DOI: 10.5285/65ab44a0-58bd-43ab-a3bc-a850ddd9a0f1
title: Deposition and concentration of nitrogen and sulphur for protected sites in the UK, 2017-2019

description: This dataset provides values of sulphur and nitrogen deposition, deposition of non-marine base cations and concentration values for ammonia (NH3), sulphur dioxide (SO2) and nitrogen oxide (NOx) on the UK nature conservation protected sites, averaged over the years 2017 to 2019. The dataset also includes calculated minimum, maximum and gridded average values for each site. Protected nature sites covered are: 
 (i) Special Areas of Conservation (SAC) 
 (ii) Special Protection Areas (SPA) 
 (iii) Sites of Special Scientific Interest (SSSI). 

The data consist of values of nitrogen and acid deposition, non-marine base cation deposition, and concentrations of ammonia (NH3) based on the Concentration Based Estimated Deposition (CBED), and concentrations of NOx and SO2 using the Pollution Climate Mapping (PCM) model. 
Nitrogen and acid deposition data is also given for specific habitat types including: 
 (i) moorland/short vegetation everywhere, 
 (ii) forest everywhere, and 
 (iii) the grid square average over multiple land cover types (i.e. arable, grassland, forest, moorland, urban) 

These habitat-specific data are recommended for use with critical loads for the calculation of critical load exceedances using the relevant deposition/habitat type.
description: The Air Pollution Information System (APIS), through the 'Site Relevant Critical Loads' tool and APIS new mapping interface, 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, sulphur pollutants and non-marine base cations 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, sulphur and non-marine base cations, 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, base cations deposition 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 2017-2019. For nitrogen dioxide and sulphur dioxide concentrations the 1 x 1 km PCM model was used based on the 3 year average (2017-2019). 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).