MODEL OUTPUTS
Pollution concentrations can be calculated for averaging times ranging
from seconds up to years. ADMS-Urban can calculate percentiles,
the number of exceedences of threshold concentrations
and rolling averages. These options allow users
to compare concentration results directly with appropriate limits,
for example those given by the UK NAQS, US NAAQS, EU or WHO.
Model results are usually first verified
by making comparisons with locally monitored
data. This can be done
by outputting results at receptor points corresponding to monitoring
site locations. Modelled and monitored concentrations can then
be compared as a time series plot. |
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Results created by ADMS-Urban are often presented as colour contour
plots. The intelligent gridding enables users to
model a large area yet obtain high spatial resolution in areas of
particular interest – in and around the roads. The ADMS-Urban
contour plots are an extremely effective way of communicating results
to decision makers, the public and other stakeholders.
WHY DO YOU NEED INTELLIGENT GRIDDING?
Intelligent gridding gives high resolution of results where it is
needed – in and around the roads. The three figures below
show an area of 1.4 km2 with approximately 5km length of roads being
modelled.
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The first figure shows concentration results using the
intelligent gridding option. You can see that the contours
reveal the shape of the roads and that the high concentrations
(i.e. those shown in yellow, orange and red) are fully resolved.
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The second figure shows the roads in red, and the output points
used to create the plot above as black dots.
Both the regular grid points and the extra intelligent gridding
points inside and either side of the road are shown.
The spacing of the intelligent gridding points
is related to the width of the road, and the user can vary the
along-road spacing.
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The final figure shows a contour plot of results using just
a regular grid with a resolution of approximately 70m. Although
the locations of the roads can be seen, results are in general
very ‘blobby’. This type of output is typical of other
roads models that do not have the intelligent gridding option. |
Using the GIS links, concentration results can be overlaid
onto maps in order to show the location of areas worst affected by
pollution.
MODELLING SCENARIOS AND
FUTURE YEARS
In most cases, ADMS-Urban is first used to model the emissions from
a ‘base case scenario’, that is, data (emissions, met,
background etc) are used to produce results that can be verified against
locally monitored data from a recent previous year or the current
year. Once the base case scenario has been validated, it is possible
to investigate different scenarios, for example:
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Impact of major development
ADMS-Urban is often used to compare air quality before and after
major developments. An emissions inventory is compiled using the
best available estimates for after the development. ADMS-Urban
allows many “What If?” scenarios to be tried out,
predicting concentrations at key receptors or across a wider area.
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Future years
The majority of air quality limits are objectives for future years.
These scenarios can be modelled in ADMS-Urban using the DMRB emission
factors for future years, future predictions from EMIT, or, the
user’s own estimate. Likely changes in traffic flows,
fleet compositions and background concentrations
if known, can also be included in the future scenarios.
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Traffic Management
If the predictions for future years indicate that concentrations
of certain pollutants are likely to exceed the objectives, it
is usual to consider traffic management and emission reduction
scenarios. For example, some local authorities in the UK are considering
introducing Low Emission Zones
within which only vehicles that have achieved a particular low-emission
standard are allowed. The effect on air quality of introducing
such measures can be investigated using ADMS-Urban. CERC’s
Emissions Inventory Toolkit, EMIT can be
used for investigating the effect on emissions.
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