Session 5, Unit 9Modeling in the Presence of Stable Layers

Dispersion under a Stable Layer

Review of ground reflectionReflection by ground and a ceiling One reflection

2

2

2

2

2

2

2

2

2)2(exp

2)(exp

2)(exp

2exp

2

z

zz

yzy HLz

HzHz

yuQC

Dispersion under a Stable Layer

n reflectionsText p. 11-2, Eqn. (11.1) & (11.2)

When n (completely mixed in the vertical direction), the ground level concentration becomes

2

2

21 2

exp)2( yy

mixy

uL

QC

Dispersion under a Stable Layer

FumigationThe above formula applies or

Lf=H+2z

yf= y(stable)+H/8

2

2

21 2

exp)2( yffyf

fy

uL

QC

Dispersion within a Stable Layer

Fanning plume No ceiling reflection [ET=0 in eqn.

(11.1)] Use values under stable conditions.

y> z

Dispersion between Two stable Layers

Plume trapping y should be adjusted to a value greater

than the one determined by the P-G curves.

Reduce number of reflections to only one.Extreme case – if plume fully penetrate the elevated inversion, the ground level concentration is set equal to zero.

Session 5, Unit 10

The ISC3 ModelBPIP

ISCST3 FundamentalsBasic plume equation For a steady-state Gaussian plume, the

hourly concentration at downwind distance x and crosswind distance y is:

Q – Pollutant emission rateK – Conversion factorD – Decay term

2

21exp

2 yzys

yuQKVD

ISCST3 FundamentalsV – Vertical term including: Effective stack heightStack tip downwash Factors that influence plume rise

Vertical dispersion, including ground and ceiling reflections

Terrain elevation and receptor height Deposition and depletion

ISCST3 Fundamentalsy, z – Dispersion coefficients Determined generally by the methods

described in previous sessions Adjusted for Building wake effects

Huber-Snyder downwash method Schulman-Scire downwash method

Buoyancy induced dispersion

ISCST3 Fundamentalsus – Wind speed at stack height Adjusted using the power law

ISCST3 FundamentalsBuilding wake effects Wake effect boundary Lb = Lesser of building height and

projected widthBoundary:

2Lb upwind 5Lb downwind 0.5Lb on each side

ISCST3 FundamentalsBuilding wake effects Huber-Snyder ProceduresCalculate plume rise due to momentum

alone at a distance of 2hb For unstable conditions:

For stable conditions:

31

22

3

u

xFh

j

m

31

2

/sin(3

suusx

Fhj

m

ISCST3 Fundamentals H=hs+h (no stack tip downwash correction) Determine applicability of Huber-Snyder procedures

Not applicable if: H>2.5hb, or H>hb+1.5hw

Otherwise applicable Huber-Snyder method – Modify y and z

If H<1.2hb, modify both y and z If 1.2hb<H<2.5hb, modify z only Detailed calculations for modifying y and z are on Text

p.14-14 thru 14-16 The method cannot address cavity issues (cavity is

assumed to be in existence within 3hw for tall buildings or 3hb for squat buildings)

ISCST3 Fundamentals Schulman-Scire ProceduresApplicable when hs<hb+0.5LB

The method adjusts z’ by decay factor A: z’’ =A z’ Calculation of A:

A=1, if hehb A=(hb-he)/2LB+1.0, if hb<he hb+2LB A=0.0, if he> hb+2LB

ISC3 General FeaturesMultiple sources in any of four categories (point, volume, area, and open pit)Sources can be grouped in a single runVariable emission ratesCartesian or polar grids and multiple grids in a single runRural or urban optionsPlume riseBuilding downwash; but no cavityStack tip downwash

ISC3 General FeaturesDepositions (dry and wet) and depletionsBuoyancy-induced dispersionWind speed adjustmentVarious averaging timeAll terrainCalm-windOne command regulatory default optionsPollutant decayISCST3, ISCLT3, and ISCEV

Using ISCST3Two common input files: Run stream files Met data input files

Run stream files5 Sections Model options – CO Pathway Source inputs – SO Pathway Receptor network – RE Pathway Met data input – ME Pathway Output options – OU Pathway

Using ISCST3Run stream files – CO example

CO STARTING TITLEONE A Simple Example Problem for the ISCST Model MODELOPT DFAULT RURAL CONC AVERTIME 3 24 PERIOD POLLUTID SO2 RUNORNOT RUN EVENTFIL EVENTEXP.INP ERRORFIL ERRORS.OUT CO FINISHED

Using ISCST3Run stream files – SO exampleSO STARTING

LOCATION STACK1 POINT 0.0 0.0 0.0 ** Point Source QS HS TS VS DS ** Parameters: ---- ---- ---- ---- --- SRCPARAM STACK1 1.00 35.0 432. 11.7 2.4

BUILDHGT STACK1 36*34. BUILDWID STACK1 35.43 36.45 36.37 35.18 32.92 29.66 25.50 20.56 STACK1 15.00 20.56 25.50 29.66 32.92 35.18 36.37 36.45 STACK1 35.43 33.33 35.43 36.45 0.00 35.18 32.92 29.66 STACK1 25.50 20.56 15.00 20.56 25.50 29.66 32.92 35.18 STACK1 36.37 36.45 35.43 33.33

SRCGROUP ALL SO FINISHED

Using ISCST3Run stream files – RE example

RE STARTING GRIDPOLR POL1 STA POL1 ORIG 0.0 0.0 POL1 DIST 100. 200. 300. 500. 1000. POL1 GDIR 36 10. 10. POL1 END RE FINISHED

Using ISCST3Run stream files – ME exampleME STARTING

INPUTFIL PREPIT.ASC ANEMHGHT 20 FEET SURFDATA 94823 1964 PITTSBURGH UAIRDATA 94823 1964 PITTSBURGH DAYRANGE 1-10 ME FINISHED

Using ISCST3Run stream files – OU example

OU STARTING RECTABLE ALLAVE FIRST-SECOND MAXTABLE ALLAVE 50 MAXIFILE 3 ALL 30.0 MAXIALL.FIL 25 MAXIFILE 24 ALL 10.0 MAXIALL.FIL 25** The following card was changed to use the PLOT format instead of UNFORM. POSTFILE 24 ALL PLOT PSTALL.FIL 21 POSTFILE PERIOD ALL PLOT PSTANALL.FIL 22** Note that the following two input cards generate PLOTFILEs with the file** unit dynamically allocated by the ISCST program. When porting the model** to another computer system, the user may need to specify the file units** as is done on the previous four input cards. PLOTFILE 3 ALL 2ND PLT03ALL.FIL PLOTFILE 24 ALL 2ND PLT24ALL.FILOU FINISHED

Using ISCST3Met files – Example (ASCII format)

94823 64 94823 6464 1 1 1 251.0000 3.0866 268.1 5 517.2 455.064 1 1 2 268.0000 5.1444 268.7 4 505.9 505.964 1 1 3 274.0000 5.1444 269.3 4 494.6 494.6…64 1 121 90.0000 10.2888 273.7 4 438.8 438.864 1 122 92.0000 6.1733 272.0 4 456.0 456.064 1 123 80.0000 8.2310 272.0 4 473.1 473.164 1 124 80.0000 7.2022 272.0 4 490.2 490.264 1 2 1 66.0000 7.2022 270.4 4 507.2 507.264 1 2 2 62.0000 6.6877 269.8 4 524.3 524.3…

Using ISCST3Running ISCST3 Prepare input files

Run stream file – Use WordPad, Notepad, or other text editor to create and edit file Select modeling parameters for each sections (CO, SO, RE,

ME, and OU) For each source

Digitize stack locations (x,y,z) Provide stack parameters (emission rate, stack height,

stack temperature, exit velocity, and stack diameter) Digitize buildings, perform building downwash analysis

using BPIP (discussed later), and cut the results from BPIP output and paste them into the SO section

Using ISCST3 Digitize receptors

Receptor grids – range and spacing (coarse grid, medium grid, fine grid, tight grid, property line receptors, discrete receptors)

Place a receptor at each node of grids For each receptor, digitize x, y, and z Consider digital terrain data

Met data file From agencies Unprocessed data vs. model ready data ASCII vs. binary files

Using ISCST3 Executable: ISCST3.EXE Run from DOS

C:\>ISCST3 input.dat output.lst Review results in the output list file Post processing Commercial software packagesBreeze - Trinity ConsultantsBeeline Lakes

BPIPBPIP – Building Profile Input ProgramUsed to generate building profile data to be included into ISC3 for building downwash analysisFor each stack, BPIP determines influencing nearby buildings and calculate GEPFor each stack, BPIP calculates building heights and projected widths of influencing buildings based on 36 wind directions. The output is used in ISC3 for downwash analysis.

BPIPBPIP input - Example

'BPIP users guide test case #1 - input file with 1 bldg and 4 stacks.''ST''METERS' 1.00'UTMN', 210.1'L-Shape' 1 13.006 26 -10. -20. -10. 80. 40. 80. 40. 30. 90. 30. 90. -20.2'Stk100' 11.00 25.00 -10.00 -20.00'Stk101' 12.00 25.00 164.00 159.00

BPIPBPIP primary output – Example

… SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDHGT Stk100 26.00 26.00 26.00 26.00 26.00 26.00 SO BUILDWID Stk100 111.07 107.16 100.00 115.85 128.17 136.60 SO BUILDWID Stk100 140.88 140.88 136.60 128.17 115.85 100.00 SO BUILDWID Stk100 107.16 111.07 111.60 108.74 108.74 111.60 SO BUILDWID Stk100 111.07 107.16 100.00 115.85 128.17 136.60 SO BUILDWID Stk100 140.88 140.88 136.60 128.17 115.85 100.00 SO BUILDWID Stk100 107.16 111.07 111.60 108.74 108.74 111.60…

BPIPBPIP summary output GEP resultsRunning BPIP Running on DOS

C:\>BPIP input.dat output.dat sum.lst

Midterm Review Questions