Standardized naming convention and classification system for critical loads of nitrogen and sulfur deposition.

Critical loads (CLs) of atmospheric deposition have been used for multiple decades to assess the impacts of air pollutants on terrestrial and aquatic ecosystems. However, these CLs have been developed by different researchers, at different times, using different methods, and are named in different ways with varying levels of information and levels of specificity. In this study, we identified the elements that describe CLs and used them to develop and test a standardized CL naming convention and a complementary CL classification system applicable to all CLs. The CL naming convention consists of: the form of deposition; the biological receptor, response, and threshold; and chemical criterion and threshold, thereby clearly communicating what the CL is and what it protects. The CL classification system contains all the elements that define and describe a CL, but the CL classes are not fixed and are therefore, defined by the user. The application of the CL naming convention and classification system to an existing US CL database and national forest was successful, demonstrating not only the utility of the naming convention and classification system, but how both can also be used to guide future CL science.