The concept of “critical loads” refers to the threshold levels of pollutants or stressors that an ecosystem can tolerate without experiencing significant harm or degradation. When the input of these stressors exceeds the critical load (“exceedance”), the ecosystem may experience biological damage. Critical loads are particularly important for understanding how atmospheric deposition may impact ecological health and for informing policy decisions aimed at environmental protection and sustainability. In a special study, the steady-state Simple Mass Balance model was applied to terrestrial ecosystems across Canada to produce nation-wide maps of critical loads of acidity (represented by maps of maximum sulphur critical loads, CLmaxS; maximum nitrogen critical loads, CLmaxN; and minimum nitrogen critical loads, CLminN) and nutrient nitrogen (CLnutN). The maps are provided on a 250 m grid across all provinces and territories for natural and semi-natural terrestrial ecosystems across Canada (excluding organic soils, agricultural areas, and the Hudson Plains ecozone).