27.aersol.fate.impacts.10

27.aersol.fate.impacts.10 - Fate and Impacts of Atmospheric...

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Fate and Impacts of Atmospheric Aerosols Introduction (a brief review) Fates o Aging & Transformation o Removal o Transport Effects o Air quality / visibility o Climate o Health o Ecosystems
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An aerosol is a relatively stable suspensions of fine solid or liquid particle in a gas . Commonly refer to the particulate component only) Aerosol = Particles = Particulate Matter (PM) PM 2.5 , PM 10 ? A Brief Review Aerosol Properties: Concentration Composition Size Microphysics Shape Phases Impacts: visibility health climate ecosystems
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2. Nucleation 3. Aq-phase rxn Secondary Aerosol 4. PM-phase rxn Primary Aerosol PM Particle EMISSIONS Atmospheric Aerosol Sources Gaseous EMISSIONS Gases (SO 2 , NH 3 , NO x , VOCs …) Low vap. Pres. condensable species Gas-phase oxidation 1. Gas-Particle Partitioning (condensation) PM
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Aerosols (PM) Atmospheric Aerosol Fates Droplet formation Dry Wet , Deposition Chemical Transformations Aqueous Photochemical Heterogeneous Physical Transformations Condensation Evaporation Coagulation 3. Dispersion/ Transport 2. Removal 1. Ageing / Evolution
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Chemical and physical processes Condensation (G P) i.e., Formation of secondary materials Coagulation (P + P P) i.e., Formation of a single particle via collision and sticking of two smaller particles (e.g., Brownian coagulation) Evaporation (P G) • Chemical reactions (A p B P / B g ) In aqueous & particulate phases Aerosol Aging and Evolutions
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• Knudsen number: Kn = 2 λ /D p – Mean free path: the average distance traveled by a molecule btw collisions with other molecules. D p – Particle diameter From Seinfeld and Pandis ≈ 1) Condensation & coagulation are mass transfer processes. Both are function of K n , which defines the nature of the suspending particle relative to the fluid it resides in . air ≈ 65 nm Mass Transfer Processes: Basis a) The continuum regime: << D p (ambient, D p > 0.2 μ m). The gas behave as to the particle as a continuous fluid. a) The free molecular (kinetic regime): >> D p (ambient, D p < 0.01 μ m). The particle is small enough that looks like another gas molecule. a) The transition regime: ≈ D p (ambient, 0.01 < D p < 0.2 μ m). Regimes of gas-particle interactions:
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J c : the total flow of A (g) (moles time -1 ) toward the particle in continuum regime J k : the total flow of A (g) (moles time -1 ) toward the particle in free molecular (kinetic regime) Condensation: Mass Transfer of Gas Molecules to Particles ) ( 4 s g p c c c D R J - = π R p : Particle radius D g : Diffusivity of gas A : Conc. of A far from the particle c s : Vapor phase conc. of A at the particle surface c ); ( 2 s A p k c c c R J - = α 2 / 1 8 = A A m kT c : Mean speed of the molecules : Molecular accommodation coefficient, i.e., probability of A to stick on particle.
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This note was uploaded on 06/29/2011 for the course GENETICS 101 taught by Professor Debrakimbrell during the Summer '09 term at UC Davis.

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27.aersol.fate.impacts.10 - Fate and Impacts of Atmospheric...

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