ADMS 5 include the following options:
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.
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.
ADMS 5 can model both continuous releases, i.e. plumes, in addition to instantaneous and time-dependent releases, i.e. puffs.
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.
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 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.
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.
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.
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.
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.
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.
For air dispersion modelling in coastal areas, ADMS 5 includes a coastline module that may be invoked when the following conditions are satisfied:
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.
There is a facility to run the main options of AERMOD to allow the option of using the AERMET meteorological processor. The latest version of AERMOD (12345) is included.
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.