The project was funded by the Joint Nature Conservation Committee (JNCC) and carried out by a team made up of Air Quality Consultants Ltd, the UK Centre of Ecology and Hydrology (CEH), Rothamsted Research, Aether, Lancaster University, and Manchester Metropolitan University.
Critical levels and critical loads, which have been set to protect sensitive ecological features, are currently exceeded in many parts of the UK. The project forecast how this might change by 2030 and beyond. It then considered whether additional improvements might best be achieved by targeting specific emissions sources close to the designated habitats, or whether further national-level emissions reductions would be more cost effective.
The results showed that achieving the UK-wide emissions reductions targets, which are set under the National Emissions Ceiling Regulations, will deliver an overall reduction in nitrogen deposition to priority habitats of 17% by 2030. There will, however, continue to be significant exceedances of the critical levels and critical loads across much of the UK beyond 2030.
Targeting measures on localised zones surrounding each sensitive site (e.g. each Site of Special Scientific Interest (SSSI)) will be almost as effective in reducing nitrogen deposition as applying further national-level emissions reductions, but will cost less. Those targeted measures that will be most effective will depend on which sources contribute most to a site. For example, targeting transport emissions would achieve little to reduce nitrogen deposition to a remote site which is well away from any roads but surrounded by agriculture. Similarly, targeting local agricultural emissions would not drive improvements where road traffic is the dominant local source of nitrogen deposition.
The work highlighted the importance of spatial averaging when determining effects. National-level modelling (on a 5 km x 5 km or 1 km x 1 km basis) might mask exceedances of the critical levels or critical loads close to emissions sources (for example near to roads). Similarly, different mitigation measures might be required to drive improvements to the worst-case locations than would be suggested by coarse, national-scale models. This highlights the importance of local-scale assessment where there are emissions sources very close to a site.
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