Development of site relevant critical loads for APIS
ER04
June 2011

Executive Summary

Background to research

Project ER04 is the culmination of three phases of work undertaken over the last four years and includes: the generation of new deposition datasets for 2005 and 2020 with source attribution, the addition of A/SSSI sites, revised critical loads for nutrient nitrogen (2010) and acidity (2004) and the redevelopment of the Site Relevant Critical Loads tool for the APIS website.

Objectives of research

The key objectives of the project were to:

1. Develop, test and deliver an online interactive interface for presenting site-relevant critical loads and providing deposition and source attribution data for UK SACs, SPAs and SSSIs/ASSIs.
2. Update the existing “Search by Source” on APIS, which allows the user to look up a pollution source and the top 50 sites to which it contributes in terms of critical loads exceedance for acidification and nutrient nitrogen.

Key activities

A user survey of the existing tool showed that in general the current tool was very useful for assessing critical loads at user specific sites, but that the functionality and guidance were key areas to be addressed in the new system. These were summarised and are outlined below:

• A better, less cluttered, results page
• Improved graphics
• The ability to rank features by sensitivity in the 'select a feature' select box
• Better guidance on use and interpretation
• More transparency of source/emissions data

Designated features were assessed for their sensitivity to acidification and eutrophication at each site and were linked to critical loads. Six broad habitats for acidity were used in the assignment of critical loads of acidity (acid grassland, calcareous grassland, dwarf shrub heath, bog, montane, unmanaged coniferous and broadleaved woodland). Critical loads of acidity for these habitat classes were mapped for the whole of the UK at a resolution of 1 km. Empirical critical loads for nitrogen were based on the revised 2010 Noordwijkerhout workshop and allocated according to habitat type.

The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) was applied to assess the magnitude and spatial distribution of individual deposition footprints of sulphur and nitrogen associated with gaseous emissions from 156 different point sources and background sources. The analysis was performed for a recent emissions year (2005) and for the UEP30 future emissions scenario year (2020). The 156 emissions sources considered in the study included:

• SO₂ and NO_x emissions from 100 individual point sources
• SO₂ and NO_x emissions from eight background emissions sectors
• Three NH₃ emissions sectors: livestock, fertiliser, and non-agricultural
• Emissions from international shipping
• Long-range transport from European and background sources

A revised database structure was developed to take account of the addition of the A/SSSI sites and the new linkages. New deposition year tables were created. Existing tables (e.g. EUNIS classification, Nitrogen and acidity critical load tables) were updated.

The interface was re-designed making use of PHP and Ajax coding to provide a more user-friendly navigation experience for the user. The wizard type navigation based on the current system was retained but improved. Tabbed content was introduced to handle the Results page so users could easily obtain the information without unnecessary cluster and scrolling.

Extra steps were inserted to handle A/SSSI features so the user could make sensible selections of their habitat before the results page was reached.

The “Search by Source” tool was revised to include the top 50 most affected interest features at a site in the UK for a chosen source. These could be filtered by nitrogen or acidity sensitivity.

Testing was carried out by individuals from the Technical Advisory Group and others in the agencies. System bugs were fixed and re-tested in-house. Any changes to the look and feel of the interface were also implemented.

An online User Guide was produced together with four online tutorials providing a walkthrough and guidance on using the new system.

Keywords: Air pollution, Nitrogen deposition, Acid deposition, Critical Loads, Natura 2000, SSSI, Atmospheric modelling.

Copies of this report are available from the Foundation, in electronic format on CDRom at £20.00 + VAT or hard copy at £15.00, less 20% to FWR members.