This layer provides a Critical Level (CLe) for ammonia against which impacts on a SSSI should be assessed. The value is the lowest CLe for a feature on that site. The layer gives the SSSI name, SSSI code and ammonia Critical Level. The ammonia CLe can be: 1: a 1µg/m3 NH3 Critical Level indicates a SSSI has N-sensitive bryophytes/lichens as a feature or has bryophytes/lichens as key components of a habitat feature of that SSSI; 3: a 3µg/m3 NH3 Critical Level indicates a SSSI has N-sensitive vegetation, or has invertebrate features that are dependent on N-sensitive vegetation; NS: all features on a site are considered not to be particularly sensitive to ammonia; this does not mean that other aspects of a development will not have negative impacts on a SSSI, for example throug
h water pollution or disturbance.