This spreadsheet is the underlying data for the biodiversity indicator B5a, Air pollution.
The air pollutants - sulphur dioxide, nitrogen oxides and ammonia - can contribute to acidification, and nitrogen oxides and ammonia can contribute to terrestrial eutrophication. Both problems can adversely affect semi-natural ecosystems. Exceeding the critical load for acid deposition may have direct effects, for example by altering the soil pH and therefore the range of associated species, or indirect effects, for example by increasing dissolved aluminium concentrations in soil and water. Excess nitrogen as a nutrient can lead to leakage of nitrogen from soil systems, causing eutrophication of inland waters, or affect species composition, for example by triggering accelerated growth of some species at the expense of others.
Critical loads are thresholds above which significant harmful effects occur on sensitive UK habitats. Approximately 78,000km2 of terrestrial habitat is sensitive to acid deposition. About 73,000km2 is sensitive to eutrophication; much of this is sensitive to both.
This is one of a suite of 24 UK biodiversity indicators published by JNCC on behalf of Defra; the latest publication date was 19 January 2016 - for indicator B5a the latest data are for 2012. The supporting technical document details the methodology used to create the indicator.