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.