1!ROAST 2011!A. The climate penalty for clean fossil fuel combustion"W.#Junkermann, B.#Vogel, and M.#A.#Sutton"Atmos. Chem. Phys. Discuss.,#11,#24567-24589,#2011!B. Climatic effects of 1950–2050 changes in US anthropogenic aerosols – Part 1: Aerosol trends and radiative forcing"E.#M.#Leibensperger, L.#J.#Mickley, D.#J.#Jacob, W.-T.#Chen, J.#H.#Seinfeld, A.#Nenes, P.#J.#Adams, D.#G.#Streets, N.#Kumar, and D.#Rind"Atmos. Chem. Phys. Discuss.,#11,#24085-24125,#2011!C. Earth's energy imbalance and implications"J.#Hansen, M.#Sato, P.#Kharecha, and K.#von#Schuckmann"Atmos. Chem. Phys. Discuss.,#11,#27031-27105,#2011!D. A simple relationship between cloud drop number concentration and precursor aerosol concentration for the regions of earth's large marine stratocumulus decks"D.#A.#Hegg, D.#S.#Covert, H.#H.#Jonsson, and R.#K.#Woods"Atmos. Chem. Phys. Discuss.,#11,#28663-28687,#2011!E. Indirect radiative forcing of aerosols via water vapor above non-precipitating maritime cumulus clouds"M.#A.#Pfeffer, J.#E.#Kristjansson, F.#Stordal, T.#Berntsen, and J.#Fast"Atmos. Chem. Phys. Discuss.,#11,#27637-27659,#2011"http://www.atmos-chem-phys-discuss.net/papers_in_open_discussion.html!Lecture Ch. 5a!• Surface tension (Kelvin effect)!– Hygroscopic growth (subsaturated humidity)!– Saturation!• Chemical potential (Raoult effect)!• Nucleation!– Competition between surface and chemical effects!– Köhler curves!• Aerosol-cloud interactions!Curry and Webster, Ch. 5 (skip 5.6, 5.7); also 4.5.1!Optional: Pruppacher and Klett, Ch. 6!For Monday: Homework Problem 3 and 7 (Ch. 5) {7d misprint!}!Macro-Thermodynamics!• Hot air rises!• Rising air cools!• Cooled moist air saturates!• (Sub & Super)-saturated water vapor condenses!• Condensation liberates heat!Water Saturation!• Saturation concentration of water over a flat water surface !Seinfeld and Pandis, Fig. 15.1 N.B. Equilibrium is in but is NOT the same as “steady state.”!2!Micro-Thermodynamics!• Saturation has the most possible dissolved species!• Equilibrium means two phases are balanced!• Supersaturated states are not stable!• Nucleation initiates a change of “phase” (from particle to droplet)!Bohren, 1987!Wikipedia, surface tension 10/20/09.!Surface Thermodynamics!• Surfaces require energy to form !• Smaller particles have !– higher surface-to-volume ratios!– higher curvature!• Higher curvature requires more energy per mass!€ Sv,w≡ea,wesat,w= exp4 Mwσw / aRTρwDp⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ Hygroscopic Growth of Particles!• Normalized diameter change (growth factor) of sulfate species !– Relative to particle size at 0% RH!Seinfeld and Pandis, Fig. 9.3 Free Energy Equation!• Surface energy!• Free energy at constant T, P!3!Kelvin Equation!• vapor pressure over a curved interface always exceeds that of the same substance over a flat surface!– vapor pressure of a liquid = energy necessary to separate a molecule from the attractive force of its neighbors!– curvature - increases the distance between a molecule and its neighbors so it has fewer neighbors -- therefore it is easier for molecules to break free!• for pure water Kelvin effects are important <0.05 µm diameter droplets!4.1 ⎥⎥⎦⎤⎢⎢⎣⎡==pwwwwwsatwwDRTMxPPRHρσγ4expParticle composition xw mole fraction of water γw activity coefficient for water σw surface tension of solution ρw density of aqueous solution Mw molecular weight Dp particle diameter Ambient conditions RH relative humidity T temperature Pw vapor pressure Pwsat saturation pressure Raoult’s "Law!Raoult’s "Law!Chemical Potential!• From Maxwell’s equations!• Integrating from vapor to liquid!Measured Hygroscopic Growth!• Particle balance for levitating particles (Tang et al., 1987)!• Growth compensated by change in electric field!• Deliquescence occurs at transition from dry to wet!Seinfeld and Pandis, Fig. 9.74!Condensed Water Molecules!• Change in number of liquid molecules!Critical Radius and Supersaturation!• Integrate then find maximum!Lecture Ch. 5b!• Chapter 5, Problem 3 homework!– Kelvin effect!– Raoult effect!• Aerosol particles !– CCN!– Indirect effect!Curry and Webster, Ch. 5 (skip 5.6, 5.7); also 4.5.1!Today/Tomorrow: Homework Ch. 5 due!Wednesday: Read Ch. 6 + current research (either Bahadur or Roberts).!• Liquid (H2O/EtOH) supersaturated with vapor (CO2) nucleates on salt to form bubbles Bubbles • Vapor (air) supersaturated with liquid (H2O) nucleates on particles to form droplets Clouds5!Chemical and Surface Effects!Kelvin effect!Raoult effect!Raoult effect!Both Kelvin and !Raoult effects!Simplified Köhler Equation!Kelvin effect!Raoult effect!Kelvin effect!Raoult effect!Maximum dS/dr=0!Critical Radius and Supersaturation!€ 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 +4a327bCloud Droplet Nucleation!• particle activation - process by which droplets (several micron in size) are formed (or activated) from primarily submicron particles; also called heterogeneous nucleation or just nucleation by cloud physicists!– process illustrates the conditions required for growth to droplets!– the approach used assumes that this formation is an equilibrium process!6!Köhler Curves!• Köhler curves for sodium chloride and ammonium sulfate !– Dry diameters 0.05, 0.1, 0.5 µm!– Supersaturation of 1% is equivalent to 101% relative humidity!Seinfeld and Pandis, Fig. 15.5 Kelvin effect!Raoult effect!Activation on Particles!• Soluble salts dissolve! Sv,w= exp2Mwσs /aRTρwa−υΦsmsMw/ Ms4πa33⎛ ⎝ ⎜ ⎞ ⎠ ρs"− ms⎛ ⎝ ⎜ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎟ Kelvin effect! Raoult effect!Activation of CCN to Droplets!• Variation of the equilibrium vapor pressure of an aqueous solution drop containing ammonium sulfate and insoluble material !– Initial dry particle diameter 0.1 µm !– Soluble mass fractions 0.2, 0.4, 0.6, 1.0 at 293K!7.1 Seinfeld and Pandis, Fig. 15.8 Aerosol-Cloud Interactions!• Activation: Köhler 1921 (Aitken)!• CCN/Droplets: Twomey 1959 (Conover)!• Particle Growth: Hoppel 1986 (Frick)!•
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