Sea vessels can also be equipped with SCR system in order to reduce NOx emissions in the air. In this case the system utilizes a solution of Urea at 40%, similar to the one used in stationary plants. Thanks to SCR technology the polluting agents released in the atmosphere by ships and vessels can be dramatically reduced.
Naval engines can be retrofitted thanks to compact SCR systems, equipped with a special honeycomb catalyst.
NOx emission limits for marine engines are regulated by the IMO (International Maritime Organization). Tier III will be effective on january 1st 2016, with a reduction of 80% compared to Tier I.