Critical Loads

Dr Jane Hall

The critical loads concept is an effects-based approach to developing pollutant-abatement strategies. Critical loads defines the pollutant level below which harmful effects on certain elements of the environment are not expected to occur according to present knowledge. 

Critical loads are used as an effects-based tool for assessing the sensitivity of terrestrial and freshwater habitats to the harmful effects of sulphur and nitrogen deposition. By comparing the critical loads with atmospheric deposition (e.g. from rainfall or airborne particles), and determining the excess deposition above the critical load (ie, the "exceedance"), the potential impacts of current and future deposition scenarios are examined. This information is used to help guide and formulate policies that define the emission abatements of sulphur and nitrogen required to protect sensitive habitats across Europe. 

To date, critical loads of acidity and eutrophication have been adopted in the development of national (e.g., Defra’s Air Quality Strategy) and international (eg, Protocols of the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP)) policies. The critical loads concept is also being developed for heavy metals.  For further information follow the links below: