The Norwegian Ministry of Environment started the programme on Tolerance Levels in Nature in 1989. A working group with representatives from the Directorate for Nature Management (DN) and Norwegian Pollution Control Authority (SFT) is administrating the programme.
Estimated total yearly depositions for the period 1997-2001 were approximately 79 000 tonnes sulphur and 146 000 tonnes nitrogen. Compared with similar estimates for the period 1992-1996, there has been a reduction in the sulphur and nitrogen deposition of 32% and 4% respectively. In 1978-1982 the corresponding numbers were 191 000 tonnes sulphur and 173 000 tonnes nitrogen.
Also the amounts of precipitation varied significantly between the different periods with 10% lower amounts during the period 1978-82, 6% higher amounts during 1988-92 and 6% lower amounts during the period 1992-1996 compared to 1997-2001. However, changes in precipitation amounts can only to a small extent explain the observed changes in deposition of sulphur and nitrogen.