Olesen, H.R., Ellermann, T., Christensen, J.H. 2011: Assessment of the impact of alternative regulations of the sulphur content in maritime fuel. National Environmental Research Institute, Aarhus University. 42 pp. – NERI Technical Report No. 818.
In 2009, on behalf of the Danish Environmental Protection Agency, the National Environmental Research Institute at Aarhus University carried out a study to assess the contribution from ships to air pollution in Denmark (Olesen et al., 2009). The study included an assessment of the contribution from ship traffic to the air pollution load for the three years 2007, 2011 and 2020. The computations for the year of 2007 were based on actual data, while computations for the years 2011 and 2020 were based on assumed scenarios for the future emissions from ships and land-based sources.
The current study is an extension of the previous in order to examine certain specific issues in more detail. It is based on the same data, computer models and assumptions. However, the geographical area of interest is extended to comprise Scandinavia and not just Denmark as in the previous study. The level of detail is highest for the region near Denmark.
Several variants of projections for ship emissions are considered for the years between 2011 and 2020. For landbased sources only one set of projections has been used in all calculations, which is the same as used in the previous study. Thus, for land-based sources it has been assumed that new and reduced national emissions ceilings will be adopted in EU for 2020. The negotiations concerning the new emission ceilings have been postponed, and currently it is uncertain how large the future reductions of the land-based emission will be. However, this is not critical to the objective of the current study, which is to examine the effects of certain variations in ship emissions.
The North Sea and the Baltic Sea are appointed Sulphur Emission Control Areas (SECA), where the maximum allowed sulphur content in fuel is reduced over time in a stepwise fashion, according to a set of requirements adopted by the International Maritime Organization, IMO. In 2011 the maximum content of sulphur in heavy fuel is 1%, while in 2020 the maximum level will be 0.1%. Ship owners have the option of implementing alternative measures (scrubbers) if they have similar effect on pollution.
The current study has been carried out on request of the Danish Shipowners Association, who requested an analysis of the impact of certain alternative temporal profiles for the regulation of sulphur content in maritime fuel. The study compares different ways to proceed in the transition from the present level of maximum 1% sulphur in maritime fuel to a maximum level of 0.1% in 2020. All profiles have the same start and end values for sulphur content in respectively 2011 and 2020, but they differ in path for the intermediate time period. The following profiles are considered:
Based on emission inventories for the previous project, but modified to reflect the above profiles, model calculations to assess air pollution concentration levels have been carried out with the model DEHM (Danish Eulerian Hemispheric Model), which describes transport, chemical and physical processes and dispersion of air pollution. DEHM is capable of computing air pollution concentrations for a large number of substances.
The content of sulphur in maritime fuel has an effect on air pollution with sulphur dioxide (SO2) and fine particles (PM2.5). Accordingly, the consequences of the alternative profiles for sulphur regulation have been examined in terms of the concentration levels for sulphur dioxide and fine particles. Adverse health effects are primarily related to PM2.5 concentrations, which are thus of particular interest.
In studies of health effects it is a widely used crude assumption that health outcomes such as the number of lost life years to a first approximation vary linearly with PM2.5 concentrations. It is outside the scope of the current study to carry out complete calculations of the health effects of ship traffic. However, a relative estimate of the health effects of the various scenarios for a specific location can be obtained by comparing time averaged PM2.5 concentrations for the various profiles.
In order to interpret the results it is necessary to know that a distinction is made between various types of fine particles. Primary particles exist as particles immediately after they have left the source; the emission of primary particles decreases somewhat if the sulphur content in fuel is reduced. On the other hand secondary particles were not 'born' as particles, but are created from gases, which undergo chemical transformation during transport – a process that continues for several hours or days after the pollution has left the source. Thus, sulphur dioxide which is emitted from ships will result in the formation of secondary fine particles after a while. However, the formation of secondary particles is a complicated process and many other substances than sulphur dioxide can contribute to the formation of particles. For this reason a substantial reduction in sulphur emission will not necessarily have any great impact on the formation of particles, and it is necessary with comprehensive calculations – as those presented here – to assess the effect of reduced sulphur content in fuel.
Atmospheric dispersion models are only able to describe a part of the particles found in the atmosphere. In order to make this clear we use here the designation mPM2.5 (modelled PM2.5) for the part of fine particles which can be modelled. mPM2.5 includes the primary particles and the secondary inorganic particles. However, it is not possible with customary models to describe the particles which are secondarily formed from organic compounds, and which are, i.a., emitted from vegetation.
The results of calculations for the various profiles can be summarised as follows.
Considered as an average over the ten year period 2011-2020 the two profiles for sulphur regulations Base profile and Balanced profile result in almost identical concentrations for the substances. The main difference is the time development in the trends, were the Balanced profile gives stepwise reductions in 2012 and 2018, while the Base profile gives a single larger reduction in 2015.
The Postponement profile results in slightly larger ten-year average concentrations compared to the Base profile and the Balanced profile. According to the Postponement profile the sulphur content is only reduced to 0.5% in 2015, while the full reduction to 0.1% is postponed to 2020. In the Copenhagen area the effect of the Postponement profile is that the concentration level of fine particles (mPM2.5) will be 0.04 mg/m3 higher than for the Base profile. This difference amounts to 6% of the contribution from ships, or to 0.8% of the contribution from all sources. It should be noted that these values refer to the 'urban background level' in Copenhagen, i.e. at some distance from busy streets. In busy streets the relative contribution from ships will be smaller.
In the Mixed profile 29 specific shipping routes have been assumed to follow the postponement profile (implying 0.5% sulphur from 2015 to 2019), while the remaining fleet follows the accepted regulations. The routes in question were appointed by the Danish Shipowners Association, and are indicated in Appendix A. The average concentrations over the ten year period 2011-2020 lie between those of the Base profile and the Postponement profile. Compared to the total pollution level the differences between the Base profile and the Mixed profile are small, but locally it is possible to distinguish effects on the concentrations due to the higher sulphur content used at some of the shipping routes. For example this can be observed in the area between Rødby and Puttgarden.
In general the differences between the profiles stand out most clearly for concentration levels of SO2, while they are less pronounced for primary PM2.5, and smallest for mPM2.5. This is caused by the fact that SO2 emissions are entirely dependent on sulphur content in fuel and that the ship emissions are a major source of SO2. Formation of primary particles does also depend on sulphur content, but to a smaller extent. The contribution to mPM2.5 from ships is due not only to sulphur emissions, but also to NOX emissions Therefore, changes in fuel sulphur content lead to quite modest changes in mPM2.5.
The share of the concentrations that originate from ship traffic is generally higher for SO2 than for particles. For instance in Copenhagen, about 19% of the total concentrations of SO2 can be attributed to ship traffic, while this is only the case for around 13% of mPM2.5, and only 3% of primary PM2.5. These numbers refer to the average for the period 2011-2020.
The most pronounced difference between the profiles occurs for SO2 in areas with much ship traffic. However, this difference should be seen in light of the low concentrations calculated for SO2. The ten year average of the contribution from ships to SO2 concentration in Copenhagen (about 0.1 mg/m3) is less than 0.1% of the EU limit value for the diurnal concentration (125 mg/m3). Although the averaging times are not comparable this illustrates that the level of concentrations calculated for SO2 is low.
The study shows that there are large spatial variations in the impact of the different scenarios. For the cities considered the largest difference between the scenarios is seen for coastal cities where the ship traffic is dense. The largest variation in health impact due to the different scenarios will therefore be in the major cities with high density ship traffic such as Copenhagen and Gothenburg.
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