Cambridge Environmental Research Consultants (CERC)

- Industrial Air Pollution Modelling Software

From

ADMS 5 is an advanced dispersion model used to model the air quality impact of existing and proposed industrial installations. Its many features include allowance for the impacts of buildings, complex terrain, coastlines and variations in surface roughness; dry and wet deposition; NOx chemistry schemes; short term releases (puffs); calculation of fluctuations of concentration on short timescales, odours and condensed plume visibility; and allowance for radioactive decay including γ-ray dose.

  • assessment of modelled air pollution concentrations against air quality standards and limit values including those from WHO, EU, UK, USA and China
  • planning/permitting under IED/EPR,
  • stack height determination,
  • odour modelling,
  • environmental impact assessments and
  • safety and emergency planning.

The dispersion model ADMS 5 is currently used in many countries worldwide. Users of ADMS 5 include:

  • over 130 individual company licence holders in the United Kingdom,
  • regulatory authorities including the UK Health and Safety Executive (HSE),
  • Environment Agency in England and Wales,
  • Scottish Environmental Protection Agency (SEPA) in Scotland,
  • Northern Ireland Environment Agency (NIEA) in Northern Ireland,
  • government organisations including the Food Standards Agency (United Kingdom),
  • users in other European countries, Asia, Australia, North America and the Middle East.

ADMS 5 is a new generation Gaussian plume air dispersion model, which means that the atmospheric boundary layer properties are characterised by two parameters:

  • the boundary layer depth, and
  • the Monin-Obukhov length

rather than in terms of the single parameter Pasquill-Gifford class.

Dispersion under convective meteorological conditions uses a skewed Gaussian concentration distribution (shown by validation studies to be a better representation than a symmetrical Gaussian expression).

Model options: ADMS 5 has a number of model options including: dry and wet deposition; NOx chemistry; impacts of hills, variable roughness, buildings and coastlines; puffs; fluctuations; odours; radioactivity decay (and γ-ray dose); condensed plume visibility; time varying sources and inclusion of background concentrations.

Meteorological pre-processor: ADMS 5 has an in-built meteorological pre-processor that allows flexible input meteorological data both standard and more specialist. Hourly sequential and statistical data can be processed, and all input and output meteorological variables are written to a file after processing.

User-defined outputs: The user defines the pollutant, averaging time (which may be an annual average or a shorter period), which percentiles and exceedence values to calculate, whether a rolling average is required or not and the output units. The output options are designed to be flexible to cater for the variety of air quality limits, which can vary from country to country, and are subject to revision.

Visualisation: ADMS 5 includes the ADMS Mapper: an integrated mapping tool for displaying and editing source data, buildings and receptor locations and viewing results. The model has links to the Surfer contour-plotting package, in addition to ArcGIS and MapInfo Professional Geographical Information System (GIS) software. The GIS links can be used to enter and display input data, and display output, usually as colour contour plots.

Terrain converter: Utilities are available for creating terrain files for Britain, France, Northern Ireland and Republic of Ireland.

Plume rise, buoyancy and momentum
ADMS 5 uses a Runge-Kutta method to solve the conservation equations to estimate plume rise. This allows greater scope to include advanced model options than Briggs empirical expression used in other Gaussian type models. The ADMS 5 method takes into account the effect of plume buoyancy and momentum, and includes the penetration of boundary layer inversions.

Dry and wet deposition
The rate of dry and wet deposition to the ground can be modelled in ADMS 5. Dry deposition is assumed to be proportional to the near-surface concentration, and deposition velocities can either be entered by the user, or estimated by the model. Wet deposition is modelled through a washout coefficient; irreversible uptake is assumed, and plume strength following wet deposition decreases with downwind distance. There is also an advanced option for wet deposition for SO2 and HCl using the falling drop method.

Plumes or puffs
ADMS 5 can model both continuous releases, i.e. plumes, in addition to instantaneous and time-dependent releases, i.e. puffs.

Time varying emissions
Emission rates from industrial sources are rarely constant. The variation of the emission rate with time can be modelled in ADMS 5, in addition to corresponding variations in emission temperature, volume flow rate (or exit velocity), source diameter, and plume water content.

Dispersion Around Buildings
The building effects module in ADMS 5 includes the following features.

Up to 25 buildings can be included in each model run with a Main Building being defined for each source. For each wind direction, a single effective wind-aligned building is defined, around which the flow is modelled.

The flow field consists of a recirculating region (or cavity), with a diminishing turbulent wake downstream.

Concentrations within the cavity, CR, are uniform, and based on the fraction of the release that is entrained. The concentration at a point further downwind is the sum of contributions from two plumes: a ground-based plume from the recirculating flow region and an elevated plume from the non-entrained remainder. The concentration and deposition are set to zero within the user-defined buildings.

Odours
Odours are becoming an increasingly important issue in areas where industrial sites are located close to residential areas. The dispersion of odours can modelled using ADMS 5. Odour release rates and concentrations can be specified/calculated in two types of odour units: ou, which are defined in the form of a ratio, and ouE which are a mass measure.

Fluctuations
ADMS 5 is the only regulatory model of its kind to model short time scale fluctuations allowing the calculation of the probability distributions of pollutant concentrations, probabilities of exceedence of specified threshold, and the range of concentration for averaging time as little as a second. The module has application where estimates of the occurrence of peaks of concentration over short averaging times are important (e.g. odours, 15 minute air quality objective for SO2. This module takes into account variations due both to turbulence, and changes in meteorology.

Plume visibility
The plume visibility module uses the initial water content of the release and the humidity of the ambient air to determine whether the plume will be visible at each downstream distance. The effect of water on the plume density and the heating and cooling effects of condensation and evaporation are taken into account.

NOx chemistry
A simple NOx chemistry scheme is included in ADMS 5, involving the conversion of nitrogen dioxide (NO2) to nitrous oxide (NO) and ozone (O3) in daylight:

3 NO2 + hν → 3 NO + O3

(where hν = ultra-violet radiation), and a reverse reaction:

NO + O3 → NO2 + O2

that occurs both day and night.

Amine chemistry
An advanced model option allows for chemical reactions of amine to form nitramines and nitrosamines. The module has been developed as a consequence of emerging technologies for Carbon Capture and Storage (CCS) some of which are based on amine extraction of CO2.

Radioactive decay and γ-ray dose
ADMS 5 includes a radioactivity module that predicts the decay of radioactive species released from a source. Users may enter up to 10 parent isotopes in any model run, and up to 50 isotopes (parents and daughters) will be output. Half-lives of over 800 isotopes are included in the model and ADMS 5 can also calculate the associated levels of γ-ray dose.

Dispersion in coastal areas


For air dispersion modelling in coastal areas, ADMS 5 includes a coastline module that may be invoked when the following conditions are satisfied:

  • the sea is colder than the land;
  • there are convective meteorological conditions on land;
  • there is an onshore wind.

Flow over Complex Terrain
ADMS 5 uses CERC's complex terrain model, FLOWSTAR, to calculate the flow and turbulence fields that are then used to enhance the calculation of dispersion.

The model predicts a three-dimensional flow and turbulence field over the region of interest, dependent on both input values of terrain height and roughness, as well as the local meteorological conditions.

In ADMS 5, the plume is subjected to these varying flow and turbulence fields, which results in ground level concentrations that may be higher or lower than the corresponding predictions for flat terrain.

It is recommended that the complex terrain option in ADMS 5 be used in regions where the gradient exceeds 1:10, but is less than about 1:3.

Impact of wind turbines on dispersion
The model can allow for the effect on dispersion of one or more horizontal-axis three-bladed wind turbines in the neighbourhood of an emission source.

Link to AERMOD
There is a facility to run the main options of AERMOD to allow the option of using the AERMET meteorological processor.

Emissions Sources

ADMS 5 can be used to assess the effect of emissions from a number of industrial source types:

  • Point source e.g. emissions from a stack or vent.
  • Area source e.g. evaporative emissions from a tank.
  • Line source e.g.emissions from a conveyor belt at a quarry.
  • Volume source e.g. fugitive emissions.
  • Jet source (directional releases) e.g. emissions from a ruptured pipe.

The maximum number of sources that can be modelled in ADMS 5 is 300. Of these up to 300 may be point or jet sources, and within the limit of 300 up to 30 line sources, 30 area sources and 30 volume sources may be modelled simultaneously.

ADMS 5 uses a built-in mapper for helping to manipulate the emissions data (see the Visualisation tools page for more information).

Meteorological Data

Meteorological data is available in ADMS format from a number of suppliers. The advanced ADMS meteorological pre-processor determines the structure of the atmospheric boundary layer based on the input data. Hourly sequential or statistical meteorological data may be input.

Background Concentrations

Hourly sequential or averaged concentrations of background pollutants may be included if required.

ADMS can give output for up to 10 pollutants in one run, which may be either long-term statistical output or short-term output for each hour or meteorological condition in the input meteorological data. Rolling averages, exceedences and percentile statistics may also be calculated.

Output is given on a grid of receptor points covering a specified area and/or at specific receptor locations. Gridded results can be contoured using the ADMS Mapper or one of the included links: Surfer, ArcGIS or MapInfo (see the Visualisation tools page for more information).

Where only a single point source is modelled, ADMS 5 produces output containing detailed plume characteristics, such as plume centreline concentration, plume height, plume spread, etc., which can be graphed using the included ADMS Line Plotter.

Where hills are modelled, there is an option to output the FLOWSTAR flow field, which can be contoured using the included ADMS Vector Plotter.

Other individual model options produce specific model outputs; for full details see the model documentation.

The model interface is designed so that the user can enter the data required for the modelling in as straightforward a way as possible.

The interface consists of several main screens. To set up a model run, the user simply works through the screens entering the relevant data or referencing external data files.

The ADMS 5 model was developed by CERC, with some of the model options written in collaboration with other research organisations, such as the UK Meteorological Office, University of Surrey, and National Power (now Innogy). The model has been comprehensively verified. A number of verification papers are available for download from the Model validation page.

ADMS 5 is supplied with an in-depth user guide (see the User guides page) that details all user inputs and outputs, and includes a number of step-by-step worked examples.

Full details of the technical specification of ADMS 5 can either be found in the Technical specifications page or on requestfrom CERC.

An annual maintenance contract provides support for users; this includes:

  • maintenance model upgrades,
  • use of the helpdesk by e-mail, phone, fax or post,
  • attendance at the annual user group meetings,
  • newsletter twice a year, and
  • access to the password-protected user area.