| Calculations in a street canyon |
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AEOLIUS Full calculates a series of hourly concentrations of a
pollutant at a receptor in a street canyon
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Uses typical traffic data, emission factors, and hourly meteorological
data
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Gives results at a single receptor on the side of the street: the
program decides by means of wind direction and receptor bearing
across the street whether this is to be a windward or leeward side,
and outputs the relevant concentration
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All data times in GMT
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Traffic data for AEOLIUS Full must be presented as a one-week summary
of average flows, with a file for each vehicle type
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Vehicle speed is a one-week summary of representative speeds at
each hour through the week
Disk files - users are advised to:
- Ensure that the supplied master disk is write-protected
- Copy the files to another disk or the hard drive and keep the master
copy safe
- Edit their versions of the files (but keeping the same format)
- AEOLIUS Full needs five input files of the correct format (see later
for an example of each)
- Example of the first file accessed on the disk is "DATAFILE.DAT"
- contains a number of other filenames and data values, entered by
the user, which enables AEOLIUS Full to open the correct data files
and initialise some important site specific parameters
AEOLIUSF generates one output file whose name the user will specify.
Traffic units
Input data
Four other input data files (named by the user in DATAFILE.DAT) defining
the users own particular traffic flow situation and prevailing meteorological
conditions. A brief description of examples of each of these four data
files is given here:
SMALLVPH.DAT
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File must have two lines of textual information at its head
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Details the hourly-averaged frequency of small vehicles using the
street in question (7 days * 24 hours pieces of data)
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Units used by AEOLIUSF are number of vehicles per hour
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First data row has traffic counts from hour 0 to hour 1 in each
day of the week
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Second row is then hour 1 to hour 2, and so on
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Times are in GMT
LARGEVPH.DAT
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File must have two lines of textual information at its head
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Details the hourly-averaged frequency of large vehicles using the
street in question (7 days x 24 hours pieces of data)
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Units used by AEOLIUS Full are number of vehicles per hour
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First data row has traffic counts from hour 0 to hour 1 in each
day of the week
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Second row is then hour 1 to hour 2, and so on
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Times are in GMT
SPEEDMPH.DAT
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Must have two lines of textual information at its head
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Details the hourly-averaged speed of all vehicles using the street
in question (7 days x 24 hours pieces of data)
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Units used by AEOLIUS Full are miles per hour
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First data row has traffic speeds from hour 0 to hour 1 in each
day of the week
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Second row is then hour 1 to hour 2, and so on
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Times are in GMT · Fixed file format
BIRM0595.DAT
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Must have four lines of textual information at its head.
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Provides meteorological information year, month, day, hour, mean
wind direction (degrees), temperature (°C), pressure (millibars),
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10 metre wind speed (m/s) for each of the hours of each day considered
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Fixed file format
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One row per hour
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Times in GMT
The four lines of text at the top of each met. file are necessary,
they are provided so that the user can describe the origins of the meteorological
data.
Output data
The results file is named by the user in DATAFILE.DAT and can be changed
for each run.
POLL_MPH.DAT details the following information that was output
by the model:
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Year (4 digits)
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Month (1 or 2 digits; 1 = January)
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Date (1 or 2 digits)
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Hour of the day (1 or 2 digits; 0 = midnight at start of day; 23
= 11 pm, end of day) in GMT
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Average wind direction during that hour (degrees)
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Wind velocity at the street level (m/s)
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Wind velocity at the roof-top level (m/s)
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Total pollution concentration expected (ppb except CO: ppm, and
PM10: g/m3); if NO2 is specified as the pollutant species, then
the total pollutant concentration is broken down into three categories:
NO2, NO, and NOx
Users are advised to change the name of this file before each model
run to prevent the results from previous runs being overwritten.
Birmingham for May 1995
Here, the data files are representative of how the data would be configured
to model the combined pollution hour by hour from two vehicle types.
The traffic data are set up to give a typical weekly pattern for small
and large vehicles. There are different emission factors for each type.
All vehicles are given the same average speeds although these vary throughout
the week.
The meteorological data represent a short sample of observations from
Birmingham airport.
The results file shows hourly concentrations that were calculated at
the receptor. The NOx emission factor for large vehicles (9.23 g km-1)
was based on combining Medium HGV, Large HGV and Buses from Table 1b
of Buckland and Middleton (1997). The NOx emission factor for small
vehicles (1.429 g km-1 ) was for all others in the Table 1b. The values
were weighted according to the traffic flows in Table 1b and combined
into two categories, small and large.
When AEOLIUS Full was run for this example, they were multiplied by
the hourly traffic counts from files SMALLVPH.DAT and LARGEVPH.DAT to
give a combined emission for the canyon dispersion calculations. To
use different emission factors, the user simply edits the file DATAFILE.DAT.
Example data files
for Birmingham test run Appendix 1
Model comparison
The model has also been shown to reproduce the so-called standard values
for CO in Tables 2a, 2b of the nomograms by Buckland and Middleton (1997).
Appendix 2 shows
the DATAFILE.DAT needed to confirm that the program AEOLIUSF gave the
same result as in the nomogram (obtained from the early screening version
of AEOLIUS). Here, the emission factors for small and large vehicles
are taken from the bottom row of Table 1a in Buckland and Middleton
(1997). By setting both vehicle types to the same emission factor we
are effectively using a fleet averaged emission factor. Usually different
factors will apply, as was illustrated in the Birmingham example above.
To conduct this special calculation using a combined flow of 2,000 vehicles
per hour, traffic counts of small vehicles were set to 1881 vehicles
per hour (0.5225 vehicles per second), and large vehicles were set to
119 vehicles per hour (0.033 vehicles per second) for all times in the
week. The traffic speed was set to 11.185 mph (5 m s-1 ) at all times.
The wind speed was set to 4 m s-1 and wind direction and receptor bearings
set for parallel and perpendicular flow. Emission factors for CO were
representative of the combined fleet
(17.94 g km-1 ) This means the screening model AEOLIUS, the full model
AEOLIUSF, and the Tables 2a, 2b are all consistent with each other.
Other data are in
Appendix 2
References
Buckland A T (1997), Validation of a street canyon model
in two cities. Submitted to Environmental Monitoring and Assessment.
Buckland A T and Middleton D R (1997), Nomograms for calculating pollution
within street canyons. Submitted to Atmospheric Environment
Appendix 1:
Example data files for Birmingham test run
Appendix 2:
Example data files to show result for CO as in Table 2a, from Buckland
and Middleton (1997)
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