ADMS-Urban can be used to examine emissions from 7500 sources simultaneously, including:
Source parameters include:
Up to 500 user-defined emissions profiles can be included in any modelling run to take into account the diurnal variation in traffic flows.
Seasonal variations can also be included with up to 500 monthly profiles.
Variation of sources with wind direction can also be modelled.
For more detailed modelling, up to 500 annual hourly profiles can also be modelled.
A variety of meteorological data can be used for input and the format required is deliberately kept very simple.
Wind speed, wind direction and temperature are required along with cloud cover, heat flux or solar radiation.
The meteorological pre-processor calculates the necessary boundary layer parameters from the user's input.
There are a variety of suppliers of meteorological data across the world. A CERC meteorological data converter can convert METAR and other NWS data to ADMS format.
For road sources, the user can enter hourly speed and traffic flow data into the model and use ADMS-Urban's built-in emission factors or, alternatively, the user can enter pre-calculated emissions data, for example emissions calculated within CERC's Emissions Inventory Toolkit, EMIT, which includes many factors such as current and future factors for Euro standard engines.
Modelling roads in urban areas is more complex than just modelling the emissions from traffic as a line source. Both the effect of street canyons and traffic-induced turbulence are included when roads are modelled in ADMS-Urban.
When modelling any local emissions, it is important to include the background ambient concentrations that are advected from outside the modelling area. Background ambient concentrations can be hourly values, or if these are not available, constant values can be assumed.
In the UK, these background data can be downloaded from the Defra website (http://uk-air.defra.gov.uk/data/) and included directly in any ADMS-Urban modelling scenario.
In urban areas, it is also important to include the aggregated emissions from sources that may be too small to define explicitly, but whose aggregate emissions contribute to overall pollution levels. For example, domestic emissions of NOx from an individual household may not be known, but the aggregated emissions could be calculated using area-wide figures for fuel consumption. In ADMS-Urban, a grid source with up to 3000 grid cells can be included in any run to represent these aggregated emissions.
Pollution concentrations can be calculated for averaging times ranging from seconds up to years. ADMS-Urban can calculate percentiles, the number of exceedences of threshold concentrations and rolling averages. These options allow users to compare concentration results directly with appropriate limits, for example those given by the UK NAQS, US NAAQS, EU or WHO.
Model results are usually first verified by making comparisons with locally monitored data. This can be done by outputting results at receptor points corresponding to monitoring site locations. Modelled and monitored concentrations can then be compared as a time series plot.
Results created by ADMS-Urban are often presented as colour contour plots. The intelligent gridding enables users to model a large area yet obtain high spatial resolution in areas of particular interest—in and around the roads. The ADMS-Urban contour plots are an extremely effective way of communicating results to decision makers, the public and other stakeholders.
Intelligent gridding gives high resolution of results where it is needed—in and around the roads. The three figures below show an area of 1.4 km2 with approximately 5-km length of roads being modelled.
The roads are shown in red and the output points used to create (1) as black dots. Both regular grid points and extra intelligent gridding points inside and either side of the road are shown. The spacing of the intelligent gridding points is related to the width of the road, and the user can vary the along-road spacing.
(1) Concentration results using the intelligent gridding option. The contours reveal the shape of the roads and the high concentrations (i.e. those shown in yellow, orange and red) are fully resolved.
(2) Concentration results using only a regular grid with a resolution of approximately 70 m. Although the locations of the roads can be seen, results are in general very blobby.