Scoping report on the potential impact of on-board desulphurisation on the water quality in SOx emission control areas

• Main Authors: Stips, A, Bolding, K, Macias, DM, Bruggeman, J, Coughlan, C
• Format: Report
• Language: English
• Published: Joint Research Centre (European Commission) 2016
• Subjects: Chemistry; Marine Sciences; Oceanography; Ocean acidification
• Online Access: http://plymsea.ac.uk/id/eprint/9015/; http://plymsea.ac.uk/id/eprint/9015/1/LBNA27886ENN.en%20%281%29.pdf

The input of acid substances (like SO2) into the sea has been recognized as an environmental issue that needs to be considered in terms of ocean acidification; acid inputs and techniques to deal with them have implications for member states' obligations under the Water Framework Directive and Marine Strategy Framework Directive. This study provides an initial assessment on the potential impact of on-board desulphurisation equipment (open loop scrubbers) on the seawater quality with focus on SOx Emission Control Areas (SECAs). The study focuses on the potential impact of shipborne SO2 on acidification (pH) of seawater in comparison to the impact from climate change. The report comprises a literature study and a dedicated modelling exercise covering the North Sea region. Most available studies and the peer reviewed literature found only a small additional impact from SO2 emissions on acidification in the various investigated parts of the world ocean. However these studies generally assessed spatially averaged effects and regional and coastal oriented studies are mostly lacking from the literature, which means that potential effects to vulnerable ecosystems in such areas have not previously been considered. A coupled hydrodynamic-chemistry model was employed to assess the impact of adding SO2 and CO2 on the complex carbonate system in sea water. The impact on the pH decrease in the open North Sea region from discharging the acid wash water into the seawater was found to be small, but not insignificant, and regionally varying. The calculated annual mean decrease of pH due to SO2 injection for the North Sea total water column is 0.00011; when considering only the change in the surface layer (0-20m), the annual decrease is 0.00024. The total annual impact from increasing atmospheric CO2 concentrations on the acidification of the North Sea surface area is about 8 times stronger (0.001) than the impact from wash water injection. However because of the pronounced spatial variations the mean impact does not reflect the ...