CERC — Environmental Software and Services

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World leading software for urban air quality management

Model options

Advanced options include:

  • Urban chemistry
    • Fast reactions for NOx, O3, SO2
  • Features affecting urban flow and dispersion
    • Street canyon, tunnel and elevated roads modules
    • Allowance for the effects of complex terrain and changes in surface roughness
    • Allowance for the effects of the urban canopy
    • Allowance for the effects of buildings local to sources

These flow modules are based on the latest understanding of the way these features affect the movement of airflow and turbulence around the sources; all have considerable effect on observed concentrations.

Chemistry module

In many urban areas, the dominant pollution source is road traffic, and the pollutants usually of interest are NO2, NOx, O3, PM10 and PM2.5.

ADMS-Urban models NOx chemistry using the 8 reaction Generic Reaction Set (Venkatram et al., 1994) that includes reactions with ozone and VOCs.

The NOx chemical reactions take place over a relatively short time period and in order to calculate NO2 concentrations, NOx chemistry needs to be taken into account. The Generic Reaction Set also predicts changes in ozone concentrations.

ADMS-Urban also includes a SO2 chemistry module using a reaction set based on those used in the EMEP model (Tsyro, 2001).

These reactions generate significant concentrations of particulates in areas where there are a large number of industrial sources emitting SO2 or downwind of a large emitter of SO2.

Regional Chemistry

Background concentrations for the air approaching the main modelling domain may be considered using a regional air quality model automatically coupled to ADMS-Urban model using the regional model link, or by using ADMS's built in Lagrangian Trajectory Model. This allows for the effects of emissions, chemistry, deposition and ozone entrainment to calculate a spatially varying ambient background concentration.

Street canyons

'Street canyons' occur when buildings are located adjacent to roads and can lead to elevated pollution levels. An advanced street canyon module has been specifically developed by CERC for ADMS-Urban; this supersedes the simpler approach based on the Danish Operational Street Pollution Model (OSPM, Hertel and Berkowicz, 1990, Hertel at al., 1990).

The advanced street canyon module (Hood et al., 2014) includes the following features:

  • The model has been formulated to consider a wider range of canyon geometries, including the effects of tall canyons and of canyon asymmetry;
  • The concentrations predicted by the model vary with height within the canyon;
  • Emissions may be restricted to a subset of the canyon width so that they are specified only on road carriageway lanes and not on pedestrian areas;
  • There is the option to include consideration of 'network' effects, where pollutants reaching the end of one street canyon can pass into a connected canyon; and
  • Concentrations both inside and outside a particular street canyon are affected when running this model option.

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).

Urban Canopy

The urban canopy module calculates a neighbourhood scale variation of wind speed and turbulence based on gridded values of building height, horizontal and vertical area density. In areas with taller buildings and higher building densities, the near-ground wind speed is reduced and the turbulent intensity is increased. In contrast, areas with lower building heights and densities, such as large urban parks or outlying residential areas, can show increased near-ground wind speed and reduced turbulent intensity. These changes alter the dispersion of pollutants, especially from near-ground sources such as roads.


Users can include the effect of up to 25 dominant buildings on point source emissions. 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.

Road tunnels

ADMS-Urban can calculate the displacement of road traffic emissions from within a road tunnel to the tunnel end. The model creates volume sources outside the tunnel exit portal, optionally following a connected outflow road, with extents depending on wind speed and traffic speed. ADMS-Urban can also represent artificial tunnel ventilation systems which extract traffic pollutants to a separate vent location.

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