Lecture 31 - Atmospheric Transport Lecture#31 Reading: M:...

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Unformatted text preview: Atmospheric Transport Lecture#31 Reading: M: Ch. 7 (pg. 392-418) What you should have learned: Air Transport List common steps of an exposure/hazard assessment. What is the concept of an adiabatic lapse rate? What is the relationship between smokestack plume shapes and atmospheric stability? How is the gaussian plume equation derived? What are its inherent assumptions? How are dispersion coefficients calculated for the gaussian plume equation? Why do we need to consider windspeed at the stack height instead of ground level? How can the location of maximum concentration for a pollution point source be estimated? Conducting a Risk Assessment Consider mobile sources (e.g., automobiles) Consider stationary sources (e.g., electrical power plants, buildings) Need emission rates (emission factors) Transport models (CMFR, PFR and gaussian plume models) Risk assessment (CDIxPF) - can look here at maximally exposed individual (MEI) for worst case Evaluations made at each step to determine if given activity (e.g., automobiles or industrial discharge) is acceptable if not, more stringent standards or deny permit for discharge Stationary Sources Pollutant emission plume shape Gaussian Plume Model x y x y x z x z Adiabatic Lapse Rates Since PV = nRT, rising air cools by 10 deg. C per km. atmosphere Atmosphere Concept of Atmospheric Stability Superadiabatic More Dispersion Subadiabatic Less Dispersion Smokestack Plumes Neutrally Stable Air : Vertical and horizontal dispersion Unstable Air : Lots of dispersion Smokestack Plumes Highly Stable Air : Rising air will sink. Sinking air will rise. Not much dispersion. Stable Air Cap ABOVE Stack : Downward only. Mixing depth height max. Mixing Depth Smokestack Plumes Stable air cap BELOW stack height : Lots of dispersion upward Far transport of pollution possible Stable Air Below Stack Stack Gas Rises Stability Line Subsidence Inversion Typical for summer under the influence of high pressure, this lowers relative humidity and provides clear days that can warm the surface significantly with sunlight (LA). surface air rises mid-level air sinks Mixing Depth Radiation Inversion Typical for a winter evening, ground cools faster than atmosphere Inversions tend to create air pollution problems by capping pollution Toward an Air Pollution Dispersion Model Statistical treatment seems plausible! Even if looping, most particles on centerline Plume travel is determined by wind direction & speed....
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This note was uploaded on 04/17/2008 for the course CEE 260 taught by Professor Kimf.hayes during the Fall '06 term at University of Michigan.

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Lecture 31 - Atmospheric Transport Lecture#31 Reading: M:...

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