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 University of Nevada Reno, NV Division of Atmospheric Science Reno, NV

Outline 1. Introduction 2. Measurements show that the wavelength dependence of aerosol light absorption from biomass burning can be quite different than typical urban aerosol. 3. Model results suggest that some aspects of our conventional wisdom on this subject need adjustment. 4. Conclusions

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 

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

 Aerosol Absorption and Scattering Coefficients 355 nm (new!) 405 nm,870 nm 532 nm 671 nm, 676 nm 1047 nm Photoacoustic Aerosol Optics Instrument f0f0 f 0 + df

Ångström Coefficient Example

Example: Homogeneous Soot Sphere Calculation Mie Theory for Homogeneous Spheres

Morphology Change Upon Humidification

` Example of Dry Chamise Particle SEM Image

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

Soot Compaction from Sulfuric Acid and Water Vapors Fresh Soot After H 2 SO 4 Vapor Exposure Soot Compaction Process

Lead Experiments on People!

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, Particle Collapse Upon Humidification in the Lungs!

Smoke Reno, NVSan Francisco, CA 185 Miles Cloud JULY-10, 2008 SEPT-22, 2008 Reno Days in Photographs: Similar Location and Sun Angle Wildfire Smoke in Northern California During July 2008 Source: NASA California Wild Fires 2008  Around 3000 Individual Fires  Most of The Fires Were Triggered By Lightning  Burned Area Around 4686 km 2

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

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

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

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

Urban and Biomass Aerosol They are fundamentally different!

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

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

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

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 coefficients less than unity are not necessarily due to measurement precision and accuracy limitations. Summary

Thank for your Attention! Å = 1 ???