Effects of strengthening the Baltic Sea ECA regulations

Emissions of most land based air pollutants in western Europe have decreased in the last decades. Over the same period emissions from shipping have also decreased, but with large differences depending on species and sea area. At sea, sulphur emissions in the SECAs (Sulphur Emission Control Areas) have decreased following the implementation of a 0.1% limit on sulphur in marine fuels from 2015. In Europe the North Sea and the Baltic Sea are designated as SECAs by the International 5 maritime Organisation (IMO). Model calculations assuming present (2016) and future (2030) emissions have been made with the regional scale EMEP model covering Europe and the sea areas surrounding Europe including the North Atlantic east of 30 degrees west. The main focus in this paper is on the effects of ship emissions from the Baltic Sea. To reduce the influence of meteorological variability, all model calculations are presented as averages for 3 meteorological years (2014, 2015, 2016). For the Baltic Sea, model 10 calculations have also been made with higher sulphur emissions representative of year 2014 emissions. From Baltic Sea shipping the largest effects are calculated for NO2 in air, but effects are also seen for PM2.5 and depositions of oxidised nitrogen, mainly in coastal zones close to the main shipping lanes. As a result country averaged contributions from ships are small for large countries that extend far inland like Germany and Poland, and larger for smaller countries like Denmark and the Baltic states Estonia, Latvia and Lithuania, where ship emissions are among the largest contributors to concentrations 15 and depositions of anthropogenic origin. Following the implementations of stricter SECA regulations, sulphur emissions from ships in the Baltic Sea shipping now have virtually no effects on PM2.5 concentrations and sulphur depositions in the Baltic Sea region. Following the expected reductions in European emissions, model calculated NO2 and PM2.5 concentrations, depositions of oxidised nitrogen, and partially also surface ozone levels, in the Baltic Sea region are expected to decrease in the next decade. 20 Parts of these reductions are caused by reductions in the Baltic Sea ship emissions mainly as a result of the Baltic Sea being defined as a Nitrogen Emission Control Area from 2021.


Introduction
Even though emissions of most air pollutants have decreased in the countries surrounding the Baltic Sea (BAS) in past decades (Tista et al., 2018), air pollution and atmospheric depositions affecting ecosystems remain a problem in the region. Significant 25 contributions to the emissions also come from shipping, both inside and outside the region. Obtaining reliable data on emissions these regulations only apply to new ships or when major modifications are made on existing ships. Furthermore, from 2020 a global cap on sulphur content in marine fuels of 0.5% will be implemented.
The global effects of international shipping on air pollution and depositions have been discussed in several papers (Corbett et al., 2007;Endresen et al., 2003;Eyring et al., 2007;Sofiev et al., 2018). In a global model calculation Jonson et al. (2018) found that a large portion of the anthropogenic contributions to air pollution and nitrogen depositions in adjacent countries 15 could be attributed to NOS and BAS ship emissions of NO x and particles also after the introduction of stricter SECA regulations in 2015. In addition, several regional studies focusing on the effects of NOS and BAS ship emissions have been performed. Jonson et al. (2015) studied the effects of reducing the sulphur content in marine fuels from 1.5 to 1% in 2011 on air pollution, including also calculations of health effects as well as effects of future (2030) ship emissions. They found that the introduction of a NECA from 2016 (later postponed to 2021) would reduce the burden on health due to shipping in the BAS region. 20 Reductions in future PM 2.5 (particulate matter with diameter less than 2.5µm) levels as a result of the 2021 NECA are also predicted by Karl et al. (2018). Brandt et al. (2013) calculated the effects of ship emission on Europe for the years 2000 and 2020. They found that the implementation of the stricter SECA regulations in the BAS and the NOS would result in substantial health improvements in Europe. Karl et al. (2019) compared the effects of BAS shipping calculated by three different chemistry transport models using year 2012 emissions and meteorology. They found that in the entire BAS region the average contribution 25 from ships to PM 2.5 is in the range of 4.3 -6.5% for the three CTMs, and deposition of oxidised nitrogen to the Baltic Sea in the 20 -24ktN per year range. Claremar et al. (2017) calculated the dispersion of air pollutants and depositions from NOS and BAS shipping for the period 2011 to 2050 with the main focus on sea-water acidity in BAS. They found that, also in the future, ship emissions could remain a major source of acidity, in particular when assuming high penetration of open loop scrubbers in combination with the use of high sulphur-content fuels. 30 In this paper we have calculated the effects of ship emissions in the BAS on air pollution and depositions of oxidised sulphur and nitrogen in adjacent countries. Calculations have been made applying BAS emissions prior to (2014) and after (2016) the implementation of the stricter SECA regulations, which went into force on 1 January 2015. Furthermore, model calculations have been made with future (2030) land-based and ship emissions. The health impacts of air pollutants and the increased depositions of acidifying and eutrophying species from BAS shipping based on these results will be discussed in two companion papers that are in preparation (Barregård et al., 2019;Repka et al., 2019).

Emissions
Land-based emissions have been provided by the International Institute for Applied Systems Analysis (IIASA) within the 5 European FP7 project ECLIPSE. In this study we use version 5a (hereafter 'ECLIPSEv5a'), a global emission data set on 0.5 x 0.5 degree resolution, which has been widely used in recent years by the scientific community (http://www.iiasa.ac.at/web/ home/research/researchPrograms/air/ECLIPSEv5.html, Last accessed: 27 February 2019). ECLIPSEv5a is available in 5-year intervals from 2005 onwards, and in this study we have chosen data for 2015 and 2030. In regard to ship emissions in the BAS, we use emission data provided by FMI for the year 2014 (i.e. with 1% maximum sulphur content in fuels in the SECA) and 10 2016 (maximum sulphur content reduced to 0.1% in the SECA). For the remaining sea areas, ship emissions for year 2015 are used from a previous global data set (Johansson et al., 2017).
The emissions from shipping have been calculated with the Ship Traffic Emission Assessment Model (STEAM) based on ship movements from the automatic identification system (AIS) which provides real time information on ship positions. The model requires as input detailed technical specifications of all onboard fuel-consuming systems and other relevant technical 15 details for all ships considered. The data from IHS Global (2017) constituted the most significant source for this information.
The STEAM model is described in Jalkanen et al. (2009Jalkanen et al. ( , 2012Jalkanen et al. ( , 2016 and Johansson et al. (2013Johansson et al. ( , 2017. Daily emission grids for Baltic Sea ship emissions were produced based on vessel-specific modelling, considering the changes in fuel sulphur content that occurred between 2014 and 2016. Differences between 2014 and 2016 emission data also include changes in ship activity and routing, but on a regional scale these effects are assumed to be small, so that the modelled difference in air pollution 20 and deposition mainly reflects the change in sulphur content in ship fuel.
From 2021 onward, NO x emissions for new ships have to comply with IMO Tier 3 regulations. These contributions were taken into account in the emission modelling. Future emission projections for the year 2030 also include changes in: energy efficiency improvements, modelled following the method of Kalli et al. (2013), which goes beyond the Energy Efficiency Defined Index (EEDI) requirements of the IMO; 25 vessel size growth, assuming a linear annual growth dependent on ship types; fleet size increase.
Annual growth rates in fleet size are implemented as percentage increase per type of ship: For example, if the annual percentage growth is n% for container ships we duplicate n% of the container ships in the current fleet in the following year.
As the ship emission data are used for multiple meteorological years (see next section), we did not retain the high (hourly) 30 temporal resolution in the data but rather aggregated them to monthly resolution before use in the chemistry transport model.

Model calculations of air pollutants and depositions
Concentrations of air pollutants and depositions of sulphur and nitrogen have been calculated with the EMEP MSC-W model (hereafter 'EMEP model'), version rv4.14, on 0.1 x 0.1 degrees resolution for the domain between 30 degrees W and 45 degrees E and between 30 and 75 degrees N. The calculations of dry depositions are made separately for each sub-grid landcover classification. These sub-grid estimates are aggregated to provide output deposition estimates for broader ecosystem categories 5 as deciduous and coniferous forests. The ecosystem specific depositions are not shown here, but will be used in a companion paper when calculating exceedances of critical loads for acidification and eutrophication.
A detailed description of the EMEP model can be found in Simpson et al. (2012) with later model updates being described in Simpson et al. (2018) and references therein. The EMEP model is available as Open Source (see https://github.com/metno/ emep-ctm, Last accessed: 27 February 2019), and is regularly evaluated against measurements as part of the EMEP status 10 reports. See Gauss et al. (2016    In the future scenarios it is assumed that ships that are in compliance with the NECA regulations will operate the equipment (i.e. be compliant) also when sailing outside the NECA.

Model results
In this section model results for parts of Europe centred around the BAS are shown. Concentrations and depositions are shown as averages for three meteorological years for Present_Base and Future_Base and for differences between the two Base runs and 30 the perturbation scenarios as described in Section 1.2. The impact on PM 2.5 levels and on the depositions of oxidised nitrogen and sulphur species derived from the perturbation model runs presented here, forms the basis for coming papers discussing the effects on human health (Barregård et al., 2019) and assessing the environmental impacts, including the exceedances of critical loads from ship emissions in the BAS .  Figure 1c shows the difference between the Present_Base and the Present_NoShip scenarios The calculations show that ship emissions account for more than 50% of NO 2 in central parts of the BAS and for a substantial 10 percentage also in coastal zones, in particular in Denmark, southern parts of Sweden and Finland and the Baltic states (Estonia, Latvia and Lithuania). This is also illustrated in Table 1 where measured NO 2 at sites located in the BAS coastal regions are compared to the Present_Base, Present_NoShip and Present_HiSulphur model calculations. The corresponding time series plots for NO 2 are shown in Appendix A. In the Present_NoShip case NO 2 levels are clearly underestimated and correlations and RMS errors deteriorated compared to the Present_Base calculation, demonstrating the impact of ship emissions in many 15 coastal areas. The comparisons with measurements convincingly show that the measurements can only be reproduced when BAS ship emissions are included. The contributions to individual countries will be further discussed in a later section.

Air pollution due to Baltic Sea shipping
As shown in Table 1 (Present_HiSulphur) has much larger effects, resulting in an overestimation of SO 2 levels at most of the sites listed in Table 1.
This clearly illustrates the effects of the stricter SECA regulations -with the high ship emissions of 2014, the measurements for 2016 can not be reproduced. This is also a strong indication that the ships are largely in compliance with the SECA regulations.
As for NO 2 , the contributions to individual countries are discussed further in a later section PM 2.5 in the atmosphere is a mixture of many chemical species of both natural and anthropogenic origins. It is emitted 25 both as a primary pollutant and formed as a secondary pollutant in the atmosphere. As a result PM 2.5 concentrations are more spread out compared to NO 2 . Concentrations decrease from south to north from a maximum in central Europe. As shown in  Table 1. For PM 2.5 differences between the Present_Base and the Present_NoShip cases are much smaller than for NO 2 . Likewise, differences are smaller than for SO 2 between Present_Base and Present_HiSulphur. The model results underestimate the measurements at most of the sites listed. Based only on the comparisons between measurements and the different model scenarios for PM 2.5 one can not conclude that the Present_Base scenario is more realistic than the other two. As for NO 2 and SO 2 , the contributions to individual countries are discussed further in a later section.

Depositions of sulphur and nitrogen from Baltic Sea shipping
Total depositions (wet and dry) of oxidised sulphur and nitrogen for Present_Base are shown in Figure 2a Dry deposition is parameterised as a function of sub grid-scale ecosystems and is typically higher than the grid average for 10 forest ecosystems (both coniferous and deciduous). This will affect the calculations of critical loads for acidification and eutrophication as the sub grid-scale ecosystem depositions are used in the critical load calculations. Critical loads will be discussed in a companion paper .  up contributions from different sources, have shown that this assumption is reasonable (Jonson et al., 2017(Jonson et al., , 2018. Irrespective of species and depositions, the largest contributions are seen for smaller countries with long coastlines exposed to the BAS as Denmark and the Baltic States, and the least for large countries as Germany and Poland with major parts of their areas located far from the shipping routes.  Our calculations clearly show that, following the stricter SECA regulations from 1 January 2015, sulphur emissions from BAS shipping now contribute little to depositions of oxidised sulphur and PM 2.5 concentrations in air. This is in contrast to pre-2015 conditions when less stringent sulphur regulations were in place, and even more compared to pre-2011 conditions when up to 1.5% sulphur were allowed in marine fuels in the SECAs. BAS ship emissions also affect the formation of ground level ozone. In much of the BAS region NO 2 levels are already influenced by large land-based sources, and additional contributions from BAS shipping to ozone and ozone metrics, exemplified by SOMO35, is moderate, and for several regions even negative. In this paper we have shown that for most countries future 20 ozone and ozone metrics are expected to decrease from their present levels. In addition to influencing particle formation and ozone levels, NO x emissions also contribute to the depositions of oxidised nitrogen, causing exceedances of critical loads for acidification and in particular eutrophication. A significant portion of the depositions of oxidised nitrogen is due to BAS shipping. This is also corroborated by the source-receptor calculations for the individual countries in Europe for 2016, see Klein et al. (2018) where they calculate that BAS shipping is the largest contributor 25 to oxidised nitrogen deposition in Estonia (with 14%), and among the 3 to 5 largest contributors in several other countries in the region. As discussed above, these depositions are projected to be gradually reduced following the implementation of the NECA regulations, with relative reductions largely comparable to the decrease from other anthropogenic sources.