Substances favouring the eutrophication process on reaching bodies of surface water. These gases are principally:

• Sulphur oxides (SO_X): Total of sulphur dioxide (SO₂) and sulphur trioxide (SO₃) expressed as mass units (kg) of SO₂
• Ammonia (NH₃): Expressed in mass units (kg)
• Nitrogen Oxides (NO_X): Sum of compounds resulting from the combination of Nitrogen with Oxygen, fundamentally nitrous oxide (N₂O) and nitric oxide (NO), expressed as mass units (Kg) of NO