Sulphur and nitrogen oxides (SOx and NOx) from ship exhausts are a potentially significant contributor to Ocean Acidification in heavily trafficked areas such as the Baltic Sea. The brackish water of the Baltic Sea has a lower buffer capacity than seawater, and is thus more sensitive to acidification. The maximum sulphur content of marine fuel oil in Emission Control Areas (including the Baltic Sea) will be reduced from 1% to 0.1% in 2015.
Two possibilities are available for commercial shipping: to use expensive low-sulphur fuel, or to use seawater scrubbing systems to absorb acidic gases from the engine exhaust. This second option generates large volumes of acidic seawater, which therefore acidify the water if not neutralised before release. In either case, the consequences of the release for marine organisms are unknown.
Modelling studies include the atmospheric transport and deposition of SOx and NOx (1), the resulting chemical changes in the water (2), and the transport and fate of the acidified water (3). The scenarios that the model calculations are based on will include the extent to which scrubber technology (5) is introduced, and the consequences of scrubber water release for the marine biota will be examined through microbiological experiments (4). The model scenarios are developed in dialogue with a reference group representing the shipping industry and government authorities, which is the Joint Industry Project on Scrubber Installation Challenges within the Zero Vision Tool. A monitoring programme (6) for shipping-derived acidification in the Baltic will be designed. The results of this research will support future policy development for regulation and monitoring of SOx and NOx emissions from shipping.