Ammonia Emission Dispersion Modelling
Guidance on Ammonia Emission Dispersion Modelling and SCAIL calculation.
Initial model
Initial model used for Screening: SCAIL (Simple Calculation of Atmospheric Impact Limits)
SCAIL is a simple online screening tool that can be used to estimate the effect of an agricultural emission (e.g. poultry shed) on a habitat (e.g. ASSI). This estimate may then be used to determine the exceedance or non-exceedance of the habitat's impact limit and will help users in deciding whether more detailed modelling or site specific investigation is required.
Information required
| Information | Detail |
|---|---|
| Source Location | Easting and Northing |
| Source Type | Housing, litter/manure storage, land spreading |
| Ventilation Type | Naturally ventilated or force ventilated |
| Building Height | Metres |
| Livestock Number | Number of animals |
| Housing Floor Area | Square metres |
| Type | Broilers, layers etc |
| Fan Location | Roof or side of building |
| Number Of Fans | Number |
| Fan Diameter | Metres |
| Fan Flowrate | M3/s |
| Designated Site Details | Detail |
| Search Radius | Kilometres |
| User Specified Site | Detail |
| Site Name | Name of site |
| Site Location | Easting and Northing |
| Habitat Within Site | Acid grassland, bog etc |
Use the APIS website (Air Pollution Information System) to identify the Critical Level of each sensitive species/habitat: It is important to distinguish between a critical load and a critical level. The critical load relates to the quantity of pollutant deposited from air to the ground, whereas the critical level is the gaseous concentration of a pollutant in the air. (For more detail on Critical Loads/Levels visit the Air Pollution Information System website.
More detailed dispersion modelling
More detailed dispersion modelling could be provided by the following models:
ADMS
ADMS is a dispersion model used to model the air quality impact of existing and proposed industrial installations. It has been developed by Cambridge Environmental Research Consultants (CERC) in collaboration with government bodies.
The model predicts wet and dry deposition using meteorological data and typography.
It covers dispersion from point, area, volume and line sources with a straight-line plume trajectory from source to receptor or grid point.
Concentrations are modelled on an hour by hour basis using an appropriate regional meteorological data set.
This modelling software is the industry standard in the United Kingdom.
AERMOD
AERMOD is another dispersion modelling software package which was produced by American Meteorological Society/United States Environmental Protection Agency.
It is a steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.
Further guidance
NIEA (2015) 'Guidance for Operators on producing an Air Dispersion Modelling Report for a PPC Farming Application' will provide more detail on the type of information required when published.