One of the most important advanced modules in ADMS-Urban is the chemistry module. The following options are available:
Other advanced modules are:
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.
In many urban areas, the dominant pollution source is road traffic, and the pollutants usually of major interest are NOx, O3, PM10 and PM2.5.
The ADMS-Urban 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 also predicts changes in ozone concentrations.
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.
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.
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 or downwind from a large emitter of SO2.
'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. The street canyon module included within ADMS-Urban/Roads is based on the Danish Operational Street Pollution Model (OSPM, Hertel and Berkowicz, 1990, Hertel et al., 1990).
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).
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.