# ENV 6146 Atmospheric Dispersion Modeling

Document Sample

```					       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)

SCREEN3 Tutorial             9
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

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 4 posted: 9/25/2013 language: pages: 34