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ADVANCED MODULES
One of the most important advanced modules in ADMS-Urban is the chemistry
module. The following chemistry options are available:
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NOx – NO2 chemistry
In ADMS-Urban there two ways to model NOx chemistry.
The first is using a simple correlation scheme
(Derwent and Middleton, 1996) but the recommended option is to
use the 8 reaction Generic Reaction Set (Venkatram
et al., 1994) that includes reactions with ozone and
hydrocarbons.
Why use this module?
In most urban areas, the dominant pollution source is road traffic,
and the pollutants usually of major interest are NOx
and PM10. The NOx chemical reactions take
place over a relatively short time period and in order to get
accurate predictions of NO2 concentrations, NOx
chemistry should be taken into account. The Generic Reaction Set
predicts changes in Ozone concentrations that are also of interest.
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The Trajectory model
A simple Lagrangian Trajectory Model is used
to calculate background concentrations for the air approaching
the main modelling area. This model includes the effects of emissions,
chemistry, deposition and ozone entrainment.
Why use this module?
By nesting the main model domain within a larger domain, such
as a large urban conurbation, the Trajectory Model calculates
a spatially varying background ambient concentration that takes
into account the chemical reactions and processes occurring over
the larger domain.
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Sulphate chemistry
The reactions between SO2 and other compounds in the
air to produce particulates are based on those used in the EMEP
model (Tsyro, 2001).
Why use this module?
These reactions have a significant effect on the concentrations
of particulates in areas where there are a large number of industrial
sources emitting SO2 or downwind from a large emitter
of SO2.
Other advanced modules included in ADMS-Urban are:
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Street canyons
This module is based on the Danish Operational Street Pollution
Model (OSPM, Hertel and Berkowicz, 1990, Hertel et al, 1990).
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Complex terrain
This module is based on FLOWSTAR advanced airflow model which
calculates the change in mean flow and turbulence due to terrain
and changes in surface roughness (land use).
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Buildings
Users can include up to 10 dominant buildings. ADMS-Urban creates
an effective building for each point source from the user-defined
buildings and models the re-circulating flow in the lee of the
building, the cavity region, as well as the building main wake.
These modules are based on the latest understanding of
the way these features affect the movement of airflow around the sources,
and all have been shown to have considerable affect on observed concentrations.
Full details of the Technical Specification of these parts of the model
can either be found on the documentation
page of this site, or on request from CERC (enquiries@cerc.co.uk).
VERIFICATION
The ADMS-Urban model has been comprehensively verified
in a large number of studies. This includes comparisons with data from
the UK's Automatic Urban Network (AUN) during all of our consultancy
studies and specific validation exercises using standard field, laboratory
and numerical data sets. CERC is also involved in European programmes
on model harmonisation, and our models have been compared favourably
against other EU and US EPA systems.
For further details of verification studies that have been carried out,
please refer to the documentation page
of this site.
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