CERC — Environmental Software and Services

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World leading software for urban air quality management

Model input data

Emissions sources

ADMS-Urban can be used to examine emissions from 7500 sources simultaneously, including:

  • Road traffic, over 145,000 roads links (3000 road sources each with up to 50 vertices).
  • Industrial sources, up to 1500 point, line, area or volume sources.
  • Aggregated sources (grid source), up to 3000 grid cells can be used to model emissions from sources that are too small to define explicitly, for example, emissions from domestic housing.

Source parameters include:

  • source location data,
  • road widths and canyon heights for road sources,
  • stack heights, diameters, exit velocities, etc., for industrial sources,
  • grid dimensions for aggregated emissions data.
Example emissions profiles image

Emissions profiles

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 monthly profiles. Variation of sources with wind direction can also be modelled. For more detailed modelling, annual hourly profiles can also be modelled. Time variation emissions profiles can be defined for individual pollutants.

Example wind rose image

Meteorological data

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.

Traffic flow

Sketch of traffic flow in street canyon

Schematic of basic canyon model in ADMS-Urban

Sketch of advanced canyon

Schematic of advanced canyon modelling in ADMS-Urban, combining up to six different dispersion conponents.

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. Advanced street canyon modelling requires an additional data file containing canyon geometry information for each side of the road.

ADMS-Urban can model the ‘blocking’ effect of elevated road carriageways, which prevent downwards dispersion of emissions within the carriageway. Road tunnels can also be modelled, with emissions automatically moved from the tunnel road to outside the tunnel exit portal and/or a ventilation stack.

Background ambient concentrations

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.

Aggregated emissions

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.

Model output data[top]

Example time series image

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.

Source-oriented gridding

Results created by ADMS-Urban are often presented as colour contour plots. Source-oriented 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.

Why do you need source-oriented gridding?

Source-oriented 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.

  • (1) shows concentration results using the source-oriented gridding option, and
  • (2) shows concentration results without the source-oriented gridding option—this type of output is typical of other roads models that do not have the source-oriented gridding option.
Image of output points with intelligent gridding

The roads are shown in red and the output points used to create (1) as black dots. Both regular grid points and extra source-oriented gridding points inside and either side of the road are shown. The spacing of the source-oriented gridding points is related to the width of the road, and the user can vary the along-road spacing.

Image of results with intelligent gridding

(1) Concentration results using the source-oriented 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.

Image of results without intelligent gridding

(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.

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