Licences issued to industrial enterprises are intended to ensure that emissions are gradually reduced. This has been the most important means of reducing Norwegian sulphur emissions. Use of market forces. In Norway, the tax on mineral oil has been used as an instrument to reduce sulphur emissions by making part of it dependent on the sulphur content of the oil. Unlike emissions of gases that threaten to enhance the greenhouse effect, acid emissions can be eliminated almost completely, although it is more difficult to remove NOX than SO2.
Many methods are available, some preventive and some remedial.
Purification of fuel. Before combustion, up to 35 per cent of the sulphur content of coal and oil can be removed by chemical washing. Sulphur dioxide can be removed from waste gases formed by the combustion of coal or oil by adding lime or other chemicals that absorb SO2. Ammonia can also be added to reduce NOX emissions. Sulphur is removed after combustion of the coal or oil by means of various types of filters.