ADMS Screen 3

Transcription

ADMS Screen 3

ADMS
Screen 3
USER GUIDE
CERC
ADMS-Screen 3
User Guide
February 2004
CERC Limited
3 Kings Parade
Cambridge
CB2 1SJ
Telephone: (01223) 357773
Facsimile: (01223) 357492
Email: [email protected]
Web site: http://www.cerc.co.uk
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CONTENTS
SECTION ONE: INTRODUCTION ..................................................................................... 5
1.1 About ADMS-Screen 3.............................................................................................. 5
SECTION TWO: GETTING STARTED .............................................................................. 6
2.1 System Requirements................................................................................................. 6
2.2 Installation.................................................................................................................. 6
2.3 Getting around the interface....................................................................................... 7
2.3.1 Mouse buttons.................................................................................................... 7
2.3.2 Keyboard access................................................................................................. 7
SECTION THREE: RUNNING THE MODEL .................................................................... 9
3.1 Input Windows........................................................................................................... 9
3.2 Data Screen Parameters ............................................................................................. 9
3.2.1 Project Name...................................................................................................... 9
3.2.2 Source Data...................................................................................................... 10
3.2.3 Outflow ............................................................................................................ 10
3.2.4 Emissions Data................................................................................................. 10
3.2.5 Source Location ............................................................................................... 11
3.2.6 Building Effects ............................................................................................... 11
3.2.7 Output .............................................................................................................. 11
3.3 Building Definition Window ................................................................................... 12
3.3.1 Building Parameters......................................................................................... 13
3.4 Saving the data and running the model.................................................................... 16
SECTION FOUR: OUTPUT ............................................................................................... 17
4.1 Description of output files ....................................................................................... 17
4.1.1 *.CSV (Short term output)............................................................................... 17
4.1.2 *.SCN (Long term output) ............................................................................... 17
4.1.3 *.GLT (Long term output) ............................................................................... 18
4.1.4 *.MAX (Worst case concentrations)................................................................ 18
4.1.5 *.LOG (Log file).............................................................................................. 18
4.2 Graphical output....................................................................................................... 19
4.2.1 Line plotting facility ........................................................................................ 19
4.2.2 Contour plotting in Excel................................................................................. 20
4.2.3 Contour plotting link to Surfer......................................................................... 23
SECTION FIVE: EXAMPLES ................................................................................... 25
5.1 Simple example stack chimney.SPL ....................................................................... 25
5.2 Stack with building effects build.SPL................................................................... 28
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SECTION SIX: TECHNICAL SUMMARY....................................................................... 29
6.1 Meteorological data ................................................................................................. 27
6.2 Parameterisation of the boundary layer ................................................................... 31
6.2.1 Boundary Layer Structure................................................................................ 31
6.3 Mean concentration calculations.............................................................................. 33
6.3.1 Dispersion Parameters ..................................................................................... 33
6.3.2 The Stable and Neutral Boundary Layer ......................................................... 33
6.3.3 The Convective Boundary Layer ..................................................................... 35
6.4 Plume Rise Module.................................................................................................. 37
6.5 Building Effects Module.......................................................................................... 38
6.5.1 Stack Induced Downwash................................................................................ 39
6.5.2 Limitations of the Buildings Effects Module................................................... 40
6.6
Statistics: Long term average and percentiles................................................. 42
6.7 Calculation of concentrations for comparison with limit values ............................. 43
APPENDIX A: LIMITS AND GUIDELINES ................................................................... 44
APPENDIX B: METEOROLOGICAL DATA .................................................................. 45
APPENDIX C: SURFER TIPS............................................................................................ 49
APPENDIX D: REFERENCES........................................................................................... 55
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Section One: Introduction
SECTION ONE: INTRODUCTION
1.1
About ADMS-Screen 3
ADMS-Screen 3 is a “new generation” dispersion model which models
buoyant and passive releases to atmosphere to give a rapid, or screening,
estimate of ground level concentrations. Its features include:
•
•
•
•
•
Output comparing predicted concentrations with AQS objectives and EU
limits
Modelling of the effect of a single building on dispersion
Line plotting facility
Results in a format suitable for contour plotting in Excel, and a contour
plotting link for users of Surfer
Numerical output giving a rapid impression of the areas of high
concentration
Since the release of ADMS 2 in 1995 as the first practical new generation
model, the debate within the modelling community has progressed and there
is now wide spread agreement that new generation models are the most
appropriate tools for practical dispersion modelling. The new models are
characterised by two main features:
(i)
(ii)
The description of the atmospheric boundary layer, not in terms of Pasquill
Class but in terms of two parameters: the boundary layer depth, h and the
Monin-Obukhov length, LMO.
Dispersion under convective meteorological conditions uses a skewed
Gaussian concentration distribution, shown by validation studies to be a
better representation than a Gaussian expression.
In addition to using this up to date description of the atmospheric boundary
layer, ADMS is the only model of its kind which solves the conservation
equations to model plume rise rather than using empirical relations e.g.
Briggs.
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Section Two: Getting Started
SECTION TWO: GETTING STARTED
2.1
System Requirements
ADMS-Screen 3 has a 32 bit numerical code and a 16 bit interface which
will run in a Windows 98, NT 4, 2000 or XP (Professional) environment.
The minimum recommended machine specification is a Pentium 266MHz
machine with 64MB RAM and 100MB Hard Disk space, although the model
will run at reduced speed on machines of lower specification. Table 2.1
shows typical run times achieved on the minimum specification machine.
Type of run
Run time
No buildings
effects
10 minutes
With building
effects
15 minutes
Table 2.1 Timings of typical ADMS-Screen 3 runs
2.2
Installation
If you have a previous version of ADMS-Screen 3 installed on your
computer, please uninstall it before installing the latest version.
ADMS-Screen 3 is supplied on a CD ROM and comes complete with an
installation program. If your computer runs Windows NT, 2000 or XP, log
on as local administrator before installing. To install, insert the CD into the
CD drive on your computer. The installation program should automatically
start. If it doesn’t, locate the CD drive in Explorer and double-click on the
file setup.exe to begin installation. Follow the instructions shown on the
screen as the installation procedure continues.
A default directory for installation is chosen by the installation program. Use
the Browse... button if you want to install in a different directory which
already exists or type in the name of a new directory you want to create.
A separate licence file is provided on a floppy disk. This file contains the
unique licence number and information for each customer. The file is called
ascreen3.lic and should be placed in the directory in which you have
installed ADMS-Screen 3.
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2.3
Getting around the interface
2.3.1 Mouse buttons
Unless otherwise stated, mouse instructions refer to the left button.
If the mouse options have been used to reverse the mapping (e.g.
because you are left-handed), the right mouse button should be used
instead.
2.3.2 Keyboard access
All mouse instructions in this manual can be reproduced using
keystrokes. A brief guide to these keystrokes is given in Figure 2.2
Moving the cursor between data entry boxes
TAB
Moves the cursor forward through data entry
boxes or buttons
SHIFT + TAB Moves the cursor backwards through data entry
boxes and buttons
Entering data into a box
DELETE
Deletes the character immediately to the
right of the cursor
BACKSPACE
Deletes the character immediately to the left
of the cursor
Å arrow
Moves the cursor one space to the left in the
current box
Æ arrow
Moves the cursor one space to the right in
the current box
SHIFT + arrow
Begins highlighting characters in the
direction of the arrow (see above)
Highlighted text
DELETE
(Type)
Radio buttons
Å arrow
Æ arrow
Deletes all highlighted characters
Typing text replaces the highlighted text with
new text
Moves the cursor up through the radio buttons
for the current item
Moves the cursor down through the radio
buttons for the current item
Figure 2.2 – Keystrokes to enable you to move through the ADMSScreen 3 interface
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Access Keys
Also known as shortcut keys, these are combinations of keys that
perform some of the main commands. For example, menu
commands that have one letter underlined are accessible by typing
ALT and the underlined letter together. For example, the menu
command OPEN may be input by typing ALT + F for FILE and
then ALT + O.
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Section Three: Running the Model
SECTION THREE: RUNNING THE MODEL
3.1
Input Windows
All data are entered via the main Data screen of the interface. Buildings data are
entered from a sub-screen of the Data screen.
3.2
Data Screen Parameters
The Data input window is shown in Figure 3.1. The toolbar may be hidden or
reinstated by selecting Preferences….Toolbar from the File menu.
Figure 3.1 Data input screen
Below is a complete list of the input parameters to be entered.
3.2.1 Project Name
Here a title for the run may be entered. This will be recorded in the log file of
the model run.
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3.2.2 Source Data
The numerical parameters may be integer or real.
(i)
Height of source above ground
The height of the exit point of the source above the local ground level,
for example the height of the top of a chimney.
Minimum
Maximum
= 0 metres
= 2000 metres
(ii)
Internal diameter of source
The internal diameter of the source (used in the plume rise
calculations).
Minimum
= 0 metres
Maximum
= 100 metres
(iii)
Temperature of emission
Temperature of the outflow.
Minimum
= 0°C
Maximum
= 2000°C
3.2.3 Outflow
The user may specify either the volume flow rate or the vertical velocity of
emission and selects one or the other by clicking the radio buttons. Values are
at release temperature and actual pressure, not at 'normal’ temperature and
pressure. The numerical parameters may be integer or real.
(i)
Volume flow rate
The total volume flow rate of the emission (i.e. pollutants and air) in
actual m3/s.
Minimum
= 0 m3/s
Maximum
= 10,000 m3/s
(ii)
Vertical velocity at source
The vertical exit velocity of the emission.
Minimum
= 0 m/s
Maximum
= 100 m/s
If the outflow rate is set to zero, no plume rise calculations will be performed.
3.2.4 Emissions Data
Here the user selects the pollutants for which concentrations will be
calculated. The emission rate in g/s is entered as a real or integer value.
Output will be given for all pollutants with a non-zero emission rate. The
name of the ‘User defined’ pollutant at the bottom of the pollutants table may
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be edited by the user. The other pollutant names cannot be changed by the
user.
The units in which the output will be given are also specified here. The
selected units will only be used for short term output and General long term
output (see Section 3.2.7). The concentration of most of the pollutants can be
given in ng/m3, µg/m3, mg/m3, ppb or ppm. Note, however, that output cannot
be given in ppb or ppm for particulates, NOx, lead or the user-defined
pollutant. Output for comparison with AQS and EU limits is automatically
given in the units in which the limit is expressed.
3.2.5 Source Location
The user selects the meteorological data set used for long term calculations
from a list of regions according to the location of the source, by clicking the
radio buttons. For details of the meteorological data sets, see §6.1.
The surface roughness is the characteristic roughness length of the source
surroundings. Pressing the help button to the left of this box lists suggested
values of surface roughness as a function of land use. Clicking on any of the
values has the effect of selecting that value, or the user may enter his or her
chosen value in the box.
Minimum
= 10-6 metres
Maximum
= 10 metres
3.2.6 Building Effects
The user may consider the effect of a single building on the dispersion. To
select this option, click the check box so that a tick appears and the Define
button becomes black. The Building parameters are entered in the Building
Definition window which appears when the Define button is clicked, see §3.3.
3.2.7 Output
Here the type of output required and the output domain are specified.
Short term
If short term output is selected, concentrations at points downstream of the
source are calculated for a range of meteorological conditions (see §6.1).
Long term
There are three options for long term calculations. If AQS or EU are selected,
concentrations will be calculated for comparison with the UK’s Air Quality
Strategy objectives or EU limits, for each selected pollutant. A full list of the
limits and guidelines considered is given in Appendix 1, and is also accessible
from the drop-down Limits menu in the interface. If General output is
selected, the long term average concentration and up to two user defined
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percentiles will be calculated for each selected pollutant. Any combination of
these three options can be chosen.
Maximum downstream distance
The output domain is defined by entering the maximum downstream distance
from the source, Xmax, in metres. For short term calculations, output is given
at 25 downstream points (i.e. under the plume centreline) at ground level,
equally spaced between the source and Xmax. For long term concentrations,
output is given on a regular Cartesian grid of 21 by 21 points, with the x-axis
aligned from west to east and the y-axis aligned from south to north. The grid
is centred on the source, at ground level, extending a distance Xmax from the
source in each direction.
Minimum
= 10 metres
Maximum
= 105 metres
3.3
Building Definition Window
This window is shown in Figure 3.2. The user should model a building or buildings
as one idealised cuboid. This is a simplified treatment for more than one building,
which could be modelled more completely by another program, such as ADMS 3.
The user is not allowed to enter into the model details of a source-building
configuration with the source inside the building.
Figure 3.2 Building Definition Window
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3.3.1 Building Parameters
All the parameters may be integer or real. 0X points towards the east and 0Y
towards the north, with the source at (0,0). See Figure 3.3.
(i)
X co-ordinate of the centre of the building
X co-ordinate of the centre of the building, relative to the source which
is located at (0,0)
Minimum = -1000 m
Maximum = 1000 m
Default
= 0m
(ii)
Y co-ordinate of the centre of the building
Y co-ordinate of the centre of the building, relative to the source which
is located at (0,0)
Minimum = -1000 m
Maximum = 1000 m
Default
= 0m
(iii) Effective height of the building (m)
The user should decide an appropriate value. Figure 3.4 shows a
cautious approach.
Minimum = 0 m
Maximum = 500 m
Default
=0m
(iv)
Effective length of the building (m)
Length of the building (not necessarily larger than the width).
Minimum = 0 m
Maximum = 1000 m
Default
= 0m
(v)
Effective width of the building (m)
Width of the building (not necessarily smaller than the length).
Minimum = 0 m
Maximum = 1000 m
Default
= 0m
(vi)
Angle made by the Length to North (°)
Angle between the building length and 0Y, measured clockwise. The
length is not necessarily the longest side of the building, but is the side
defined as the length in the Buildings screen.
Minimum = 0 °
Maximum = 360 °
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Figure 3.3 Definition of building parameters
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Figure 3.4
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Effective height of building
15
3.4
Saving the data and running the model
Before running the model the data must be saved as an *.SPL file. To save the data
select Save As from the File menu. You will be asked to specify a name and
location for the *.SPL file.
To run the model, select Run from the File menu. During the run, messages are
displayed in a run window (Figure 3.5). Figure 3.6 shows the message displayed at
the end of the run. To exit the run window, click on ‘Yes’. To scroll back and read
the messages displayed during the run, click ‘No’.
Figure 3.5 Run window
Figure 3.6 Message displayed at the end of a run
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Section Four: Output
SECTION FOUR: OUTPUT
4.1
Description of output files
The output files can be opened in a text editor or spreadsheet directly from the
interface, by selecting Numerical results from the Results menu. The editor
or spreadsheet in which the results will be displayed by default can be changed
by selecting Preferences….Viewing Output from the File menu.
4.1.1 *.CSV (Short term output)
This file gives the short term concentrations of each pollutant at each
downstream distance for a range of atmospheric stabilities. For details of the
meteorological conditions, see §6.1. The file is in comma-separated format
and can be viewed using a spreadsheet such as Excel, or a text editor. At the
start of the file, all the modelled pollutants are listed. The pollutant emission
rates, output units, and a factor for conversion between g/m3 and the output
units (for internal use by the interface) are also given. Tables of output for
each pollutant follow, with downstream distance in metres and concentration
data in the specified output units in the columns.
The data may be viewed graphically using the line plotting facility (see
§4.2.1).
4.1.2 *.SCN (Long term output)
This file contains long term concentration data, for comparison with AQS and
EU limits and guidelines, or specified by the user using the General output
option.
A separate set of concentration data is given for comparison with each AQS or
EU limit, and for each General output option selected. This means that there
may be some duplication of results. For example, if modelling NO2 with AQS
and EU selected, the annual average concentrations of NO2 will be given twice
since both sets of limits include a limit on annual average NO2 concentrations.
A full numbered list of the long term output datasets is given in the *.LOG file.
The file is in comma-separated format. The data is in landscape format, with x
co-ordinates arranged horizontally and y co-ordinates vertically. This enables
the user to visualise how the concentration varies over the domain, and is in a
suitable format from which to create contour plots in a spreadsheet such as
Excel (see §4.2.2).
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4.1.3 *.GLT (Long term output)
This file is for use by the contour plotting link to Surfer. It contains the same
long term concentration data as the *.SCN file (see §4.1.2), in a column format
suitable for contour plotting in Surfer. See §4.2.3 for information on using the
contour plotting link.
4.1.4 *.MAX (Worst case concentrations)
This file contains information on the worst case short and long term
concentrations. Firstly tables of the maximum short term concentrations, if
calculated, and the downstream distances at which they occur for each
meteorological condition are given for each pollutant.
Next a table of the maximum long term concentrations, if calculated, is given.
This lists the maximum concentrations and the output points where they occur
for each long term output dataset, alongside the appropriate limit values, so it
is easy to see at a glance whether any of the limits have been exceeded.
The long term concentrations are calculated using around 600 meteorological
conditions (see §6.1). At the end of the *.MAX file, details of the condition
resulting in the highest concentrations are given. The wind speed and
direction, surface heat flux, boundary layer height and a short description of
the met conditions (e.g. ‘neutral’, or ‘very convective’) are listed, along with
the concentration of each pollutant for this condition.
4.1.5 *.LOG (Log file)
The log file contains a summary of the data entered into the model, and the
date and time at which the run started and ended at the top and bottom of the
file.
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4.2
Graphical output
4.2.1 Line plotting facility
The ADMS-Screen 3 line plotting facility displays the short term
concentrations given in the *.CSV file as graphs of concentration against
downstream distance. It is accessed by clicking on the Graphics tab in the
interface (Figure 4.1). To plot a graph, select a *.CSV file, then select one
pollutant and the meteorological conditions. Results for more than one
meteorological condition can be plotted on the same graph. Click on Plot
graph to create and view the graph (Figure 4.2). The type of axes (logarithmic
or linear), scale, captions etc may be altered using the Graph Setup option.
Clicking on Show graph displays the last graph created. To return to the
interface click Close.
Figure 4.1 Line plotting interface
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Figure 4.2 Graph screen
4.2.2
Contour plotting in Excel
The long term concentration data given in the *.SCN file is in a format suitable
for contour plotting in Excel. To create a contour plot, open the *.SCN file in
Excel as a comma-separated file. Locate the data to be plotted, and select all
the data, including the row of x co-ordinates and column of y co-ordinates
(Figure 4.3). Then select Insert….Chart and follow the steps in the Chart
Wizard, selecting Surface for the chart type and Contour for the chart subtype. An example contour plot is shown in Figure 4.4.
The contour levels may be changed by double-clicking on the chart legend to
display the Format Legend screen, then choosing the Scale tab. The colours
may also be edited, by double-clicking on the squares of colour in the chart
legend, to display the Format Legend Key screen.
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Figure 4.3 Selecting data from a *.SCN file for contour plotting in Excel
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CHIMNEY.SCN: 98th percentile concentrations of NO2 (ug/m3)
Y= 1000
Y=
800
Y=
600
Y=
400
Y=
200
Y=
0
24-28
20-24
16-20
12-16
8-12
4-8
0-4
Y= -200
Y= -400
Y= -600
Y= -800
Y= -1000
X= -1000
X= -800
X= -600
X= -400
X= -200
X=
0
X=
200
X=
400
X=
600
X=
800
X= 1000
Figure 4.4 Example Excel contour plot
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4.2.3
Contour plotting link to Surfer
The ADMS-Screen 3 contour plotting link displays the long term
concentrations given in the *.GLT file (see §4.1.2 and §4.1.3) as contour plots
using the program Surfer. Surfer may be purchased through CERC. The
contour plotting facility is accessed by selecting Contour plotting from the
drop-down Results menu. The interface is shown in Figure 4.5.
To create a contour plot, select a *.GLT file then select a dataset to plot. The
pollutant name, concentration level (e.g. 99.9th percentile, annual average),
units and averaging time for each dataset are displayed in the Dataset screen.
Each dataset also has an index number referring to the limit against which the
results should be compared. The limits are listed in the *.LOG file. After
selecting a dataset, click Plot. Surfer will first grid the data and store it in a
*.GRD file. Then click OK to display the plot.
An example plot is shown in Figure 4.6. The title of the plot is automatically
generated from the *.GLT file name and the data displayed in the Dataset
screen.
For further details on using Surfer to create and edit contour plots, see
Appendix C.
Figure 4.5 Contour plotting interface
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c:\progra~1\admssc~3\CHIMNEY.glt
1 NO2 Annual average
µg/m³
- 1hr
1000
800
600
1.40
400
1.20
Metres
200
1.00
0
0.80
-200
0.60
-400
0.40
-600
0.20
-800
-1000
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Metres
Figure 4.6 Example Surfer contour plot
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Section Five: Examples
SECTION FIVE: EXAMPLES
Two example *.SPL files are supplied with ADMS-Screen 3, chimney.SPL and
build.SPL, and these are discussed below.
5.1
Simple example stack chimney.SPL
Figure 5.1 Data screen for chimney.SPL
Figure 5.1 shows the completed Data screen for the example of a stack with no building
effects. The worst case results file chimney.MAX shows that the maximum short term
concentrations of 174µg/m3 for NO2 and 313µg/m3 for SO2 occur for met condition A.
Plotting the results shows the variation in concentration over the different conditions
(Figure 5.2). The worst case long term concentrations table shows that the AQS 2005
objective for the 99.9th percentile of SO2 (266µg/m3) is predicted to be exceeded; the
maximum value is 274µg/m3. Figure 5.3 shows a contour plot of the 99.9th percentile
concentration of SO2. The 266µg/m3 contour is marked, showing that there is only a
small region where the limit value is exceeded. The limits for NO2 are not exceeded.
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Figure 5.2 Downstream concentrations of SO2 for chimney.SPL
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11 SO2 99.9th percentile µg/m³
- 900s
1000
800
600
400
266.00
200
Metres
200.00
0
150.00
-200
-400
100.00
-600
50.00
-800
-1000
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Metres
Figure 5.3 99.9th percentile concentrations of SO2 for example.spl
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5.2
Stack with building effects
build.SPL
ADMS-Screen 3 can model the effect of one rectangular building on the dispersion.
Figure 5.4 shows the completed Building Definition menu for the example build.SPL.
Figure 5.4 Building Definition window for build.SPL
The worst case concentrations output file build.MAX shows that the maximum short
term concentrations occur under very convective conditions. The long term results show
that several of the limits are predicted to be exceeded. The highest hourly average
concentrations of 317µg/m3 for SO2 and 198µg/m3 for NO2 occur under convective
conditions.
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Section Six: Technical Summary
SECTION SIX: TECHNICAL SUMMARY
6.1
Meteorological data
For short term concentrations, seven meteorological conditions corresponding to a wide
range of stability conditions are used. These are independent of the location selected in
the interface, as the purpose of the short term results is to give an indication of the range
of predicted concentrations for different meteorological conditions. A wind direction of
270° (i.e. wind from the west) is used. Table 6.1 gives details of the seven conditions,
which correspond approximately to Pasquill-Gifford stability categories A-G.
For long term concentrations, one of a number of prepared meteorological data files is
used, depending on the location selected by the user. Further details of the datasets are
given in Appendix B. The files each contain around 600 meteorological conditions and
associated frequencies of occurrence, covering 12 wind directions (0° to 330° in steps of
30°) and a range of stabilities. The data files are created by analysing 10-year statistical
datasets supplied by the UK Met Office and combining similar conditions while
ensuring that the conditions likely to produce the highest concentrations are retained.
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Pasquill
Fθ0
h
Stability
1.
113
1300
vC
A
2.
84
900
C
B
5.
74
850
sC
C
5.
0
800
N
D
3.
-10
400
sS
E
2.
-6
100
S
F
1.
-0.6
100
vS
G
U
Category*
Table 6.1 Meteorological conditions for short term calculations
*Approximate equivalent Pasquill stability category.
U
= wind speed (m/s)
Fθ0 = surface heat flux (W/m2)
h
= boundary layer height (m)
Stability:
S stable
N neutral
C convective
s slightly
v very
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6.2
Parameterisation of the boundary layer
In ADMS the boundary layer is characterised by the boundary layer height h
and the Monin-Obukhov length LMO, not by a Pasquill-Gifford stability
category. The Monin-Obukhov length is defined as
− u*3
LMO =
κ gFθ 0 / (ρ c p T0 )
(6.2)
where u* is friction velocity at the earth’s surface, κ (=0.4) is the von Karman
constant, g is the acceleration due to gravity, Fθ0 surface heat flux, ρ and cp
are respectively the density and specific heat capacity of air and T0 the near
surface temperature.
In unstable or convective conditions, the Monin-Obukhov length is negative.
Then, the magnitude of the length is a measure of the height above the
ground above which convective turbulence that is, turbulent motions caused
by convective motions, is more important than mechanical turbulence
generated by friction at the earth’s surface.
In stable conditions the Monin-Obukhov length is positive. Then it is a
measure of the height above the ground above which vertical turbulent
motion is greatly inhibited by the stable stratification.
This approach to boundary layer stability, whereby the boundary layer
structure is defined in terms of two variables, z/LMO and z/h, supersedes the
Pasquill-Gifford formulation, and differs crucially from it in allowing the
variation of boundary layer properties with height to be included.
6.2.1 Boundary Layer Structure
ADMS calculates boundary layer variables, Table 6.3, at different
heights. Vertical profiles are expressed as functions of z/LMO and z/h
and have been derived from experimental data. These functions are,
in turn, called by other modules.
Plume spread parameters σy and σz are calculated using the boundary
layer variables and hence vary with source and plume height. This
contrasts with the approach in models which use Pasquill categories in
which values of σy and σz are obtained from measured profiles of σy
and σz.
February 2004
31
U(z), dU/dz, d2U/dz2
Mean wind and derivatives of mean wind speed
σu(z), σv(z), σw(z)
Root mean square (r.m.s.) turbulent velocities
Λv(z), Λw(z)
Turbulent length scales
ε(z)
Energy dissipation rate
TL(z)
Langrangian time scale
N(z)
Buoyancy frequency
T(z)
Temperature
ρ(z)
Density
Table 6.3 Boundary layer variables
February 2004
32
6.3
Mean concentration calculations
6.3.1 Dispersion Parameters
Field experiments and research have shown that the way dispersion parameters,
σy and σz vary with downwind distance from a point source depends on the state
of the atmospheric boundary layer, the boundary layer height (h), the height of
the source (zs) and the height of the plume as it grows downwind. This approach
is in contrast to older methods described in NRPB report R91 and used in the
model ISC, in which the effect of the source height is not taken into account
when calculating the width and depth of the plume.
There is no general theory or even generally accepted semi-empirical expression
that describes the dispersion from source at all heights within the boundary layer
(0 < zs < h), in all conditions of the atmospheric stability and over the complete
range of distances from the source extending to about 30km downwind. In
developing ADMS the approach adopted is first to use formulae that have been
developed and broadly accepted for specific ranges of the parameters zs/h, h/LMO
(stability) and x/h (downwind distance). Interpolation formulae have then been
constructed to cover the whole range.
6.3.2 The Stable and Neutral Boundary Layer
All the turbulence in the stable boundary layer is mechanically generated i.e.
there is no generation of turbulence due to convective motions. Usually, the
level of turbulence decreases with height, as the relative effects of
stratification increase, although it can be enhanced by wave motions at the top
of the boundary layer. (The effect of wave motions is not considered by
ADMS.)
Concentration distribution
The distribution of the concentration profile is a Gaussian plume
with reflections at the ground and the inversion layer.
C=
Qs
2π σ y σ z U
e
- y 2 / 2 σ y2
{ e- ( z - z s
) 2 / 2 σ z2
+ e- ( z + z s
) 2 / 2 σ z2
(6.4)
+ e- ( z + 2 h -
February 2004
2
zs ) / 2 σ z
2
+ e- ( z - 2 h + z s
2
) / 2σ z
2
+ e- ( z - 2 h -
2
zs ) / 2 σ z
2
}
33
Plume Spread parameters
σz, the vertical dispersion parameter at the mean height of the plume,
zm, is linked directly to the vertical component of turbulence, σw, and
the travel time from the source, t, by the relationship.
1
N 2t2 
σ z = σ wt  2 +

1 + 2 Nt 
b
−1 / 2
(6.5)
where N and σw are the buoyancy frequency and r.m.s. vertical
turbulent velocity zm. The factor b ensures a smooth transition
between the solution for surface releases and elevated releases.
The transverse dispersion parameter, σy, is given by
σ 2y = σ 2y + σ 2y .
t
(6.6)
w
In stable flows, h/LMO > 1,
(
σ y = σ v t 1 + ( 15.6 )1/3 u* t L MO / h2
t
)
- 1/ 2
(6.7)
and in neutral flows, -0.3 ≤ h/LMO ≤ 1.0.
(
σ y = σ v t 1 + ( 15.6 )1/ 3 u* t /h
t
)
- 1/ 2
(6.8)
The spreading due to turbulence σyt is assumed to become linear with
respect to time t when h/LMO is large, i.e. in very stable flows.
The spread due to variations in mean wind direction, σyw is equal to
σθx. σθ, the standard deviation of the mean wind direction, is
calculated by the met pre-processor using the following expression:
σ θ = 0.065
February 2004
7 T / U 10
(6.9)
34
T is the averaging time in hours and U10 is the mean wind speed at a
height of 10m.
Near-field to far-field transition
In neutral conditions the part of the plume which does not have
sufficient momentum or buoyancy to penetrate the top of the boundary
layer is effectively confined within the boundary layer, because
material reaching the top of the layer is reflected downwards.
Sufficiently far from the source, after parts of the plume have been
reflected at the ground and at the top of the boundary layer, the
vertical variation in concentration of the pollutant is so small as to be
negligible. This occurs approximately at the downwind distance
where σz ≈ h (in fact, where σz =1.5h). Downwind of this point the
plume is considered to grow horizontally as a vertical wedge as if
from a uniform line source, height h, rather than as a cone, so the
variation with z in equation (6.4) is ignored.
6.3.3 The Convective Boundary Layer
Field experiments of diffusion from elevated sources in the convective boundary
layer have confirmed earlier laboratory and computational studies that the form
of the vertical profiles of concentration are skewed and significantly nonGaussian. This changes the distribution of concentration and is important for
evaluating maximum ground level concentrations from elevated releases.
Concentration distribution
In the convective boundary layer (CBL) the probability distribution of
the vertical velocity and, hence, the concentration distribution is
non-Gaussian, or skewed. The non-Gaussian distribution ensures
that, for elevated sources, the height within the plume at which the
concentration is a maximum descends as the plume moves downwind,
whilst the plume mean height ascends. After the height of the
maximum concentration reaches the ground it can rise again.
The concentration is calculated as a weighted sum of two
contributions; firstly CCBL the value of the concentration per unit
source strength from the convective model, and secondly CNBL the
value of concentration per unit source strength derived from equation
(8.3.1) for the neutral-stable layer. For the transition from CBL to
neutral boundary layer (NBL) (h/LMO > -0.3), we let the concentration
C be given by:


h
+ C NBL 
C = Qs C CBL
LMO


February 2004

/  1 +

h
LMO




(6.10)
35
Spread Parameters
The transverse dispersion parameter σy is calculated in two parts, the
first for dispersion due to convection σyc, the second due to
mechanically driven turbulence σyn
c
c
t

0.75 1 / 3 w* 
h



t
(15.6 )1 / 3 u* 
h

σ y = σ v t 1 +
n
m
−1 / 2


σ y = σ v t 1 +
(6.11)
−1 / 2
(6.12)
σvc and σvm are the r.m.s. (root mean square) horizontal velocities due
to convection and mechanically driven turbulence respectively. An
additional term σyw is included to allow for the variation in the wind
direction, and is the same as that given in equation (6.11)
The total transverse spread is given by
σ y2 = σ y2 + σ y2 + σ y2
n
c
w*
(6.13)
For the vertical spread σz, the skewed nature of the probability
distribution function for the vertical turbulent velocity w lead to the
definition of σw+ and σw- for the upwards and downwards velocities.
Then σ z+ = σ z _ = σ w _ t and σ w− t are defined and used in the
calculation of CCBL, the concentration profile.
Near-field to far-field transition
The transition to a far-field model, where the source is equivalent to a
line source of height h, and uniform strength is assumed to occur when
σz =1.5h.
February 2004
36
6.4
Plume Rise Module
The Plume Rise Module predicts the rise trajectory and enhanced dilution of a
continuous emission of hot gaseous material. The underlying theory uses an
integral model, and includes penetration of inversions. It takes into account the
effect of plume buoyancy and momentum in generating plume rise.
Integral conservation equations are solved for the fluxes of mass, momentum
and heat, assuming the plume to be a continuous, bent-over cone of circular
cross-section across which plume properties velocity, density etc. are uniform,
i.e. a “top-hat” profile. Entrainment of ambient air takes place due to the
plume's motion relative to its environment and to atmospheric turbulence. The
external velocity and temperature fields may vary with height.
Figure 6.14 Plume Rise Model
The Plume Rise Module is initialised from source conditions: exit diameter and
emission velocity or volume flow rate and temperature or density. The
equations are then solved numerically by the method of Runge-Kutta using a
variable internal time-step.
February 2004
37
6.5
Building Effects Module
The building effects module is used to calculate the dispersion of pollution
from sources near large structures, out to a distance of about 60 building
heights. The ADMS model of building effects has the following features:
(1)
The building is defined by the user in terms of its height, length, width
and orientation. For each wind direction the building is modelled as an
effective wind-aligned building. The along-wind and streamwise
dimensions are determined from the dimensions of the building.
(2)
The disturbed flow field consists of a recirculating flow region or
cavity in the lee of the building, with a diminishing turbulent wake
downwind.
(3)
Concentrations within the well-mixed recirculating flow region are
uniform and based upon the fraction of the release which is entrained.
(4)
Concentrations further downwind are the sum of those from two plumes:
a ground-level plume from the recirculating flow region and an elevated
plume from the non-entrained remainder. The turbulent wake reduces
plume height and increases turbulent spread.
(5)
The concentration is set to zero within the user defined building.
The building effects module interacts with the rest of ADMS, using the
underlying concentration profiles, but with modified plume height and plume
spread.
The stages in the analysis of building effects are illustrated in Figure 6.15.
February 2004
38
Figure 6.15 Stages in the analysis
6.5.1 Stack Induced Downwash
The algorithm used to predict stack tip downwash is described in the following
section. It is only used in the model if the building effects module is used.
February 2004
39
The flow field and pressure field around a stack can influence the plume rise of
the emission by reducing the mean height of the plume just downwind of
emission. Only releases of relatively small upward momentum are affected,
since all other emissions rise rapidly away from the zone of influence.
Effective Stack Height Algorithm
The algorithm employed is that used in many other models and applies to
point sources only.
If the emission velocity ratio, wS/UH, is less than 1.5, the source height is
corrected (reduced) by ∆zS
∆zS
=
=
2.(wS/UH) -1.5}.DS
0
when wS/UH < 1.5
when wS/UH > 1.5
Terminology:
DS
outside diameter of stack
UH
approach flow speed at height of stack top
wS
emission speed
∆zS
correction to stack height
If wS/UH > 1.5 the correction is not applied, ie the effect of downwash is
ignored. It is also not applied if the stack diameter is greater than 25% of the
building height.
However, it is not a model of building induced downwash, and should not be
used as such.
6.5.2 Limitations of the building effects module
(i)
The buildings module is based on experiments in which there was one
dominant site building and several smaller surrounding buildings less
important for dispersion
(ii)
The module has been adapted to handle thin buildings i.e. buildings or
height greater than 3 times the building width or length.
(iii) The stack downwash algorithm is quite widely used in dispersion models
although it has never been adequately evaluated.
(iv) The stack downwash algorithm is only intended for use with stack
emissions, though it could be applied, at the user's discretion, to other
cases, such as cooling tower plumes.
February 2004
40
(v)
February 2004
Strictly speaking, the stack should be circular in cross section, though
again it could be applied, at the user's discretion to other cases, such as
stacks of square cross section.
41
6.6
Statistics: Long term average and percentiles
Statistical meteorological data are supplied with the wind direction ‘binned’
into 30 degree sectors. For example, a wind direction of 90° in the dataset
could correspond to any measured wind direction between 75° and 105°. To
account for this, each 30° sector is split into five intervals of 6° and a separate
set of concentrations is calculated for each of the five wind directions. For
example, for the sector centred on 90°, the five wind directions would be 78°,
84°, 90°, 96° and 102°. The frequency of each meteorological condition is split
evenly between the five wind directions.
For each meteorological condition and wind direction and associated frequency
ƒ, (normalised by dividing the sum of the frequencies), the concentration at
each point is calculated, say C(x,y,z). Then the long term mean concentration
at that point, Cmean(x,y,z) is given by the sum of Cƒ over all the met conditions.
To calculate the concentration at each point corresponding to a specified
percentile p at ground level, say Cp(x,y,z), the values of C(x,y,z,) at one point
for each combination of meteorological variables are considered along with
their normalised frequency of occurrence ƒ. First of all the concentration
values are arranged in descending order (i.e. highest at the beginning, lowest at
the end) and the values of ƒ rearranged accordingly. Then, starting at the
highest concentration, the frequencies are summed until their cumulative value
is p/100.
February 2004
42
6.7
Calculation of concentrations for comparison with limit values
ADMS-Screen 3 calculates long term concentrations for direct comparison
with UK Air Quality Strategy and EU limit values. These are listed in a
separate document accessible from the user interface. The limits are mostly
expressed as annual averages, or as percentiles of hourly average
concentrations. However, a few refer to percentiles of concentrations
averaged over periods less than or greater than 1 hour.
All the short term concentrations calculated by ADMS-Screen 3 are hourly
average concentrations. This leads to a conservative estimate of the
concentrations averaged over longer periods. To estimate the 15 minute
average concentration for comparison with the UK Air Quality Strategy
objective for SO2 (99.9th percentile of 15 minute averages), the hourly average
concentration is multiplied by a constant factor of 1.34. Use of this factor is
suggested in the Environment Agency report ‘Guidance for Estimating the Air
Quality Impact of Stationary Sources’ (ref. 8). No adjustment is made to the
downstream position of the maximum concentration.
February 2004
43
Appendix A: Limits and Guidelines
APPENDIX A: LIMITS AND GUIDELINES
A list of the UK Air Quality Strategy objectives and EU limits and guidelines
included in ADMS Screen 3 is shown in Table A.1. This information is also
accessible directly from the interface, by clicking on the Limits menu.
Table A.1 Pollutant Limits and Objectives included in ADMS-Screen 3
UK Air Quality Strategy (AQS)
Objective 2005
Objective 2005
Objective 2000
Objective 2000
Objective 2004
Objective 2004
Objective 2005
Objective 2004
Objective 2004
Objective 2003
Objective 2003
Objective 2003
Objective 2004
Objective 2008
Pollutant
NO2
NO2
NOx
SO2
SO2
SO2
SO2
PM10
PM10
CO
Benzene
1,3-Butadiene
Lead
Lead
Title
Value Units
Annual average
40 µg/m3
18 exceedences of the hourly average (99.8th percentile)
200 µg/m3
Annual average (ecosystems and vegetation)
30 µg/m3
Annual average (ecosystems and vegetation)
20 µg/m3
24 exceedences of the hourly average (99.7th percentile)
350 µg/m3
3 exceedences of the 24 hour average (99.2th percentile)
125 µg/m3
35 exceedences of the 15 minute average (99.9th percentile)
266 µg/m3
Annual average
40 µg/m3
35 exceedences of the 24 hour average (90th percentile)
50 µg/m3
100th percentile 8 hour average (running)
11.6 mg/m3
Annual average (running)
16.25 µg/m3
Annual average (running)
2.25 µg/m3
Annual average
0.5 µg/m3
Annual average
0.25 µg/m3
Pollutant
NO2
NO2
NOx
SO2
SO2
SO2
PM10
PM10
PM10
PM10
Lead
Title
Annual average
Hourly average (12 exceedences)
Annual average
Annual average (ecosystems)
99.7th percentile of hourly averages
99.2th percentile of 24 hour averages
Annual average (PM10)
90th percentile 24 hour average (PM10, 35 exceedences)
Annual average (PM2.5)
96th percentile 24 hour average (PM2.5, 14 exceedences)
Annual average (health)
EU
Limit 2010
Limit - current
Limit 2000
Limit 2000
Limit -current
Limit 2005
Limit - current
Limit - current
Limit - current
Limit - current
Limit - current
February 2004
Value
Units
40 µg/m3
200 µg/m3
30 µg/m3
20 µg/m3
500 µg/m3
125 µg/m3
45 µg/m3
50 µg/m3
30 µg/m3
40 µg/m3
0.5 µg/m3
44
Appendix B: Meteorological Data
APPENDIX B: METEOROLOGICAL DATA
As described in Section 6.1, the meteorological datasets used for long term
calculations are created by analysing 10-year statistical meteorological datasets
supplied by the UK Met Office. These 10-year datasets are in turn produced from
observed meteorological data from measurement sites spread throughout the UK.
Table B.1 gives details of the meteorological measurement site for each region. The
latitude, surface roughness and height of the wind measurements are used by the
model in processing the meteorological data. Note that the surface roughness given
here is the value at the meteorological measurement site – the user should enter a
value appropriate for the source site in the interface. Figures B.2 – B.7 show wind
roses for each site.
Region
Site latitude (°)
Site surface
roughness (m)
Wind
measurement
height (m)
10
Northern Ireland
54
0.2
Scotland
56
0.2
10
Northern England
53
0.25
10
Central England
52
0.25
10
East Anglia
52
0.2
10
Southern England
52
0.2
10
Table B.1 Measurement site data
February 2004
45
Figure B.2
Wind rose for Northern Ireland
Figure B.3
February 2004
Wind rose for Scotland
46
Figure B.4
Figure B.5
February 2004
Wind rose for Northern England
Wind rose for Central England
47
Figure B.6
Figure B.7
February 2004
Wind rose for East Anglia
Wind rose for Southern England
48
Appendix C: Surfer Tips
APPENDIX C: SURFER TIPS
This appendix is intended as a quick guide to editing Surfer contour maps and adding
features to them. This is not a comprehensive guide to all the features of the Surfer
software package and it is recommended that users refer to the Surfer user manual
when more detailed information is required.
Creating a contour plot
Contour plots in Surfer are generated via the ADMS-Screen 3 Contour Plotting
interface, shown in Figure C.1 below.
Figure C.1 ADMS-Screen 3 contour plotting interface
Select the Dataset to plot and click on the Plot button. The ADMS-Screen output
data is converted to a *.GRD file which is required for Surfer to produce the contour
plot. The default name for the *.GRD file is the same as the *.SPL file it is associated
with. Once the contour plot has been generated, the *.GRD file is no longer needed
and may be overwritten when creating new plots. Click OK to confirm the *.GRD
file name and display the contour plot. Note that Surfer always produces an initial
plot, ‘Plot 1’, on starting up, with nothing in it. Your plot will be called ‘Plot 2’ by
default.
February 2004
49
The plot can be saved as a *.SRF file. You may then return to it to edit it at any time
to, for example, change the contour levels plotted or add text. An example plot is
shown in Figure C.2.
1 NO2 Annual average
µg/m³
- 1hr
1000
800
600
1.40
400
1.20
Metres
200
1.00
0
0.80
-200
0.60
-400
0.40
-600
0.20
-800
-1000
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Metres
Figure C.2 Example contour plot
Editing features of the contour plot
Editing contour levels
By default, the contour plot will usually show around 8 contour levels. These will be
coloured from yellow for the minimum contour level to red for the maximum contour
level as shown in Figure C.2.
The default contour levels are selected to match the data, but can be edited by the
user. For example you may wish to plot a concentration level lower than the
minimum shown in the contour plot or a particular range of levels. To do this, doubleclick on the contour map to show the screen in Figure C.3.
February 2004
50
Figure C.3 Surfer Contour Map editing screen
To change the range of levels, click on the Level… button to specify regular
intervals as shown in Figure C.4 and click on OK to return to Figure C.3 then click on
OK again to apply the new range of levels to the contour plot.
Figure C.4 Surfer Contour Levels editing screen
This may change the colours of the filled contours to a grey/black scheme. The
colours can also be edited, as outlined later.
To edit the value of a particular level, double-click on that number in the Level…
column and change the value to the one you want.
To add a new contour level between two existing levels, click on the higher of the
two levels and then click on the Add button. The new contour will be added half way
between the selected contour and the one below it.
The contour levels can be saved as a *.LVL file. Click on Save and save the level
file with a unique name. This will not only save the contour levels but also the choice
of colours, pattern of the filled contours, labels, line thickness and colour, label fonts
etc. The new level file can then be applied to other contour plots so that comparisons
can be made with results for different modelling scenarios. To do this, double-click
February 2004
51
on the new contour plots to enter the screen shown in Figure C.3 and click on the
Load button, then select the particular *.LVL file required.
Editing Contour Labels
By default the label format is usually set to label contours with numbers up to two
decimal places. If the numbers in the ADMS-Screen 3 output file are very small, then
the contours will all be labelled 0.00 on the plot. It is a common mistake to think that
there is a fault in the software but the solution is to change the labelling format.
In Figure C.3 click on the Label… button to open the screen shown in Figure C.5.
Figure C.5 Surfer Contour Labels editing screen
Click on the Format… button to open the screen shown in Figure C.6.
Figure C.6 Surfer Label Format editing screen
Here the Label format is selected. The user can choose to add more decimal digits to
the labels, or it may be more appropriate to choose the exponential format for very
small numbers.
Click on OK to return to Figure C.5. Click on Font… to open the screen shown in
Figure C.7.
February 2004
52
Figure C.7 Surfer Text Attributes editing screen
Here the user can choose the font style, colour and size for the contour labels.
Editing the Filled Colours and Patterns
To edit the colours and patterns of contour plots double –click on the contour plot to
open the screen in Figure C.3. Click on the Fill… button to open the screen shown in
Figure C.8.
Figure C.8 Surfer Fill Spectrum editing screen
Click on the Minimum coloured box to enter the screen shown in Figure C.9.
Figure C.9 Surfer Fill Attributes editing screen
In this Fill Attributes screen, the user can choose a colour for the minimum contour
level. The pattern, which is solid by default, may also be edited. Click on OK and
February 2004
53
repeat for the maximum contour level. The result will be a ramp of colours ranging
from the minimum to the maximum colour.
Note that the Fill Contours box should be checked in Figure C.3 for the colours to
show on the contour plot.
Alternatively, the user can specify a unique colour for every contour level. Beneath
the Fill… button in Figure C.3, the user can double click on each individual coloured
box to open the screen of Figure C.9. A unique colour than then be chosen for each
level.
Editing the Colour Scale
When a contour plot has filled colour contours, it is useful to include a colour scale on
the plot. This is included by default when contour plots are generated from the
ADMS-Screen Contour Plotting interface. Similar to the contour labels, the colour
scale labels are also numbers up to two decimal places. To change the format of these
labels double-click on the colour scale bar to open the screen shown in Figure C.10.
Figure C.10 Surfer Colour Scale editing screen
The label format and font can be changed in the same way as the contour line labels.
February 2004
54
Appendix D: References
APPENDIX D: REFERENCES
1.
CERC 1998. ADMS 3 Technical Specification.
2.
Carruthers D.J., Holroyd R.J., Hunt J.C.R., Weng W-S., Robins A.G., Apsley
D.D., Thompson D.J. and Smith F.B. 1994. UK-ADMS: A new approach to
modelling dispersion in the earth's atmospheric boundary layer. Journal of Wind
Engineering and Industrial Aerodynamics 52 139-153. Elsevier Science B.V.
3.
Carruthers D.J., Holroyd R.J., Hunt J.C.R., Weng W-S., Robins A.G., Apsley
D.D., Smith F.B., Thomson D.J., and Hudson B.. 1991. UK Atmospheric
Dispersion Modelling System.
Proceedings of the 19th NATO/CCMS
International Technical Meeting on Air Pollution Modelling and its Application,
September 1991, in Crete, Greece (Edited by Han van Dop and George Kallos).
Plenum Publishing Corporation, New York.
4.
J.C.R. Hunt, R.J. Holroyd, D.J. Carruthers, Robins A.G., Apsley D.D., Smith
F.B. and Thomson D.J. 1990. Developments in Modelling Air Pollution for
Regulatory Purposes Proceedings of the 18th NATO/CCMS International
Technical Meeting on Air Pollution Modelling and its Application, 1990, in
Vancouver, Canada
5.
McHugh C. A., Carruthers D. J. and Edmunds H. A. 1997 ADMS and ADMSUrban Workshop on Operational Short-range Atmospheric Dispersion Models
for Environmental Impact Assessment in Europe, Mol, Nov. 1994, published in
Int. J. Environment and Pollution Vol 8, Nos. 306, pp437-440
6.
Robins A. G., Carruthers D. J. and McHugh C. A. 1997 The ADMS Building
Effects Module Int. J. Environment and Pollution Vol 8, Nos. 3-6
7.
F. Pasquill and Smith F. B. 1983. Atmospheric Diffusion: Study of the
dispersion of windborne material from industrial and other sources. 3rd
edition, Ellis Horwood Ltd, Chichester.
8.
Environment Agency 1999. Guidance for Estimating the Air Quality Impact
of Stationary Sources.
February 2004
55

ADMS Screen 3

Transcription

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