ENV 6146 Atmospheric Dispersion Modeling

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ENV 6146 Atmospheric Dispersion Modeling Powered By Docstoc
					       SCREEN 3 TUTORIAL
ENV 6146:Atmospheric Dispersion Modeling
             March, 2010




                     Presented by:
                  Adeeba Abdul Raheem
Web resources to download SCREEN3 and
Modeling Guides:
 A: Software
 EPA (Dos based program):
 Http://www.Epa.Gov/ttn/scram/dispersion_screening.Htm
 User friendly interface:
 Http://www.Weblakes.Com/products/screen/index.Html



 B:Guidance for Air Dispersion Modeling
 http://www.epa.gov/ttn/scram/userg/screen/screen3d.pdf

 http://www.valleyair.org/busind/pto/tox_resources/Mo
 deling%20Guidance%20W_O%20Pic.pdf/

 http://www.colorado.gov/airquality/permits/screen.pdf


 2                 SCREEN3 Tutorial
OUTLINE

Introduction
Overview of SCREEN3
Getting started
Input data
Different interfaces
Model description
Examples
Conclusions


                   SCREEN3 Tutorial   3
INTRODUCTION


SCREEN3 is a steady-state Gaussian plume
 model which uses worst-case meteorological
 data to predict ambient pollutant
 concentrations resulting from single continuous
 emission sources




                SCREEN3 Tutorial         4
INTRODUCTION


SCREEN3 is the current regulatory screening
 model for air permitting applications.

The original SCREEN model was released by EPA
 in 1988

Based on the same steady-state Gaussian plume
 algorithms as ISC3


                SCREEN3 Tutorial        5
OVERVIEW SCREEN 3

SCREEN3 can perform all the single source short-term
calculations including:

Estimating max. ground-level concentrations
Incorporating the effects of building downwash
Estimating concentrations in the cavity
 recirculation zone.
Estimating concentrations due to inversion break-up
 and shoreline fumigation.
Determining plume rise for flare releases.

                  SCREEN3 Tutorial            6
     COMPARISON




http://www.trainex.org/web_courses/subpart_x/Encyclopedia%20X%20pdf%20files/Environmental%20Assessment%20pdf%20files/AirDispersionEmissionModelingX.pdf
Spatial and temporal scales of widely used air quality
models




                                  http://www.epa.gov/ttn/fera/data/risk/vol_1/chapter_09.pdf
GETTING STARTED –SCREEN 3



Convert all lengths and distances to meters
Convert temperatures to degrees Kelvin
Identify building contributions to air dispersion
 (stack emissions)




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INPUT DATA

To perform a modeling study using SCREEN3, data
for the following input requirements must be
supplied:
Source Type (Point, Flare, Area or Volume)
Physical Source and Emissions Characteristics
 Meteorology: SCREEN3 can consider all
  conditions, or a specific stability class and wind
  speed can be provided.
Building Downwash: If this option is used then
  building dimensions (height, length and
  width)must be specified.
                  SCREEN3 Tutorial            10
INPUT DATA(Meteorology options)

Full: complete set of stability - wind speed
 combinations examined for worst case scenario at
 each downwind location

Stability class: worst case scenarios for
 predetermined wind speeds

Stability class - wind speed combination:
 calculations reported for only the combination
 specified by user

                  SCREEN3 Tutorial           11
INPUT DATA(Fumigation Option)
Inversion break-up - pollutant release into the
 radiation inversion layer moves horizontally with
 little dispersion due to the strong stability of the
 inversion layer

Shoreline fumigation (sources within 3000 m of a
 large body of water)

If a source with a tall stack (greater than 65m) is
 located in a coastal region, then the effects of coastal
 (or shoreline) fumigation may be significant
                   SCREEN3 Tutorial             12
Point Source


Point sources are typically used when modeling
releases from sources like stacks and isolated vents.
Input requirements for point sources include:




                   SCREEN3 Tutorial            13
Input Requirements To Run Screen Models For
Point Source


 Emission rate (g/s)
 Stack Height (m)
 Shortest distance to property line
 Stack velocity (or volumetric airflow)
 Stack gas temperature (K)
 Stack Inside Diameter
 Building Height, Length, Width



                   SCREEN3 Tutorial        14
Area Source
Area sources are used to model low level or ground
level releases where releases occur over an area
(e.g., landfills, storage piles, slag dumps, and lagoons).




                     SCREEN3 Tutorial             15
Input Requirements To Run Screen Models
For Area Source


Emission Rate per unit area (g/(s-m2))
Source Release Height
Larger Side Length of Rectangular Area (m)
Smaller Side Length of Rectangular Area (m)
Receptor Height Above Ground (m or ft.): This
 may be used to model impacts at “flagpole”
 receptors. The default value is assumed to be 0.0 m
 (i.e., ground-level receptors)
Wind Direction

                  SCREEN3 Tutorial           16
Volume Source

 Volume source is used to model releases from a
 variety of industrial sources, such as building roof
 monitors, fugitive leaks from an industrial facility,
 multiple vents, and conveyor belts.




                    SCREEN3 Tutorial             17
Input Requirements To Run Screen Models
For volume Source


 Emission Rate in grams per second (g/s).
 Source Release Height above ground surface
 Initial Lateral Dimension(m)
 Initial Vertical Dimension(m)
 Receptor Height Above Ground [m or ft]




                  SCREEN3 Tutorial         18
Input Requirements To Run Screen Models
For volume Source




               SCREEN3 Tutorial      19
Flare Source


 Flare sources are used as control devices for a
 variety of sources. SCREEN3 supports flares directly
 through its flare source type.




                   SCREEN3 Tutorial           20
Input Requirements To Run Screen Models
For Flare Source

Emission Rate in grams per second (g/s).
Flare Stack Height
Total Heat Release Rate in calories per second
 (cal/s) for the flare.
Receptor Height Above Ground
EPA’s SCREEN model assumes
      stack gas exit velocity (Vs) = 20m/s,
      stack gas exit temperature (Ts) of 1,273K
       calculates an effective stack diameter based on the
      heat release rate.

                    SCREEN3 Tutorial                 21
Building Downwash

 Buildings and other structures near a relatively short stack can
  have a substantial effect on plume transport and dispersion, and on
  the resulting ground-level concentrations that are observed.




                         SCREEN3 Tutorial                    22
Building Downwash


Building downwash can occur when
      HStack= HS< Hb + 1.5L
                                      HStack= Height of Stack
                                      Hb = Height of Building
                                      L = lesser of Hb or PBW
                                      PBW = Maximum
                                      Projected Building Width

Screen model will do this calculation when the
 building downwash option is used. If HS> Hb + 1.5L,
 then building downwash will not be shown in
 SCREEN results

                   SCREEN3 Tutorial                     23
Input Requirements To Run Screen Models
For Building Downwash



 Building Height(m)
 Minimum Horizontal Building Dimension(m)
  Maximum Horizontal Building Dimension (m)




                 SCREEN3 Tutorial        24
SCREEN3 NON-REGULATORY OPTIONS

An alternative mixing height algorithm (Brode,
 1991)

Optional input of an anemometer height in
 place of the default height of 10 meters.

An alternative building cavity algorithm
 (Schulman and Scire, 1993)


                SCREEN3 Tutorial            25
BRODE ALGORITHM FOR MIXING HEIGHT


The alternative mixing height is determined by using the
 maximum of a predetermined mixing height or a value
 adjusted slightly higher than the plume height, whichever
 is greater.

Selection of this algorithm results
in concentrations that are generally
more conservative than output
from the ISCST3 model.


                      SCREEN3 Tutorial            26
ANEMOMETER HEIGHT ≠ 10 M

The optional input of an anemometer height in
 place of the default height(10 m) affects the stack
 top wind speeds for Choice of Meteorology
 selections 1 and 2

For Choice of Meteorology selection 3, the user is
 prompted to enter a 10 meter wind speed which is
 unaffected by any optionally entered anemometer
 height

                   SCREEN3 Tutorial          27
SCHULMAN AND SCIRE BUILDING CAVITY ALGORITHM



The published concentration results using this
 algorithm model the sampled wind tunnel test
 concentrations better than the regulatory algorithm
 for the range selected.




                  SCREEN3 Tutorial          28
IMPORTANT INFORMATION:

The complex terrain algorithms in SCREEN3 are for
 point and flare sources, not area/volume sources.

It is usually recommended that the receptor height be
 set to 0 meters (e.g., ground-level)

In simple terrain areas, SCREEN3 calculates 1-hour
 concentration estimates. In complex terrain, the model
 provides 24-hour concentration values.
(Conversion tables will be provided in the class)


                           SCREEN3 Tutorial         29
IMPORTANT INFORMATION:

 Automated Distances Option:
  It gives the user the option of using a preselected array of 50 distances
  ranging from 100 m out to 50,000 m (50 km) using the following
  increments




 Discrete Distances Option:
  The Discrete Distances option allows the user to find the maximum
  impact at specific locations of interest, such as nearby residences,
  hospitals, or schools.


                           SCREEN3 Tutorial                     30
SCREEN3 USER FRIENDLY INTERFACE




            SCREEN3 Tutorial   31
SCREEN3 INTERFACE




          SCREEN3 Tutorial   32
SCREEN3 EXAMPLE




          SCREEN3 Tutorial   33
THANKS?


 SCREEN3 Tutorial   34

				
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