UCLA AOS145 Jan19

UCLA AOS145 Jan19 - – formation process no ΔT = = ∞...

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=Ng v h radius R p containing n water molecules (via random collision) in the box – homogeneous nucleation. Jan 19 Ideal Gas Law pV=nRT p[Pa] V[m 3 ] n[moles] = . R 8 314Jmol K T[K] Clausius-Clapeyron Equation – relationship between water vapor pressure and temperature , = dlnpH2O satdT ΔHVRT2 Raoult’s Law – Saturation vapor pressure over a flat surface of a solution Assuming solute is in low concentration , = , pH2O satsol XH2OpH2O sat Equilibrium Vapor Pressure over Curved Surfaces – The Kelvin Effect Surface tension ( ) σ surface free energy - Work required to create a unit area of vapor liquid interface ( ): Tension on a film soap bubble ( Gibbs Free energy change for the Formation of a droplet See pdf for ) lecture 5 = - + + - ∆G N ngV ngL 4πRp2σ NgV = nvL 43πRp3 = - + ∆G 4πRp33vLgL gV 4πRp2σ Latent heat released by condensation is absorbed in the surface
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Unformatted text preview: – formation process no ΔT =-( )+ = ∞ ∆G 4πRp33vLln S 4πRp2σ S ppsat < ; ; > ; ~ S 1 subsaturated ΔG 0 ΔG R p ; droplet cannot grow > ; ; S 1 supersaturated for a critical R p , < ; ΔG 0 droplet grows R p * = , critical radius size of droplet at equilibrium – Significant point clouds can only grow if aerosols with R p > R p * are in ! atmosphere Determining R p *: ∂ ∂ = Set ∆G Rp 0 *= ( )= ( ) Rp 2σvLkTln S 2σMRTρLln S A higher the atmospheric saturation will reduce the necessary R p * Kelvin Equation ( ), In a curved surface situation water droplet molecules are packed less , -. densly and have less intra attraction than the flat surface case . Molecules then have an easier time escaping a curved surface...
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UCLA AOS145 Jan19 - – formation process no ΔT = = ∞...

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