CERC — Environmental Software and Services

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Comprehensive software for modelling road traffic pollution

Model options

One of the most important advanced modules in ADMS-Roads is the chemistry module. The following options are available:

  • NOxNO2 chemistry
  • Sulphate chemistry

Other advanced modules are:

  • Street canyons
  • Complex terrain

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 effects on observed concentrations.

Chemistry module

NOxNO2 chemistry

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

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.

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).

These reactions have a significant effect on the concentrations of particulates in areas where there are a large number of industrial sources emitting SO2.

Street canyons

'Street canyons' are defined as the deep, narrow, valley-like spaces created when a road is enclosed by tall buildings on both sides. High pollution levels are often observed in street canyons. ADMS-Urban includes two modules for modelling street canyons.

The basic street canyon module is based on the Danish Operational Street Pollution Model (OSPM, Hertel and Berkowicz, 1990, Hertel et al., 1990).

The advanced street canyon module (Hood et al., 2014) can be used if a more detailed model of the street canyon is required. It differs from the basic module in the following ways:

  • 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.

Road tunnels

ADMS-Roads 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-Roads can also represent artificial tunnel ventilation systems which extract traffic pollutants to a separate vent location.

Buildings (ADMS-Roads Extra only)

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

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