Until recently, exhaust emissions from the marine sector were often overlooked. However as other sources of pollution have gradually been reduced, attention has turned to emissions from ships, ferries, boats and barges, especially in ports or inland waterways. The large size of the engines involved is one important factor behind this shift, with another being the intensive use to which they are often subjected. The increased availability of low sulphur fuels has widened the choice of exhaust gas after-treatment systems for both main engines and marine generators.
Since regulations are generally related to the location where they are operated, marine engines tend not to have any exhaust-gas aftertreatment systems fitted as standard. This means that they are prime markets for retro-fitting, whether they are new or in-use.
The International Maritime Organisation (IMO) is responsible for regulating emissions from ships and sets NOx limits which apply in designated Emission Control Areas. National and local regulations also apply in many areas.
Even where there are no regulations requiring emissions reduction, some owners still want to reduce them anyway, either to minimise their environmental impact, or in some cases to make their vessel a more pleasant place to be. This is often the case with cruise ships or superyachts, where passengers can have their experience spoiled by exhaust fumes.