Any substance which, if introduced into the sea or atmosphere, is liable to create hazards to human health, ecosystems, or marine life, to damage amenities, or to interfere with other legitimate uses of the sea, (IMO).
Exhaust emissions from marine diesel comprise nitrogen, oxygen, carbon dioxide (CO2), carbon monoxide (CO), oxides of sulphur (SOx), nitrogen oxides (NOx), particulates, water vapour and smoke. Oxides of nitrogen and sulphur are of deep concern as the threat to human health, vegetation and the environment.
Annex VI of MARPOL 73/78 defines requirements for control of emissions from ships.