Simple Calculation of Atmospheric Impact Levels (SCAIL) – Combustion

May 2010



  1. Under the Integrated Pollution Prevention and Control (IPPC) Directive, permits are required for combustion installations with a rated thermal input exceeding 50MW. The Directive has been transposed into the Pollution Prevention and Control (Scotland) Regulations 2000, the Pollution Prevention and Control Regulations (Northern Ireland) 2003 and the Environmental Permitting (England and Wales) Regulations 2007, and in the national legislation permits are required for combustion installations with a rated thermal input exceeding 20MW.

  2. Applications for permits need to be assessed for their potential impacts on the environment including the impact of concentrations and deposition downwind of the installation.

  3. There is a clear need for a simple model that could be used for „screening‟ the applications to determine if the environmental impacts are likely to be a problem or not. This simple model provides an estimate of the potential deposition and air concentrations at nearby conservation (receptor) sites, from which a decision could be made whether complex dispersion and deposition modelling is needed.

  4. SCAIL-Agriculture (Simple Calculation of Atmospheric Impact Limits; previously Simple Calculation of Ammonia Impact Limits, SCAIL V2.0) was developed as such a screening tool for assessing the impact of agricultural ammonia emissions.

  5. SCAIL-Combustion has been developed as a partner model to SCAIL-Agriculture as a screening tool for assessing the impact of small to medium scale combustion installations (20-50MW). However, the model has been validated using much larger power stations and therefore could be used as a screening tool for any sized power station.

Meteorological Data

  1. Meteorological data were collected from 78 meteorological stations across the UK. A methodology to calculate the typical metrological year from continuous five-year datasets was developed as well as a geo-statistical procedure to reduce the number of meteorological stations (to 30), whilst maintaining the spatial variability of conditions across the UK.

  2. The nearest meteorological station to the emission point is selected by the screening tool.

Parameterisation of SCAIL-Combustion

  1. SCAIL-Combustion uses a version of the AERMOD modelling software to calculate the dispersion of the combustion installation plume.

  2. Despite the project focus being on relatively small combustion plant, the project uses atmospheric dispersion modelling methods that are applicable to a wide range of different point sources.

  3. The concentration predictions of SCAIL-Combustion generally agree well with detailed modelling using AERMOD and ADMS and also measurements where monitoring data are available. In one case there was not good agreement and this was found to be due to local meteorology differing from the nearest meteorological station selected by SCAIL-Combustion.

  4. SCAIL-Combustion provides a best estimate of concentrations, therefore an additional output of “Worst Case” concentrations and deposition is also calculated by the model to put a conservative upper limit on the impact, which is useful for screening purposes.

Incorporation of SCAIL v2.0 onto the Internet

  1. SCAIL-Combustion can be accessed on the internet via the SCAIL homepage. The online version of the model provides a user friendly interface with an online help system to guide the user through the operation of the model. Both SCAIL-Agriculture and SCAIL-Combustion can be accessed at:

Key words: Combustion, habitat, tool, model, air, deposition

Copies of this report are available from the Foundation, in electronic format on CDRom at £20.00 + VAT or hard copy at £35.00, less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website