Why does APIS say to seek site specific advice?

Critical loads and levels have been established for many habitats and are based on the best available information. However, for some habitats a variety of site specific factors can influence how much of certain air pollutant concentrations or deposition might presents a risk to their function. As such, there may be insufficient information to assign a critical level or load to all types of habitat on that specific site. In these cases, APIS advises to seek site specific information from the relevant authority (eg conservation agency or site manager).