Introduction to SCREEN3

Marti Blad

smokestacks image from Univ. of Waterloo Environmental Sciences

Historically

Image from collection of Pittsburgh Photographic Library, Carnegie Library of Pittsburgh

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H h D h z

Gaussian Dispersion

H = h + D h  D h = plume rise h = stack height H = effective stack height x y C(x,y,z) Downwind at (x,y,z) ?

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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 5

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 6

Source Options

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Dispersion Model Structure

INPUT DATA: Operator experience EMISSIONS METEROLOGY RECEPTORS Model does calculations Model Output: Estimates of Concentrations at Receptors 8

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 9

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 11

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 12

Input screen: met data 13

Discrete Distance input 14

Automated Distances input 15

Building downwash option 16

Run: screen update

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View text results: editor 18

Model results: graphs 19

Evaluate graph 20

Shape of picture 21

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 22

SCREEN3

DEMONSTRATION

Software provided courtesy of a division of Lakes Environmental Consultants Inc.

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