WRF and EMEP4UK domains.The EMEP4UK model framework consists of an atmospheric chemistry transport model (ACTM) which simulates hourly to annual average atmospheric composition and deposition of various pollutants and the weather research and forecast model (WRF). Pollutants simulated include PM10, PM2.5, secondary organic aerosols (SOA), elemental carbon (EC), secondary inorganic aerosols (SIA), SO2, NH3, NOx, and O3. Dry and wet deposition of pollutants are also calculated by the model. WRF is used to calculate the required meteorological input data for the ACTM.

EMEP4UK operates at horizontal resolutions ranging from 50 to 1km by 1km covering the UK and Europe in a one-way nesting approach. A typical model domain setup is shown in the image on the right. The coarse outer European domain is modelled at a horizontal resolution of 50km by 50km, an intermediate domain at a resolution 10km by 10km and an inner domain over the British Isles at a horizontal resolution of 5km by 5km. The outer domain is used at the boundary condition for the intermediate domain and the intermediate domain as the boundary conditions for the inner domain. The model setup is very flexible and can be changed for utilisation in scientific and/or policy applications, for example to contain a more detailed 1km by 1km horizontal resolution domain over a specific area.

The default vertical domain ranges from ~90 m (thickness of the first layer at the surface) up to ~16 km (at the top of the vertical domain), however since version rv4.4 of the EMEP4UK model, setting flexible vertical resolution is possible. The output data shown on the website are from rv4.4, although, a new rv4.6 is available which includes a thin lower surface layer of 50m instead of the previous default of 90m.

The default chemical scheme is the EmChem09 as it has be extensively validated at the European scale. It has 72 species and 137 reactions. Details of this scheme and the others available can be found in the publication Simpson et al. 2012.

Two types of emissions are present in the model: anthropogenic and natural. Anthropogenic emissions of NOx, NH3, SO2, primary PM2.5, primary PMcoarse (the difference between PM10 and PM2.5), CO, and non-methane volatile organic compounds (NMVOC) are included from different sources at respective spatial resolutions. For the UK, emissions values are taken from the National Atmospheric Emission Inventory (NAEI ) at 1 km x 1 km resolution and aggregated to 5 km x 5 km resolution. For the rest of the European domain, the model uses the EMEP 50 km x 50 km resolution emission estimates provided by the EMEP Centre for Emission Inventories and Projections (CEIP ). Emissions estimates for international shipping (ENTEC, 2010) are aggregated to 5 km x 5 km for those emissions within the British Isles domain. Forest fires are also included in the model, as well as biogenic emissions of isoprene and (when required) monoterpenes, which are calculated in the model for every grid-cell, and at every model time-step, using near-surface air temperature.