ADMS-Roads

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:

• NO_x – NO₂ 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

NO_x – NO₂ chemistry

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

The NO_x chemical reactions take place over a relatively short time period and in order to get accurate predictions of NO₂ concentrations, NO_x 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 the deep, narrow, valley-like spaces created when a road is enclosed by tall buildings on both sides. Pollution can become trapped in a street canyon, leading to poor air quality.

ADMS-Roads models this effect using an advanced street canyon module, specifically developed by CERC (Hood et al., 2014), which includes the following features:

• Consideration of a wide range of canyon geometries, including the effects of tall canyons and of canyon asymmetry;
• Modelling of the spatial variation of concentration within the canyon;
• The ability to restrict emissions to a subset of the canyon width so that they are specified only on road carriageway lanes and not on pedestrian areas;
• The option to include consideration of 'network' effects, where pollutants reaching the end of one street canyon can pass into a connected canyon; and
• Calculation of the effects on concentrations both inside and outside the street canyon.

The Mapper's 'Canyon and canopy' tool can be used to generate the additional input data required by the module from road network geometry and 3D buildings data.

ADMS-Roads also includes a simpler street canyon module based on the Danish Operational Street Pollution Model (OSPM).

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 Package B and C only)

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