Provenance & quality
The Air Pollution Information System (APIS), through the 'Site Relevant Critical Loads' tool, provides critical loads for acidity and nitrogen and critical levels for ammonia, sulphur dioxide and nitrogen oxides for designated features within every SAC, SPA or A/SSSI in the UK. In addition, deposition and concentration data for nitrogen and sulphur pollutants are provided at each site to give an estimate of critical load/level exceedance.
The data provided is based on pollutant deposition gridded maps for nitrogen and acid deposition and concentration maps of ammonia, nitrogen oxides and sulphur, which are overlayed to a GIS shape file of site boundaries in the UK (e.g. SAC, SPA, SSSI). These gridded maps were then clipped to provide the pollutant values for each grid square including the area of the clipped grid. The resulting data was then queried to generate site statistics in the form of a minimum, maximum and area weighted average values for each of the pollutants.
For nitrogen and acid deposition values and ammonia concentrations, 3 year average pollutant maps were used at a resolution of 5 x 5 km from the CBED model for the years 2013-2015. For nitrogen dioxide and sulphur dioxide concentrations the 1 x 1 km PCM model was used based on the 3 year average (2013-2015). Deposition values are generated for specific habitat types (forest and semi-natural) to be used in critical load exceedance calculations.
The full methodology is available in the contextual metadata linked to this record.
The work of APIS is jointly funded between the Centre for Ecology & Hydrology and the UK pollution and conservation agencies including Natural Resources Wales (NRW), the Environment Agency, Northern Ireland Environment Agency, Natural England, the Joint Nature Conservation Committee (JNCC), the Scottish Environment Protection Agency (SEPA), and Scottish Natural Heritage (SNH).