DOI: 10.5285/8e7644fe-9f17-4fc3-8e4e-8b10a42d5d50
title: Deposition of nitrogen, sulphur and base cations to the UK (1986-2012)

description: These datasets provide Concentration Based Estimated Deposition (CBED) values of nitrogen, sulphur and base cations deposition for 5x5 kilometre (km) grid squares of the UK averaged over the years 1986 to 2012.

The data consist of deposition values for sulphur, oxidised nitrogen and reduced nitrogen, and base cations. Total deposition is the sum of four components calculated separately: wet deposition, dry deposition of gases, dry deposition of particulate matter and cloud droplet deposition.

Habitat-specific data are provided for (i) moorland/short vegetation, and (ii) forest. Additionally, the grid square average over multiple land cover types (i.e. arable, grassland, forest, moorland, urban) is also calculated. The habitat-specific data are recommended for use with critical loads for the calculation of critical load exceedances. The work in generating and compiling the dataset has been funded by the UK Centre for Ecology & Hydrology (UKCEH) and various Department for Environment, Food & Rural Affairs (Defra) contracts. 
description: The Concentration Based Estimated Deposition (CBED) methodology generates 5x5 km resolution maps of wet and dry deposition of sulphur, oxidised and reduced nitrogen, and base cations from measured concentrations of gases and particulate matter in air and measured concentrations of ions in precipitation. These data are collected at sites in the UK Eutrophying and Acidifying Pollutants (UKEAP) network. The site-based measurements are first interpolated to generate maps of concentrations for the UK. The ion concentrations in precipitation are combined with an annual precipitation map from the UK Meteorological Office to generate values of wet deposition. Gas and particulate matter concentration maps are combined with spatially distributed estimates of habitat-specific deposition velocities to generate dry deposition for 5 land cover categories: forest, moorland, grassland, arable and urban. The deposition to the 5 land cover categories are combined, depending on the relative proportions of different land cover categories in the 5x5 km grid square, to generate values for grid square averaged deposition. Dry deposition includes deposition of gases (Sulphur Dioxide (SO2), Nitric Acid (HNO3), Nitrogen Dioxide (NO2) and Ammonia (NH3) and particulate matter (sulphate, nitrate, ammonium, calcium and magnesium) to vegetation. 

The CBED model was originally written in Genstat, but has been re-implemented in R.  The data provided here come from the R version, which have some small numerical differences from the Genstat version.  The differences arise from differences in the algorithm for spatial interpoolation (kriging), and using the long-term mean orographic enhancement factor in each grid square (rather than recalculating this each year). In earlier years, some components such as aerosols were not measured, which makes the retrospective estimation total nitrogen and suphur deposition incomplete. These components have therefore been estimated retrospectively, based on the long-term mean fraction that each component contributes, compared to the wet deposition (which has the longest measurement record).