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Introduction to SCREEN3 smokestacks image from Univ. of Waterloo Environmental Sciences Marti Blad

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

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3 C(x,y,z) Downwind at (x,y,z) ? Gaussian Dispersion hh h H z x y h = plume rise h = stack height H = effective stack height H = h + h

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4 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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5 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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6 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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7 Source Options

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

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9 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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10 Input screen 1

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11 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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12 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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13 Input screen: met data

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14 Discrete Distance input

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15 Automated Distances input

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16 Building downwash option

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17 Run: screen update

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18 View text results: editor

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19 Model results: graphs

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20 Evaluate graph

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21 Shape of picture

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22 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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23 SCREEN3 DEMONSTRATION Software provided courtesy of a division of Lakes Environmental Consultants Inc.

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