As a result from different onboard combustion and energy transformation processes, remarkably for propulsion and energy production, ships represent sources of different substances to the atmosphere. Sulphur Oxides (SOx), nitrogen oxides (NOx), particulate matter (PM) and carbon dioxide (CO2) are emitted to the atmosphere as a direct result. Collectively, ship generated emissions can be significant in areas subject to heavy marine traffic leading to concerns regarding air quality, bot at local level, in coastal areas, or in a more global level, regarding to CO2 emissions leading to Greenhouse Gas emissions and contributing to global warming. Many actions have however been undertaken in recent years to significantly reduce air emissions from ships. Most of these actions have been taken through Annex VI of MARPOL, an international instrument developed through the International Maritime Organization (IMO) that establishes legally-binding international standards to regulate specific emissions and discharges generated by ships.
The table below presents a brief reference summary of the two different air emission categories that can be considered in relation to shipborne combustion processes, either for propulsion power, electrical production or other auxiliary systems.
Having described briefly above the two main groups where Air Emissions can be classified, it is moreover important to mention that sustainable shipping development implies that these shall be dealt with the understanding that a given measure designed to reduce one group of air emissions should not represent a detrimental effect on the other, and vice-versa.
At the EU Level, the Sulphur Directive has been, in a consistent manner with that international instrument, the reference for control of sulphur oxide emissions from ships, regulating the sulphur content in fuels used onboard ships and, with regards to CO2 emissions from ships, the MRV Regulation sets the EU-wide legal framework for the monitoring, reporting and verification of CO2 emissions and other relevant information from maritime transport.