International Maritime Organisation introduced new regulations to limit air pollutants caused by shipping. Emission Control Zones (ECA) require that ships use low-sulfur fuel on the sea. These rules reduce sulphur and nitrogen oxide emissions, which contribute to the direct radiative forcing.
The new rules will come into force on 1 January 2020. The ECA stipulates that ships must use fuel oils with a sulphur limit of less than 0.1%. Ports outside the ECA have national restrictions which require the use of low-sulfur ship fuel. The UK played a key role in these initiatives, including cosponsoring designation of the North Sea an ECA.
Sulphur and NOx emissions from shipping can be reduced by burning low-sulphur fuel and using exhaust gas cleaning systems, or scrubbers, onboard vessels. These systems spray water into exhaust gases to remove pollutants and sulphur oxide before they are released in the air. The washwater is then thrown overboard.
These technologies can also be combined with conventional fuels. They are available in a variety of forms. The choice of which technology to install will be a decision made by individual companies and their customers, and it will depend on the specific conditions in their ports and the local availability of low-sulphur fuels.
The implementation of a global sulfur cap led to a dramatic drop in shipping emission. However, the spatial distribution of SO2 pollution remains similar to that without the new standards (Supplementary Fig. 1). This is partly due to the fact the new regulations were introduced when oil prices were relatively low. The impact of this on transport costs, and the necessary modal switch for compliance was reduced.
In addition, the global sulfur cap has not yet had an effect on shipping's total nitrous oxide (NOx) emissions, as most of NOx comes from land-based sources.
In 2019, we compared SO2 and no2 levels using satellite data derived from the Tropospheric Monitoring System (TROPOMI), Sentinel 5, in European waterways. The temporal analyses focused on assessing impacts of global sulfur caps which entered into force in 2010 and European NOx ECAs (Environmental Control Areas) that became operational in 2012.
Satellite data reveal that SO2 vertical-column density (VCD), which is a measure of air pollution, is much lower in North Sea ECA. However there are not obvious differences in comparisons between levels of BA Quadripartite Joint Responsibility and Bay of Biscay. The spatial analysis also shows NO2 concentrations to have remained fairly stable over the studied time period.
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