The shipping sector is a significant contributor to emissions of air pollutants in marine and coastal regions. In order to
achieve sustainable shipping, primarily through new regulations and techniques, greater knowledge of dispersion and
deposition of air pollutants is required. Regional model calculations of the dispersion and concentration of sulfur,
nitrogen, and particulate matter, as well as deposition of oxidized sulfur and nitrogen from the international maritime
sector in the Baltic Sea and the North Sea, have been made for the years 2011 to 2013. The contribution from shipping is
highest along shipping lanes and near large ports for concentration and dry deposition. Sulfur is the most important
pollutant coupled to shipping. The contribution of both SO
A change in regulation for maximum sulfur content in maritime fuel, in 2015 from 1 to 0.1 %, decreases the atmospheric sulfur concentration and deposition significantly. However, due to costs related to refining, the cleaning of exhausts through scrubbers has become a possible economic solution. Open-loop scrubbers meet the air quality criteria but their consequences for the marine environment are largely unknown. The resulting potential of future acidification in the Baltic Sea, both from atmospheric deposition and from scrubber water along the shipping lanes, based on different assumptions about sulfur content in fuel, scrubber usage, and increased shipping density has been assessed. The increase in deposition for different shipping and scrubber scenarios differs for the basins in the Baltic Sea, with highest potential of acidification in the southern basins with high traffic. The proportion of ocean-acidifying sulfur from ships increases when taking scrubber water into account and the major reason for increasing acidifying nitrogen from ships is increasing ship traffic. Also, with the implementation of emission control for nitrogen, the effect of scrubbers on acidification is evident. This study also generates a database of shipping and scrubber scenarios for atmospheric deposition and scrubber exhaust from the period 2011 to 2050.
Emissions of air pollutants is a large problem; air pollutants have harmful effects on human health, the environment, and buildings. They also influence climate and water quality (Seinfeld and Pandis, 2006; Monks et al., 2009; Fuglestvedt and Berntsen, 2009). There has been a significant decrease in land-based emissions over land areas in Europe since the risks associated with high levels of air pollutants were brought to light 2 decades ago. During the same time, however, emissions from shipping in the Baltic Sea and the North Sea have increased, with the exception of a very recent decrease in sulfur emissions and successive emissions of particulate matter (PM) due to regulations (Gauss et al., 2013; Jonson et al., 2015). Shipping is the most cost-effective option for global transport of goods, and over 90 % of world trade is carried by sea (IMO, 2016). The Baltic Sea area is one of the busiest shipping areas in the world and it is of great importance for the development and economy of the surrounding countries. The intensity of shipping in the Baltic Sea has increased during the last decade and it is expected to increase further in the coming years.
Shipping primarily generates emissions of nitrogen oxides
(
Effects of air pollution vary in both space and time; they may be short-lived and local or more prolonged and global
(Seinfeld and Pandis, 2006). Exposure to PM encompasses a variety of risks to human health, primarily on the
respiratory organs and the cardiovascular system (World Health Organization, 2006). Corbett et al. (2007) estimated that
shipping-related emissions of PM contribute to approximately 60 000 deaths annually on a global scale, with
impacts concentrated to coastal areas along the major trade routes. Further, PM may be absorbing or
reflecting, which has an impact on the Earth's radiation balance. The net effect of emissions from the maritime sector on the
radiation balance is negative, resulting in a cooling effect (Eyring et al., 2005; Fuglestvedt and Berntsen, 2009). Jonson
et al. (2015), hereafter abbreviated J15, estimated that current emissions from shipping in the Baltic Sea region cause
a shortening of life expectancy by 0.1–0.2 years per person in areas close to the main shipping lanes. Exposure to high levels of
sulfur oxides causes health issues such as irritation to the respiratory system, lungs, and eyes (World Health Organization,
2006). High levels of nitrogen in the atmosphere also have negative impacts on human health, cause corrosion of materials, and
are included in the process of degradation of methane (Fuglestvedt and Berntsen, 2009; Eyring et al., 2010). Deposition of
nitrate contributes to both eutrophication and acidification of water and soil. A pH reduction in the ocean causes worsening
conditions in a lot of marine ecosystems (Andersson et al., 2008). Hunter et al. (2011) modelled acidification from strong
acids in the North Sea, Baltic Sea, and South China Sea. On an annual scale the trends were on the order of
The maritime sector was, at least earlier, one of the least controlled sources of anthropogenic emissions. It is a global cross-border sector with conditions making legislation challenging (Van Aardenne et al., 2013). The International Maritime Organization (IMO) is the agency within the United Nations (UN) responsible for maritime security and safety together with prevention of pollutants by ships (IMO, 2016). IMO has formulated the International Convention for the Prevention of Pollution from Ships (MARPOL), which has been ratified globally (CleanShip, 2013). MARPOL and its Annex VI regulate emissions from ships.
The regulations include the Sulphur Emission Control Area (SECA), which consists of the Baltic Sea, North Sea, English Channel, and North America's coastal areas (IMO, 2017; J15). Residual oil or high-sulfur fuel oil (HSFO) can have up to 3.5 % sulfur content, but a global mean estimate is 2.4 % (IMO, 2009) to 2.7 % outside SECA (ENTEC, 2005). In the SECAs a number of reductions have been made. In May 2006 the sulfur content in maritime fuel was restricted to 1.5 % (percentage by mass) by refining to marine gas oil. In 2010, it was reduced to 1.0 % and according to J15, this reduction of sulfur had a positive effect on air quality and the deposition of sulfur. A further reduction of the permitted level of sulfur to 0.1 % was made in January 2015 (Van Aardenne et al., 2013). From 1 January 2020 the upper sulfur content should be reduced to 0.5 % globally (outside the SECAs), even if 2025 is more probable outside the European Union (Jonson et al., 2015). The reduction in SECA has led to extensive investment in scrubbers, or exhaust gas cleaning systems (EGCSs), since the increases in refined oil price. Scrubbers use seawater to remove the sulfur oxides generated from high-sulfur fuels. An expected effect of open-loop scrubbers is that acidification is concentrated along the shipping lanes as the scrubber exhaust is released into the water. With scrubbers the ships can still use HSFO and it seems that the 0.5 % limit can be avoided (S&P Global Platts, 2016).
There is currently no international regulation of direct particulate emissions from shipping. However, with less sulfur,
particle emissions will also decrease, but since there are other sources as well, the decrease is less. The regulations of
nitrogen emissions in MARPOL (TIER) are defined as a function of year of installation and ship speed (IMO, 2007). The TIER I
standard was implemented in 2000 and was 10 % stricter than for ships built before 2000. The introduction of TIER II in
2011 was up to 15 % stricter then the former. As regulations only include newly produced ships, the effects of
regulations of nitrogen emissions from shipping have so far been small. There are also Nitrogen Oxide Emission Control
Areas (NECAs), e.g. in the Caribbean Sea and along the North American coast, but so far, not in the Baltic Sea and North
Sea. However, at the end of 2016 it was decided that in 2021 a NECA will be introduced for the Baltic Sea and North
Sea. There are indications that with this introduction, emissions of
J15 did a thorough study of air pollutants from shipping in the Baltic Sea and the North Sea. They used the European Monitoring and Evaluation Programme (EMEP) model
(Simpson et al., 2012) and estimated the effects of present and future emissions of
The present study is to some extent similar to J15; we study deposition and near-surface concentrations originating from
shipping, also introducing the estimation of the future effects from scrubbers in the Baltic Sea. We use the same chemical
transport model as J15, the EMEP model, although at a lower resolution,
The unified EMEP is policy driven under the Convention on Long-range
Transboundary Air Pollution (CLRTAP) for international co-operation to solve transboundary air pollution problems. The
programme is divided into five centres working with emission inventories, measurements, and chemical and dispersion modelling
(
The EMEP model is considered to be a robust model for dispersion modelling in the atmosphere (Simpson et al., 2012; Gauss
et al., 2015). In Gauss et al. (2015), a comparison of model results from the EMEP model version rv.4.7 and observations of
annual averages of concentrations at individual stations for 2013 was made. On average, sulfur dioxide concentration was
underestimated by 11 %, nitrogen dioxide was underestimated by 7 %,
The meteorological input data used in the EMEP model are from the Integrated Forecast System (IFS), which is a global forecast
model run by the European Centre for Medium-Range Weather Forecasts (ECMWF). Chemical data used in the EMEP model cover 56
persistent and 15 short-lived components, chemical reactions, phase changes, and solubility in water. Emission inputs consist
of gridded yearly national emission data (Vestreng, 2003; Simpson et al., 2012). The anthropogenic emissions are categorized
into 10 different groups called Selected Nomenclature for Sources of Air Pollution (SNAP). All nations in the EMEP area are
responsible for reporting annual gridded emission data for each SNAP sector. National shipping is included in SNAP 8 (other
mobile sources and machinery) and is a part of the emission data that each nation should report. International shipping is
also included in SNAP 8. International ship emission data used in the model were designed according to Table 1. In EMEP model
rv.4.4, ship emissions and their distributions were mainly from the ENTEC/(IIASA) International Institute for Applied Systems Analysis inventory. ENTEC UK Ltd. (now part of AMEC Environment
Infrastructure, UK,
International ship emission data for the different versions of the EMEP model used in this study.
In the development of the data set in EMEP model version rv.4.8, new aspects, such as SECA, the economic situation, and the use of different sizes of ships, have been included. The emission data were designed for 2000 to 2011. In order to supplement emission data for the following years, extrapolation with the Centre on Emission Inventories and Projections (CEIP) method were used. This interpolation was, however, shown to significantly underestimate the 2012 and 2013 emissions in the North Sea and in the Baltic Sea (Fagerli et al., 2015). Emissions from international shipping are assumed to be constant throughout the day and year in the model (Simpson et al., 2012). This was also shown by Jalkanen et al. (2014), with emissions being within 10 % in the years 2006–2009.
Between model versions several changes that affect aerosol production and modelling have been implemented by the EMEP community, e.g. modification of the sea salt parametrization, changes in the standard aerosol surface area and uptake rates, dust boundary conditions, and an update of the split of PM into elemental carbon, organic matter, and the remainder. Furthermore, biogenic emissions of dimethyl sulfide (DMS) have been updated. Rather than being prescribed, DMS emissions are now calculated dynamically during the model calculation and vary with meteorological conditions.
Comparing the emissions in EMEP rv.4.4 and 4.8 shows very small differences, on the order of less than 1 %. However, deposition and concentrations deviate significantly due to the new modifications of the chemistry and physics. Figure 1 shows the relative change in 2011 (%) going from rv.4.4 to 4.8 in deposition (from shipping) of OXS and OXN, respectively. Overall, the deposition has increased but mostly over land, and OXN has increased in the northern Atlantic and OXS has increased north of Great Britain. In the Baltic Sea the increase is minor for OXS, less than 10 %, but for OXN the increase is between 5 and 30 %.
Difference (%) in deposition due to shipping, from EMEP model rv.4.4 to rv.4.8 run for the year 2011 for
Historical ship emission data were taken from the global gridded EDGAR 4.2 data set (Olivier et al., 2011), with a horizontal
resolution of 0.1
For background emissions of
We validated the EMEP modelled data for 2013 using measured concentrations of nitrogen dioxide, sulfur dioxide, and
PM from stations Vavihill and Utö (Fig. 2). Data for Vavihill were downloaded from the database of the
Swedish Environmental Research Institute (
The division of the basins of the Baltic Sea–Skagerrak system. OR: Øresund; GO: Eastern Gotland Basin; AL: Åland Sea; BE: Belt Sea; NW: Northwest Gotland Basin; AS: Archipelago Sea; AR: Arkona Basin; GR: Gulf of Riga; BS: Bothnian Sea; KA: Kattegat; BH: Bornholm Basin; GF: Gulf of Finland; and BB: Bothnian Bay. Dots represent the measuring stations at Vavihill and Utö. The figure is redrawn from Omstedt et al. (2015).
This investigation consists of two parts. A database with historical and future scenarios of emissions and depositions of OXS and OXN (the database) was created. The EMEP model version rv.4.4 was used with meteorology from the years 2009 to 2011 and emissions from 2011 (see Sect. 3.3). In the second part, the model was validated to coastal measurements of concentrations for the year 2013 using the newer model version rv.4.8. As seen in Sect. 2.2, rv.4.8 gives higher depositions of OXS and especially OXN. This is further discussed in Sect. 5. Also, the spatial pattern of concentration and deposition was analysed and compared to the results from J15. For each studied year, two model runs in the EMEP model were made, a base run and a scenario run. In the base run, all emission sources were included, and in the scenario run, the emissions from international shipping in the Baltic Sea and North Sea were excluded (SNAP 8). The scenario run was subtracted from the base run to obtain the impact of the international maritime sector in the Baltic Sea and the North Sea.
PM is difficult to measure and various measuring instruments register different types of particles, which result in some uncertainties to input data. Also, some semi-volatile compounds exist in both gaseous and particle form and the definition of the different particle groups vary in different countries. Moreover, there are still components of the coarser particles, such as aerosol and biogenic organic farming dust that are not included in EMEP model. Another uncertainty of the input data is that not all nations included in the EMEP area report yearly emissions (Gauss et al., 2015). We validated the EMEP modelled data for 2013 using measured concentrations of nitrogen dioxide, sulfur dioxide, and PM from the Vavihill and Utö stations.
Measured data were compared to daily averages of modelled data from the
Five future scenarios differing with respect to the sulfur content of the fuel and scrubber usage of the shipping fleet were
developed (Table 2). Scenario no. 1 corresponds to the fuel content regulation from January 2010 to December 2014 (1 %
sulfur in the fuel), and scenario no. 3 (0.1 % sulfur in the fuel) corresponds to the regulations from January 2015.
Scenario no. 2 has been included since in Sweden it was suggested as an alternative, low-cost reduction in sulfur content
(0.5 % sulfur in the fuel). In scenarios 4 and 5, use of the open-loop wet scrubber technique for removing sulfur from the
exhaust is assumed for 50 and 100 % of the fleet, respectively. The use of scrubbers is assumed to increase linearly from
no scrubber installations at all. The increase rate of the proportion of ships using scrubbers is the same for scenarios 4
and 5 but ends at 50 or 100 %, respectively. Hence, these are similar until 2020. It is assumed that the fuel used
in the ships with scrubbers will have an average low-cost sulfur content of 2.7 %, corresponding to the current average
outside the SECA (ENTEC, 2005). Further, it is assumed that the ships in the basins north of the Baltic, Archipelago,
Åland, and Bothnian seas and Bothnian Bay cannot use the scrubber technique to a large extent. This is due to the ice
properties in the winter and the low alkalinity. For scenarios 4 and 5 the emissions to the atmosphere are estimated to
correspond to 0.1 % sulfur in the fuel (following the regulations). To achieve atmospheric emissions corresponding to
0.1 % sulfur in the fuel, it is assumed that 96 % of the sulfur is taken up in the scrubber, the scrubber water is
untreated and discharged, and the sulfur oxides are directly transformed into strong sulfuric acid. Regulations of nitrogen
oxide emissions are in an early stage. Therefore, these emissions are assumed to increase at the same rate as the shipping
traffic. We here follow the TREMOVE European transport model (De Ceuster et al., 2006), which gives an increase of 2.5 and
3.9 % per year for cargo and passenger traffic, respectively. In addition, the effect of a NECA was studied, following
assumptions made in J15. There is no seasonal variation in ship emissions in the ENTEC/IIASA inventory (2011) and the monthly
variation through the years 2006–2009 presented by Jalkanen et al. (2014) is rather low (
Future scenarios that differ with respect to the sulfur content of the fuel and scrubber usage.
In Omstedt et al. (2015) a database for ship emissions and the corresponding depositions was constructed for the 1900–2011 period using a combination of emission databases (ENTEC/IIASA, EDGAR 4.2, and EDGAR–HYDE 1.3) and deposition from the EMEP model. For the years 2006–2009, the emission distribution was scaled to correspond to that presented by Jalkanen et al. (2014); for 2010, linear interpolation was used. Ship traffic was also assumed to follow the regulated changes in fuel sulfur content in the SECA area. We assume 2.7 % sulfur in the fuel until May 2006, 1.5 % until the end of 2009, and 1 % thereafter. This information was also used to correct the EDGAR 4.2 emission fields. Further back in time, the emission fields from 1900 to 1970 from EDGAR–HYDE 1.3 were used.
Total emissions of
Here we extend the database into the future using the alternative scenarios described in Sect. 3.3. We also use a similar methodology as in Omstedt et al. (2015), with the reference year 2011. The spatial distribution of atmospheric deposition of sulfur oxides and nitrogen oxides from ship traffic was estimated by the EMEP model. The model was first run for the meteorological years 2009 to 2011 with emissions from 2011. The variation in deposition between the three years indicated that the inter-annual effect of meteorology was low for annual deposition. Initial analysis to help find the better method revealed that dry deposition is more focused along ship routes than wet deposition; the dry part of the deposition was thus assumed to be scaled by the local emissions. The wet deposition was more spread. Local ship emissions accounted for approximately 25 % of deposition in the central Baltic Sea and approximately 45 % of wet deposition in the Kattegat. In the Kattegat, almost half of the wet deposition originated from North Sea ship traffic, whereas a very small proportion of the wet deposition in the Baltic Sea east of Bornholm originated from the North Sea. Therefore, the wet deposition trends of sulfur oxides and nitrogen oxides in each basin were set equal to the local emission, except for the Kattegat, Belt Sea, and Øresund, where 50 %, as a first-order approximation, was assumed to depend on emission trends in the North Sea. This approach resulted in a reference year (2011) of deposition-to-emission ratios with a monthly resolution. The relative seasonal variability was kept throughout the period.
Non-ship emission trends follow the RCP 4.5 scenarios from 2010 (Lamarque et al., 2010) and deposition simulations (Engardt and Langner, 2013) using the MATCH model (Robertson et al., 1999). Ship emissions from RCP 4.5 (Eyring et al., 2010), including the traffic distribution from ICOADS (Wang et al., 2008), were replaced by our scenarios described in Table 2. Total emissions were calculated by correspondingly correcting the MATCH output. Last, the spatial fields were averaged into the Baltic Sea basins defined in Fig. 2.
For the deposition scenarios, 2011 is the base year. That means that the relative spatial distribution of ship effects remains the same during the scenarios. Figure 3 shows the ship emissions and spatial distribution of dry, wet, and total deposition in 2011. Even if the ship emissions remain constant throughout the year, the weather causes the deposition pattern to change. In Fig. 4 the seasonal variations (mean of the meteorological years 2009–2011 and emissions from 2011) in the deposition of OXS are shown in six Baltic Sea basins (Kattegat, Arkona, Bornholm, Eastern Gotland, Gulf of Finland, and Bothnian Bay). In most basins there is a minimum during the summer and a maximum in the autumn.
Monthly deposition of oxidized sulfur (OXS) in six basins of the Baltic Sea (defined in Fig. 2).
The ship emission scenarios in the Baltic Sea are shown in Fig. 5. Emissions into the atmosphere (Fig. 5a) all show positive trends after 2015, due to the increasing traffic. With the traffic scenarios, emissions have more than doubled in 2050 compared to 2015. The reduction of sulfur content in fuel will, as expected, result in a reduction in sulfur emissions into the atmosphere in the Baltic Sea area. With scrubbers, the OXS goes directly into the water along the shipping lines. Note that it is assumed that ships are not using scrubbers north of the Baltic Sea proper (as discussed in Sect. 3.3). Averaged over the whole complete Baltic Sea (Fig. 5b), it is seen that, if using 2.7 % sulfur fuel, the input of OXS into the sea surpasses the deposition from the 1 % scenario already by 2020. This is regardless of which scenario (4 or 5) is used. If all ships in the region south of Åland use scrubbers and fuel with a sulfur content of 2.7 %, the emission of sulfur oxides into the Baltic Sea is expected to be almost 3 times the size in 2050, compared to if no scrubbers and fuel with a sulfur content of 1.0 % were used (Fig. 5b).
Total deposition of OXS and OXN in the Baltic Sea (
The deposition scenarios of sulfur from shipping, together with the historical data from Omstedt et al. (2015), are shown in Fig. 6. The deposition of sulfur from ship emissions in the Baltic Sea increased rapidly until the 1970s and then more slowly until 2005 (e.g. Claremar et al., 2013). When applying scenario 2 or 3 the deposition becomes significantly lower. The total deposition of sulfur in the Baltic Sea, from all emission sources, reached its maximum in the second part of the 1900s. It has decreased steadily since then and the deposition of sulfur is expected to continue to be low for the examined time period from present to 2050 (Fig. 7). The contribution of deposition of OXS from shipping is expected to increase somewhat from 2010 to 2050 in all basins of the Baltic Sea, but the levels will stay low. The deposition of sulfur from all emission sources is predicted to be rather invariable from 2010 to 2050, as given from RCP4.5.
Annual ship deposition of sulfur (
Annual deposition of sulfur from all emission sources (
Annual ship deposition of nitrogen (
The deposition in the whole Baltic Sea is presented in Table 3. The ship contribution to the total atmospheric OXS deposition
will decrease, from 18 % in 2011 to 5 % in 2030, and 7 % in 2050 (scenario 4). With scrubbers, the contribution adds up to
more than 50 %. In 2050 the atmospheric deposition will have been reduced from 160 to 95
The deposition of nitrogen from ship emissions is expected to increase in all the basins in the Baltic Sea from present to 2050 as we do not include any coming regulations on nitrogen (Fig. 8). The increase is due to an increase in traffic scenario. The total deposition of nitrogen in the Baltic Sea, from all emission sources, is expected to increase in the Baltic Sea compared to the current deposition level (Fig. 9). The increase in nitrogen deposition varies significantly for the different basins, and for the Kattegat basin the highest values of nitrogen deposition in the 1970s will be exceeded before the year 2050. The contribution of deposition of OXN from shipping is expected to become a more significant contributor to total deposition of OXN from 2010 to 2050 in all basins of the Baltic Sea (Table 3). The OXN deposition is significantly lower than in J15. They used the EC4MACS Interim Assessment (Amann et al., 2011), which indicates that the RCP 4.5 has a lower scenario for nitrogen. This means that if using EC4MACS data, the OXN deposition from shipping would be smaller, but the total effect would be larger.
Emissions from shipping in the Baltic Sea (
The deposition for OXN in the whole Baltic Sea is presented in Table 3. The ship contribution to total increases for the
atmospheric deposition, from 35 % in 2011 to 60 % in 2030 and 72 % in 2050. In 2050 the atmospheric deposition
has been increased from 77 to 88
Annual deposition of nitrogen from all emission sources (
Annual proton input from OXS and OXN in six basins of the Baltic Sea (defined in Fig. 2) for the years 2010 to 2050. The red
line corresponds with shipping scenario 3 and the magenta and cyan lines correspond with shipping scenarios 4 and 5, respectively
(scrubber
We have, so far, not accounted for the long-term shift to TIER II and TIER III in the NECA. The decision to create a NECA in the Baltic Sea
and North Sea was made while preparing this paper. TIER II was introduced in 2011 and TIER III will be introduced in
2021. In Table 4, estimates from J15 are shown and a reduction of emissions of 26 % in the Baltic Sea and 29 % in the North
Sea can be concluded in 2030, relative to emissions without a NECA, i.e. to ships mainly following TIER II. We apply
a reducing factor to our deposition due to both TIER II implementation and the establishment of a NECA in 2021. We assume that half of the fleet will have implemented
each regulation after 10 years and will have completely implemented regulations after 30 years. This yields power curves with an exponent of 1.7 as long as
there are not more than three concurrent fleets. Further, we assume that TIER I was completely implemented in 2012 and that
the implementation for TIER I will be replaced by TIER II until 2021, when TIER III takes over. Hence, in the period 2021–2031
when all TIER fleets will be present, the TIER II fleet will remain constant at 50 % until 2031 when TIER III will reach
50 %. After that, TIER II is the only remainder in the TIER III fleet and decreases accordingly. The estimated fleet parts are presented in
Fig. 10a. The ship emissions of
The deposition of OXS and OXN together acts as a strong acid in the water. The result is an acidifying effect and a pH
decrease (Fig. 11). At pH 8, a proton input of 1
The difference in physics in EMEP model rv.4.4 and 4.8 causes different deposition. With the assumption that rv.4.8 better
represents the reality, a correction was calculated for the Baltic Sea basins. The result is shown in Fig. 12 for OXS and
OXN. It is seen that for OXS the difference is below 5 %, with a decreasing trend counting from the Kattegat to the Bothnian
Bay. The pattern for OXN is almost the opposite, with the largest correction in the northern parts. Also, the correction is
higher, 10 to 30 %. The impact on the future scenarios is discussed in the next section. Due to the limited correction for
sulfur deposition and the low values in comparison to scrubber exhaust, we neglect this correction. The nitrogen is more important,
although the largest relative effect of the correction is in the Bothnian Bay,
where the deposition is smallest, just 50
Correction of deposition caused by ship traffic in the different Baltic Sea basins.
The spatial distribution of the emission from international shipping in the Baltic and North seas in 2011 (from the EMEP model) is demonstrated in Fig. 3a. The emission distribution (relative) is almost the same in 2013. The highest emission levels of the pollutant are found near big ports and shipping lanes, especially in the area around the English Channel and Denmark. Compared to ship emissions in 2011, there is a decrease in the inventory used for the EMEP model (Table 4). There has been a decrease, although not stepwise, as if all ships were using 1 % sulfur in fuel, directly. This may be an effect of the interpolation as mentioned in Sect. 2.3 (Fagerli et al., 2015), i.e. an underestimation of the real ship emissions in 2012 and 2013. In Table 4 the emissions used in J15 are also shown. There are sometimes large differences, which are possibly an effect of the resolution of data and Baltic Sea basin areas. The largest deviation is for the North Sea, but this area is not directly analysed in the present investigation.
The evaluation of the EMEP model concentrations (with rv.4.8) in 2013 is summarized in Figs. A1 and A2 and Table A1 in the
Appendix. The yearly averages of the measured and modelled concentrations of the pollutants were rather consistent
(Table A1). The EMEP model underestimates the concentrations of
The seasonal variability in modelled and measured concentrations at Vavihill and Utö in 2013 is shown as monthly averages
in Fig. A2. There is overall good agreement for most of the pollutants. However,
WHO guidelines for the annual average exposure for
Annual mean concentration in 2011 of near-surface concentration (at 3
Percentage (%) of the total surface concentration, caused by international shipping in the Baltic Sea and the North Sea in 2011.
International shipping in the Baltic Sea and the North Sea contributed significantly to total surface concentration of
nitrogen oxides, sulfur dioxide, and PM from 2009 to 2013. In some areas in the Baltic Sea region, the
contribution of nitric oxide, nitrogen dioxide, and sulfur dioxide from international shipping represents up to 80 % of
the total concentration of the pollutants from all emission sources in 2013. For
Concentration of
Deposition of OXN caused by shipping.
Percentage (%) of the deposition caused by international shipping in the Baltic Sea and the North Sea in 2013
of
The simulated (by EMEP rv.4.8) wet deposition, in 2013, from shipping in the Baltic Sea and North Sea reaches over
60
International shipping in the Baltic Sea and North Sea contributed significantly to the deposition of OXS and OXN from 2009 to 2013. In 2013, the percentage contribution from the shipping to the total cumulative wet deposition of sulfur from all emission sources reached 29 % in some areas of the Baltic Sea region and the contribution of dry deposition of sulfur is calculated to a maximum of 84 % of total dry deposition of sulfur in Fig. 17. The percentage contribution of wet deposition of nitrogen reaches a maximum of 28 % and the contribution of dry deposition of nitrogen reached a maximum of 47 %. Contribution of ship emissions to the total (wet and dry) annual deposition of sulfur is as much as 56 % in some areas and 29 % for nitrogen. The deposition pattern for the dry and wet deposition of OXS and OXN differs slightly when wet deposition is spread over a larger area than dry deposition. Dry deposition is more focused along ship routes. Conversely, dry deposition of the pollutants caused by shipping represents a higher percentage of the total amounts of the deposition than the wet deposition from shipping. The percentage contribution of dry deposition from shipping is higher for OXS than OXN.
In this investigation we have focused on the impact from scrubbers on sulfur deposition in the future, its potential
acidification of the Baltic Sea, and in addition also included OXN. We have not taken into account input from
non-sea-salt base cations, like calcium from cement industry and ammonium from agriculture. Trends in those may
alter acidification. For instance, calcium emissions have decreased, at least in the 1990s and 2000s (e.g. Claremar
et al., 2013). Similar deposition scenarios were used in Turner et al. (2017), but here reduced
This modelling study was based on international shipping emissions, which means that the contribution of emissions from all shipping, including national, in the Baltic Sea and North Sea is somewhat higher than these results show. In further work it would be of interest to include national emissions. To obtain more robust results and to reduce uncertainties in the model, national reported input data should be put under more control and a future study should also examine how much impact it has on the results that several countries do not give complete reports of their annual emissions.
In this investigation we used a mixture of modelling and statistics, with all their uncertainties. We used constant
meteorology in the future scenario, but limited the uncertainties by using the average of three meteorological years
(2009–2011). However, in order to obtain more robust results, a study over a longer period of time is required, using the best case
meteorology for every year. The resolution of the model,
The new regulation of permitted weight percentage of sulfur in marine fuel was introduced in January 2015, which makes it of interest to include 2015 and the following years in further studies to analyse the outcome of the new regulation. The 2015 0.1 % limit was implemented in the scenarios but the compliance and the traffic scenarios on the longer timescale remain to be validated. In further studies, it would also be of interest to include a validation study of the deposition of the pollutants. Scenarios are based on assumptions on shipping activities as well as fuel use and cleaning patterns. Alternative fuel or cleaning techniques might be developed, giving alternative scenarios.
To identify the dispersion of the different components of PM from shipping, it would be of interest to model each component separately. Stricter regulations of sulfur content in maritime fuel and increased use of other fuels will result in a new mixture of PM from shipping. This ongoing change of composition of the pollutants makes it of interest to understand the dispersion of each separate component. In further studies a better resolution of the model is recommended to be used to examine the impact on a local level. No seasonal variations have been taken into account in this study. Results of the study of J15 demonstrate that emissions from international shipping vary to some extent over the year. The seasonal cycle of acidifying deposition is of importance for the surface water due to the biological cycle and stratification of the water, as seen in Omstedt et al. (2015).
Model calculations using the chemical transport model EMEP show that the shipping in the Baltic Sea and North Sea is an
important source of high near-surface concentrations of nitric oxide, nitrogen dioxide, sulfur dioxide, and
particulate
matter and deposition of OXN and OXS in the Baltic Sea and North Sea area. The highest concentrations of
the pollutants were found near big ports and along shipping lanes. There, the international shipping in the Baltic Sea and
North Sea was responsible for up to 80 % of near-surface concentrations of nitric oxide, nitrogen dioxide, and sulfur
dioxide in 2013. For
Future scenarios of ship emissions and the use of open-loop scrubbers were combined with modelled deposition from ships and other sources, forming scenarios of acid deposition in the Baltic Sea basins. The impact of the different scenarios differs slightly for the different basins in the Baltic Sea, with the highest acidification in the southern basins. The scrubbers focus the sulfur along the shipping lanes. The ship part of acidifying ocean deposition increases for sulfur when including the scrubber water and for nitrogen oxides due to increasing ship traffic. Direct acidification of ocean deposition from shipping increases for sulfur when including open-loop scrubbers. The impact is even larger for the Baltic Sea as a whole since almost all sulfur goes into the water and not to the surrounding land areas. The estimates of the reduction in OXN deposition from introducing a NECA in 2021 showed that there may be a large reduction of acidification. However, in relation to the worst-case scenario with 100 % scrubbers in 2050, this effect is minor.
Considering the negative effects of the air pollutants studied and as the pollutants are a contributing factor of several current challenges in the Baltic Sea and North Sea area, this study shows that continued analysis of the maritime sector is required in order to achieve sustainable shipping in the Baltic Sea and North Sea. For the marine environment, the large-scale usage of open-loop scrubbers should be avoided, at least with the use of residual oil.
To conclude,
open-loop scrubbers concentrate sulfur input along shipping lines, with enhanced potential for acidification, even if
the atmospheric deposition is estimated to be low; acidification from a fleet with 100 % scrubbers, using high-sulfur-content fuel, may reach the total deposition
levels along the shipping lanes from the 1970s to 1990s; open-loop scrubbers will contribute significantly to the marine environment, unless medium-sulfur-content
distillates are used.
Deposition data used and produced in this work are available
at Environment Climate Data Sweden (ECDS). The historical data are found in
Claremar and Rutgersson (2017b) at
Comparison of model daily concentration average results from the EMEP model and measured data for 2013 at Utö and Vavihill. Obs: observed data; Mod: modelled data; Corr: correlation coefficient; and RMSE: root mean square error.
Scatter plots of model results vs. measured data of daily average concentrations of
Measured and modelled monthly average of concentrations of the pollutants at Vavihill and Utö in 2013. The red line corresponded to concentrations of the EMEP modelling and the blue line showed measured concentrations.
The authors declare that they have no conflict of interest.
This article is part of the special issue “Multiple drivers for Earth system changes in the Baltic Sea region”. It is a result of the 1st Baltic Earth Conference, Nida, Lithuania, 13–17 June 2016.
This work is part of the Swedish Research Council Formas programme “Commercial shipping as a source of acidification in the Baltic Sea (SHIpH)”, contract no. 2012–2120. The SHIpH group is acknowledged for valuable discussion concerning the traffic and scrubber scenarios, as well as scenario definitions. It is also part of the “Baltic Earth – Earth System Sciences for the Baltic Sea Region” programme. Magnuz Engardt at SMHI is thanked for the MATCH model deposition output. EMEP/MSC-W is acknowledged for the EMEP model code and input data. The EMEP model computations were performed using resources provided by SNIC via the Uppsala Multidisciplinary Center for Advanced Computational Science (UPPMAX) under projects snic2014-1-75 and snic2015-6-139. Edited by: Marcus Reckermann Reviewed by: two anonymous referees