1 Lecture 16 Aerosol Light Scattering and Cloud Nucleation ID: 466813
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1 Atmospheric ChemistryProf. Jose-Luis Jimenez Lecture 16: Aerosol Light Scattering and Cloud Nucleation We study aerosols because of effects on:HealthEcosystems (acid rain)VisibilityClimateTodayAerosol light scatteringAerosol water uptakeSubsaturatedInfluence in light scatteringSupersaturated: cloud formation 2 Harvard six-Mortality fine particle Disputed for a New Dutch k Mechanism still From FP&P Particles can scatter and absorb These effect limit From Jacob 3 radiation intensity (e.g., radiation intensity above atmosphereair massattenuation coefficient due toabsorption by gases (ag)scattering by gases (sg)scattering by particles (sp)absorption by particles (ap) Rayleighscattering Deep UV O, NMid UV & visible ONear IR HInfrared CO From F-P&P & S. Nidkorodov Purely physical process, not Approximation:Strongly increases as Reason why sky From Turco 5 From FP&P MieScattering I 22111208)(),(RiiIRI intensity parametersFunctions of m: refractive index = c/vImaginary part of m From FP&P 8 MieScattering per unit volume A single 10 m particle scatters much more than a 1 m particleBut the reverse is true per unit volume (one 10 m particles) From FP&P From FP&P Scattering in Atmosphere By coincidence, mass concentration is largest for particles that are most efficient scatterersScattering by fine mode dominates total scattering in most conditionsSome exceptions such as dust storms From FP&P 10 Mass Scattering Efficiencies From FP&P Be careful with these as they depend on size dist. & state of mixing Dependence of Scattering on RH From FP&P 11 Why Dependence on RH is so Strong From FP&P / (DRH (%) 1.71.3 CompoundRHC (%)RHD (%)408010402862NaCl4275 Deliquescence and Efflorescence From Don CollinsTexas A&M U 12 Deliquescence for (NH4)2 From FP&P Deliquescence Points From FP&P 14 to cloud droplet formation As the RH approaches and exceeds 100%, the solution droplet becomes increasingly dilute approaches 1.0 and the droplet volume can be directly related to the amount of water. 2/132/133274)1ln(ln30exp432expBASSeeABreedrdrBrArMWmiMWTrReecccssdcssdswwwwssd Radius Pure water1x solute2x solute KöhlerCurve Example: Calculate the critical supersaturation of a 0.08 m diameter ammonium sulfate particle From Seinfeld, J. H., and S. N. Pandis, Atmospheric Chemistry and PhysicsJohn Wiley, New York, 1998. From Don Collins, Texas A&M U. The next set of slides shows the As the air rises in the subsaturatedatmosphere below the cloud, the absolute humidity stays constant, but RH increases as T decreases. The particles eventually deliquesce and keep taking up When the particles enS reaches a point higher than Scritfor the larger particle, which leads to activation S always stays below Scritfor the smaller particle, so that one remains unactivatedthrougoutthe cloud. This is called the interstitial aerosol. TyFinally, if the air containing the particles goes beyond the topof the cloud, both particles lose most water because the air is again This animation was prepared by Don Collins at Texas A&M Univ 15 1400 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) 1.008 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r (m) From Don Collins, Texas A&M U. 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r (m) 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) From Don Collins, Texas A&M U. 17 5 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r (m) 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 1400 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U. 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r (m) 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U. 19 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r ( m ) 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U. 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 m) 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U. 21 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 m) 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U. 6 7 8 9 1RH (fraction) 0.01 0.1 1 10 r (m) 1.006 1.004 1.002 1.000 0.998RH (fraction) 0.01 0.1 1 10 r (m) 1400 1200 1000 800 600 400 200 0Height (meters) 6 7 8 9 1RH (fraction) From Don Collins, Texas A&M U.