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1Lecture Ch. 5b• Chapter 5, Problem 3 homework– Kelvin effect– Raoult effect• Aerosol particles– CCN– Indirect effectCurry and Webster, Ch. 5 (skip 5.6, 5.7)For Thursday: Read Ch. 5For Exam: Homework Problem 7, p. 158 (7d misprint)Chemical and Surface EffectsKelvin effectRaoult effectSimplified Köhler EquationKelvin effectRaoult effectKelvin effectRaoult effectMaximum dS/dr=0Critical Radius andSupersaturation€ S(r) = 1+ar−br3dSdr= −ar2+3br4@S*,r* :dSdr= 0 = −ar *2+3br *4ar *2= 3br* =3baS* =1+ar *−br *3= 1+a33b−a327b= 1+4a327b2Aerosol-Cloud Interactions• Activation: Köhler 1921 (Aitken)• CCN/Droplets: Twomey 1959 (Conover)• Particle Growth: Hoppel 1986 (Frick)• Precipitation Suppression: Albrecht 1989 (Rosenfeld,Ackerman, Ramanathan)Cloud Condensation Nuclei(CCN)• cloud condensation nuclei - those particleswhich have large enough radii and enoughsolute content to activate to particles at aprescribed supersaturation• in marine air, only 50% of all aerosolparticles may be CCN for typical clouds,with supersaturations ~ 0.05%-0.5%7.1What is an Aerosol?• Suspension of liquidor solid particles in avapor phase• Colloidal suspensionthat may be stable for<1 s or > 1 yr1.1Particle + Vapor = AEROSOLParticle Sources• combustion• incineration• road dust• power plants• automobiles• sea salt• biogenic• volcanoes1.1Size Range for Particle Sources1.10.002 µm to 0.05 µmviruses0.01 µm to 1 µmtobacco smoke0.2 µm to 10+ µmbacteria0.01 µm to 1 µmautomotive emissionsSize RangeParticle Type3Classification of Pollutants• Fine Particles– less than 2.5 µmin diameter• Coarse Particles– greater than 2.5µm in diameterParticle Types and Sizes0.0001 0.001 0.01 0.1 1 10Particle size (microns)BacteriaBlack Carbon (Soot)Tobacco SmokeVirusesGas MoleculesFine and Coarse Modes010203040 Number (dN/dlogDp), cm-3x1030.01 0.1 1 10Diameter (micrometers)010203040Volume(dV/dlogDp), µm3/cm3Nucleation ModeAitken ModeCondensation Submode DropletSubmodeCoarse ModeUltrafine ParticlesFine Particles Coarse ParticlesAccumulation ModeNumber Distributions vs.Population Distributions1.2Age0 60PopulationDp (µm)0.01 10dNdlogDpAerosol ParticleSize Distribution(Manhattan)Human PopulationAge Distribution(Manhattan)20 400.1 1Particle Size Distributions1.2• Number concentration– Total number N– Differential number n• Mean size– Geometric– Arithmetic– Number-based– Mass-based• Size variability– Standard deviation σ– Geometric standarddeviation σgDpg0.01 10Dp (µm)dNdlogDp∼ σgn(Dp)0.1 1Particle Characteristics• Concentration and size• Chemical composition• Light scatteringDp (µm)0.010.10dndlogDpDpg∼ σgn(Dp)• Regionalvariations inaerosolmass andcomposition[NARSTO,2002]Toronto (1997-99)Egbert (1994-99)Abbotsford (1994-95)Quaker City OH (1999)Arendstville PA (1999)Atlanta (1999)Yorkville (1999)Mexico City - Pedregal (1997)Los Angeles (1995-96)Fresno (1988-89)Kern Wildlife Refuge (1988-89)SulfateNitrateAmmoniumBlack carbonOrganic carbonSoilOther12.3 ug m-38.9 ug m-37.8 ug m-312.4 ug m-310.4 ug m-319.2 ug m-314.7 ug m-355.4 ug m-330.3 ug m-323.3 ug m-339.2 ug m-3Washington DC (1996-99)14.5 ug m-3Colorado Plateau (1996-99)3.0 ug m-3 Mexico City - Netzahualcoyotl (1997)24.6 ug m-3Esther (1995-99)St. Andrews (1994-97)5.3 ug m-34.6 ug m-34Size Characterization of Particles• clusters of molecules• starting at 100molecules/cluster• growth bycondensation ofmolecules is nearlycontinuous• multiple ways to graphsame distribution2468103246810424681052Concentration (cm-3)2 3 4 5 612 3 4 5 6102Diameter (µm) ni Ni Lognormal ni dN/dlogDp dN/dDp ScaledNiParticle SizesDp (µm)0.01 0.10fine modecoarse modeAitken nuclei1.0 10.0 100.0• range of particle sizes isapproximately from 1nm to 1 mm in diameter• range of approximately6 orders of magnitude• concentrations at each ofthese sizes also varySize Distribution ModesDp (µm)0.010.10dndlogDpfine modeaccumulation modenucleation modecoarse modeAitken nucleiprecipitation-sized dropletscloud droplets1.0 10.0 100.0recently nucleated particles• modes of aerosol aredistinguished by– size– sources– behaviorLog-Normal NumberDistributions• DifferentialDp (µm)0.01 0.10Cumulative Distribution (% less than Dp)DpgσgCumulative Number10005084.1%15.9%}Cumulative SurfaceCumulative VolumeDp (µm)0.01 0.10dndlogDpDpg∼ σgn(Dp)• CumulativeMicrophysics• Aerosol includes both particles and vapor• Number, area, volume, mass vary nonlinearly• Deposition velocity depends on size (nano, micro, milli)• Scavenging, coalescence, activation and condensation change the sizedistributionCloud Condensation NucleiActivationActivationCloud ProcessingEvaporationEvaporation0.110Diameter (µm)0.110Diameter (µm)dNdlogDDiameter (µm)0.1105Hoppel Minimum• Particle evolution inremote marineconditions• cloud processing –growth of particlesdue to coalescenceand solutecondensation incloud7.1Seinfeld and Pandis, Fig. 15.23 (Hoppel et al., 1990)Coakley et al., Science, 1987“Ship Tracks”How do Aerosols cool?Aerosol indirect effectscause cooling by cloudsthat reflect more light(e.g. tracks).Aerosol direct effectscause cooling byreflecting more light(e.g. smog).morereflectionmorereflectionclear “smoggy”“normal” “whiter”“City Tracks”Yellow indicates polluted clouds>>Polluted clouds cause coolingRosenfeld, Science, 2000Turkey Manitoba, CanadaSouth AustraliaGlobal Aerosol DistributionCapaldo et al., Nature,


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