosmüller. AGU Fall Meeting 2009 San Francisco CA ID# A11E-02. Atmospheric Science Program

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AGU Fall Meeting 2009 San Francisco CA ID# A11E-02

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  1. Wavelength Dependence of Aerosol Light Absorption in Urban and Biomass Burning Impacted Conditions: An Integrative Perspective. Paper A11E-02.W. Patrick ArnottMadhu GyawaliKristin LewisHans Moosmüller AGU Fall Meeting 2009 San Francisco CA ID# A11E-02 Atmospheric Science Program University of Nevada Reno, NV Division of Atmospheric Science Reno, NV

  2. Outline Introduction Measurements show that the wavelength dependence of aerosol light absorption from biomass burning can be quite different than typical urban aerosol. Model results suggest that some aspects of our conventional wisdom on this subject need adjustment. Conclusions

  3. Quantify Wavelength Dependence of Light Absorption by Aerosol Ångström Coefficient for Absorption. •  ≈ 1 for motor vehicle emission generated BC. • Biomass burning aerosols exhibit  as high as 3.5. • Depends on chemical composition and particle size and morphology. • We use measurements at 405 nm and 870 nm to determine 

  4. Optical Model for Light Absorption by Soot Bottom Line: Light absorption by fresh soot has =1 when m does not depend on wavelength.

  5. Photoacoustic Aerosol Optics Instrument 355 nm (new!) 405 nm,870 nm 532 nm 671 nm, 676 nm 1047 nm • Aerosol Absorption and • Scattering Coefficients f0 f0 + df

  6. Ångström Coefficient Example

  7. Example: Homogeneous Soot Sphere Calculation Mie Theory for Homogeneous Spheres

  8. Morphology Change Upon Humidification

  9. Example of Dry Chamise Particle SEM Image `

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

  11. Lead Experiments on People! Circa 1975!

  12. Particle Collapse Upon Humidification in the Lungs! Chamberlain, A. C., W. S. Clough, M. J. Heard, D. Newton, A. N. B. Stott, and A. C. Wells (1975), Uptake of lead by inhalation of motor exhaust, Proceedings of the Royal Society of London. Series B, Biological Sciences, 192, 77-110.

  13. Wildfire Smoke in Northern California During July 2008 • Around 3000 Individual Fires • Most of The Fires Were Triggered • By Lightning • Burned Area Around 4686 km2 Reno, NV Smoke San Francisco, CA 185 Miles Cloud Source: NASA California Wild Fires 2008 JULY-10, 2008 SEPT-22, 2008 Reno Days in Photographs: Similar Location and Sun Angle

  14. Aerosol Optics of July and August, 2008 Apparent Light Absorbing Organic Carbon (ALAOC) = Amplification Due to Absorbing and Non Absorbing Coatings on Black Carbon. Extinction = Scattering + Absorption Smoke+Urban Urban • Common Definition of Light Absorbing Organic Carbon • Assumes Inverse Wavelength Dependence for Light Absorption

  15. Aerosol Optics of July and August, 2008 Single Scattering Albedo (SSA) Angstrom Exponent of Absorption (AEA) Smoke+Urban Smoke+Urban Urban Urban

  16. Comparison With Lab Data Ångström Exponent of Absorption vs Single Scattering Albedo • July: Dominated • by pine burning aerosol • August: Dominated • by vehicle emissions

  17. Chemistry of Primary Smoke Emissions Ponderosa Pine Smoke Electron Microscopy Ponderosa Pine Smoke Composition Ponderosa Pine Smoke BC Is Hugely Coated With Organics Alexandar Laskin, PNNL, and Aerodyne Aerosol Mass Spec measurements

  18. Urban and Biomass Aerosol They are fundamentally different!

  19. Particle Morphology Strongly Affects the Ångström Exponent for Absorption: Computational Model Df=1.25 N=200 monomers 1.75 1.5 N=400 2 N=600 N=800 2.25 3 2.75 2.5 Ångström exponent of absorption vs fractal dimension. (From L. Liu and M. Mishchenko) Fractal aggregates of 200 monomers and various fractal dimensions. L. Liu , Michael I. Mishchenko, W. Patrick Arnott: Journal of Quantitative Spectroscopy & Radiative Transfer 109 (2008) 2656–2663

  20. Simulation of the Ångström Exponent of Absorption (405 and 870 nm) Core RI (1.55, 0.8i) Coating RI (1.5, 0.012i) at 405 nm and (1.5, 0.0i) at 870 nm (Coating absorbs at 405nm) Core RI (1.55, 0.8 i) Coating RI (1.5, 0.0i) (Non absorbing coating) Key Message: Coatings need not be absorbing to cause Ångström coefficients for absorption considerably different from 1.

  21. East Las Vegas NV, Jan-Feb 2003 Linear regression is a blunt tool !

  22. Summary The organic coating need not be intrinsically brown to observe the effects commonly referred to as those caused by brown carbon light absorption. Ångström coefficients as large as 1.6 are possible for some wood smoke even though the coating doesn’t absorb light. Aerosol morphology, size, and mixing state are of comparable importance with intrinsically ‘brown carbon’ coatings in explaining deviations of absorption Ångström coefficients from the canonical value of unity. Ångström coefficientsless than unity are not necessarily due to measurement precision and accuracy limitations.

  23. Thank for your Attention! Å = 1 ???

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