The data provide critical loads of acidity, and of nutrient nitrogen for the distributions of UK habitats sensitive to acidification and/or eutrophication. Critical loads have been calculated and applied to UK natural and semi-natural habitats sensitive to acidification and/or eutrophication (excess nitrogen as a nutrient). Critical loads data are available for these habitat types at 1x1 km resolution for the UK. In addition, acidity critical loads are available for 1752 selected freshwater sites throughout the UK. Critical loads are defined as the maximum pollutant load (of acid or nitrogen deposition) that a sensitive element of the environment (e.g., soils, vegetation) can tolerate without adverse harmful effects occurring, according to present knowledge. Habitat distributions are defined from a combination of CEH Land Cover Map 2000 and a number of ancillary data sets (e.g., species distributions, altitude, soils), used to further refine their distributions. It should be noted that the habitat distributions maps and areas provided here and used for UK critical loads research for Defra (a) only include areas where data exist for the calculation or derivation of critical loads; (b) may differ from other national habitat distribution maps or estimates of habitat areas. This may also result in a difference in the total habitat areas mapped for acidity and for nutrient nitrogen critical loads. The data have been generated under numerous Defra-funded contracts that brought together UK experts on the impacts of air pollution on UK habitats. The acidity critical loads data were last revised in 2004 and the nutrient nitrogen critical loads data were updated in 2011. The data are based on methods agreed at national and international meetings and workshops held under the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP). Full details about this dataset can be found at https://doi.org/10.5285/299e2779-0787-46bb-9482-03ad474eae27

This data resource consists of two files: (a) 1x1 km resolution Average Accumulated Exceedance (AAE) data summarising the exceedances of acidity critical loads for eight habitats; (b) 1x1 km resolution AAE data summarising the exceedances of nutrient nitrogen critical loads for thirteen habitats. The data provide information on the amount of excess acid or nitrogen deposition above the critical load values set to protect acid- and nitrogen-sensitive habitats in the UK. The AAE has been calculated using UK 5x5 km Concentration Based Estimated Deposition (CBED) data for 2013-15 - https://doi.org/10.5285/fd8151e9-0ee2-4dfa-a254-470c9bb9bc1e . The data were generated under Defra-funded work to assess the potential areas of acid and nitrogen sensitive habitats at risk of adverse impacts from excess atmospheric acid and nitrogen deposition. Reducing the area and amount of critical load exceedance continues to be a driver of Government policy on reducing emissions of acidic and nitrogen-containing air pollutants (sulphur dioxide, nitrogen oxides and ammonia). Full details about this dataset can be found at https://doi.org/10.5285/e32745d2-fb56-4f91-a235-6b213a8b45cb

This dataset contains the linkages between designated features and their relevant critical loads or levels. The designated features come from the UK network of protected nature sites including: (i) Special Areas of Conservation (SAC) (ii) Special Protection Areas (SPA) (iii) Sites of Special Scientific Interest (SSSI) - England, Scotland, Wales (iv) Areas of Special Scientific Interest (ASSI) - Northern Ireland. Critical loads and levels are set under the auspices of the United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution. For nutrient nitrogen critical loads are based on empirical evidence, mainly observations from experiments and targeted gradient studies. These empirical critical loads are assigned to habitat classes of the European Nature Information System (EUNIS) to enable consistency of habitat terminology and understanding across Europe. In order to assign the relevant critical load to Annex I features, A/SSSI habitat features, or habitats of Annex II/SPA features, habitat correspondence tables are used to determine the relationship between the EUNIS classes for which nitrogen critical loads are set and the interest features. Critical loads of acidity are based on soil and habitat types. They are set for six Broad Habitats; acid grassland, calcareous grassland, dwarf shrub heath, bogs, montane, unmanaged coniferous and broadleaved woodland. Critical Levels for air pollutants are not habitat specific and have been set to cover broad vegetation types (e.g. forest arable, semi-natural), often with critical values set for sensitive lichens and bryophytes. They have been derived from experiments and observation that show varied effects on vegetation including visible injury symptoms of exposure and species composition changes in semi-natural vegetation. Full details about this dataset can be found at https://doi.org/10.5285/95139a35-8880-4a17-86e4-5eb2f54073c4