Introduction to SCREEN3 smokestacks image from Univ. of Waterloo Environmental Sciences Marti Blad.
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Transcript of Introduction to SCREEN3 smokestacks image from Univ. of Waterloo Environmental Sciences Marti Blad.
Introduction to SCREEN3
smokestacks image from Univ. of Waterloo Environmental Sciences
Marti Blad
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Historically
Image from collection of Pittsburgh Photographic Library, Carnegie Library of Pittsburgh
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C(x,y,z) Downwind at (x,y,z) ?C(x,y,z) Downwind at (x,y,z) ?
Gaussian Dispersion
Dh
hH
z
x
y
¤ Dh = plume rise
h = stack height
H = effective stack heightH = h + Dh
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SCREEN3 Model Assumptions Continuous pollutant emissions Conservation of mass in atmosphere Steady-state meteorological conditions Concentration profiles are represented by
Gaussian distribution—bell curve shape
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SCREEN3 designed for… Single source, short-term calculations
Estimate maximum ground level concentrations
Distance to max. concentration from source Concentrations at user defined distances Simple downwash algorithm
Max. concentrations in near & far wake Estimate concentrations in cavity
recirculation zone Source types
All options for point & flare
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SCREEN3 designed for…(cont.) Full range of meteorological conditions accepted
Stability classes Wind speeds Inversion break up Shoreline fumigation
Determine plume rise for flare releases Includes effects of BID
Buoyancy induced dispersion Simple area & volume sources
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Source Options
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Dispersion Model Structure
INPUT DATA: Operator experience
METEROLOGY EMISSIONS RECEPTORS
Model Output: Estimates of Concentrations at Receptors
Model does calculations
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Model Input Considerations Source type
Point, area, volume, flare Stack or source emission data
Pollutant emission data Stack- or source-specific data Temperature in stack Velocity out of stack
Receptor data
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Input screen 1
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Input Considerations
Actual pattern of dispersion depends on atmospheric conditions prevailing during release
Major meteorological factors that influence dispersion of pollutants Atmospheric stability (& temperature) Mixing height Wind speed & direction
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Meteorological inputs Appropriate meteorological
conditions Appropriate for location Appropriate for averaging time period Wind stability and speed
Flat terrain or complex terrain Distances to points of interest
Receptors
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Input screen: met data
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Discrete Distance input
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Automated Distances input
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Building downwash option
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Run: screen update
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View text results: editor
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Model results: graphs
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Evaluate graph
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Shape of picture
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Review Dispersion = expand & diffuse
Picture
Gaussian = even spreading directions Highest along axis
Input data quality critical Screen3 limitation for reactive chemicals
No reactions assumed to create or destroy
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SCREEN3DEMONSTRATION
Software provided courtesy of
a division of Lakes Environmental Consultants Inc.