PowerPoint Presentation

Absorption by ambient aerosols during CalNexChris Cappa (UCD) Paola MassoliTim OnaschDoug WorsnopKatheryn KolesarJani HakalaShao-Meng Li Ibraheem NuaamanKathy Hayden Trish QuinnTim BatesDan Mellon and moreCaLNexAtntisl

1Aerosol Volatility and Optical Properties

[Lack and Cappa, ACP, 2010]Light absorption by particles from black carbon (soot) and brown carbon

Coatings on BC can theoretically enhance absorption in climatically important ways [e.g. Jacobson, Nature, 2001]

Enhancement factor can be calculated from Mie theory, but limited validation from ambient measurements

Objective: to directly measure the absorption enhancement factor for ambient particles at multiple wavelengths2AmbientReally hotLarge EnhancementSmall EnhancementHighly ScatteringLess ScatteringBrown CarbonNo Brown CarbonAbsorption by brown carbon should contribute more to total absorption at short lApproach: Heat Particles to Drive Off Coatings3

4MeasurementsThermo-denuderHR-ToF-AMSSP-AMSPAS/CRDSMPSSP2MASTorNote: PM1 cutoffNon-refractory particle compositionBC & coating compositionParticle absorption & extinctionSize DistributionBC mass distributionEnv. CaAerodyneUC DavisEnv. CaEnv. CaPAS/CRD measures light absorption and light extinction at 532 nm and 405 nmSP-AMS measures BC mass and coating compositionSP2 measures BC mass and infers coating thicknessSP2 and SPAMS tell us something about how coating thickness has changed upon heatingSP2 BC measurement can tell us about particle losses through the TD5

Particle Transmission CorrectionSimilar results to Huffman et al. (2008): Tr = 0.98 0.00082*Temp6

Influence of heating on particle extinction (532 nm)Black = ambientRed = denuded7

Influence of heating on particle extinction

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Lines are binned data over different time periods

Total aerosol volatility varies greatly with time/location

Very similar results from SMPSInfluence of heating on particle extinctionStart of CampaignEnd of Campaign9

Influence of heating on particle absorption

Note: only include periods when babs,ambient > 0.5 Mm-1

532 nm405 nm10

Influence of heating on particle absorption

532 nm405 nm11

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Theoretical Calculations of Aerosol Optical PropertiesUse core-shell Mie theory to calculate evolution of sabs, sext and SSADp(particle) = 400 nmDp(core) = 80 nmsabs = 9.8 x 10-15 m2/particlesext = 2.9 x 10-13 m2/particleSSA = 0.97Dp(particle) = 100 nmDp(core) = 80 nmsabs = 3.8 x 10-15 m2/particlesext = 4.4 x 10-15 m2/particleSSA = 0.13Dp(particle) = 200 nmDp(core) = 60 nmsabs = 2.9 x 10-15 m2/particlesext = 1.5 x 10-14 m2/particleSSA = 0.81Dp(particle) = 120 nmDp(core) = 60 nmsabs = 2.0 x 10-15 m2/particlesext = 2.8 x 10-15 m2/particleSSA = 0.16Eabs = 2.57FRext = 0.015DSSA = 0.84Eabs = 1.45FRext = 0.19DSSA = 0.6513

Model: Mie Core-ShellDp = 250 nmSSAi = 0.95; Dcore = 50 nm

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Model: Mie Core-ShellDp = 250 nmSSAi = 0.95; Dcore = 50 nmSSAi = 0.88; Dcore = 70 nmSSAi = 0.77; Dcore = 90 nmSSAi = 0.67; Dcore = 110 nm

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Model: Mie Core-ShellSSAi = 0.95SSAi = 0.88SSAi = 0.77SSAi = 0.67; vary DpSSAi = 0.58Dp = 150 nmDp = 100 nmDp = 80 nm

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Mie Core-Shell Results

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Mie Core-Shell Results

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Since we are talking about California anywaysame experiment done at CARES, but with fixed TD temperature (225 C) and PM2.5Note: variation in FRext from atmosphere, not temperature

20Why such an (unexpectedly) low absorption enhancement?1. Concern: particles are not internally mixed2. Particles are internally mixed, but not with core-shell morphology+21

H-TDMA indicates aerosol dominated by single growth mode22

Dp,core = 40 nmDp,core = 140 nmPoints = observedLines = calculations23

SP-AMS sees only particles that contain black carbonSSA shows similar variation with Dp,core = 40 nmDp,core = 140 nmwhich would only be the case if particles are internally mixed.24

Brown Carbon Absorption

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Brown Carbon Absorption~10% of absorption at 405 nm may be due to Brown CarbonImaginary Refractive Index ~ 0.00926ConclusionsAbsorption enhancements much smaller than expectedSuggests internal mixtures but not with core-shell morphologyAbsorption by brown carbon ~ 10% of total at 405 nmThanks again to all my great collaborators, the R/V Atlantis Crew and the EPA and NOAA for funding.

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