The western Baltic Sea is impacted by various anthropogenic activities and stressed by high riverine and atmospheric nutrient loads. Atmospheric deposition accounts for up to a third of the nitrogen input into the Baltic Sea and contributes to eutrophication. Amongst other emission sources, the shipping sector is a relevant contributor to the atmospheric concentrations of nitrogen oxides (NOX) in marine regions. Thus, it also contributes to atmospheric deposition of bioavailable oxidized nitrogen into the Baltic Sea. In this study, the contribution of shipping emissions to the nitrogen budget in the western Baltic Sea is evaluated with the coupled three-dimensional physical biogeochemical model MOM–ERGOM (Modular Ocean Model–Ecological ReGional Ocean Model) in order to assess the relevance of shipping emissions for eutrophication. The atmospheric input of bioavailable nitrogen impacts eutrophication differently depending on the time and place of input. The shipping sector contributes up to 5 % to the total nitrogen concentrations in the water. The impact of shipping-related nitrogen is highest in the offshore regions distant from the coast in early summer, but its contribution is considerably reduced during blooms of cyanobacteria in late summer because the cyanobacteria fix molecular nitrogen. Although absolute shipping-related total nitrogen concentrations are high in some coastal regions, the relative contribution of the shipping sector is low in the vicinity of the coast because of high riverine nutrient loads.

Abstract. The western Baltic Sea is impacted by various anthropogenic activities and stressed by high riverine and atmospheric nutrient loads. Atmospheric deposition accounts for up to a third of the nitrogen input into the Baltic Sea and contributes to eutrophication. Amongst other emission sources, the shipping sector is a relevant contributor to atmospheric concentrations of nitrogen oxides (NOx) in marine regions. Thus, it also contributes to atmospheric deposition of bioavailable oxidized nitrogen into the Baltic Sea. In this study, the contribution of shipping emissions to the nitrogen budget in the western Baltic Sea is evaluated with the coupled three-dimensional physical biogeochemical model MOM-ERGOM in order to assess the relevance of shipping emissions for eutrophication. The input of bioavailable nitrogen impacts eutrophication differently depending on time and place of input – e.g. nitrogen is processed and denitrified faster in flat coastal regions. The shipping sector contributes up to 5 % to the total nitrogen concentrations in the water. The impact of shipping-related nitrogen is highest in the off-shore regions distant to the coast in early summer but is considerably reduced during blooms of cyanobacteria in later summer. Although absolute shipping-related total nitrogen concentrations are high in some coastal regions, the relative contribution of the shipping sector is low in the vicinity to the coast because of high riverine nutrient loads.

Numerical ocean models, like other geoscientific models, are a strongly simplified representation of real oceans. They are used as tools to answer research questions about the real-world systems. Therefore, their thorough validation is essential to ensure that the conclusions drawn from the model experiment are valid in reality. We demonstrate a software which allows an interactive model validation through a web interface based on the R Shiny framework. At pre-defined stations, different kinds of plots can be rendered within a few seconds, according to the user’s choice, allowing a live validation of different model parameters even in model simulations which are still running. This makes it different from validation approaches which generate a pre-defined set of plots after the calculations have finished and make it particularly useful for model tuning purposes. Observation data can be read in from text files or can be extracted from a database.Once set up, the validation tool requires no technical skills to use. It can be used for single- or multi-model validation and allows saving the generated plots as high-resolution images suitable for use in scientific publications.A Linux operating system is required for the Validator app, but via a virtual machine, the software can run on Windows or MacOS hosts as well. A Dockerfile is supplied which allows to test the software with example data without installation. Funding statement: This software was developed at the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) on institutional funding.

My main criticism is that, to calculate a residence time, a model is not needed. Multiplication of observed nutrient inventories with the inverse of the HELCOM nutrient fluxes directly, at the back of an envelope, yields residence times already. According to the authors (c.f. pg. 1, ln. 16-18) these residence times have been already known. I conclude that their model estimate does not present novel concepts, ideas – nor substantial conclusions.

Poor air quality is still a threat for human health in many parts of the world. In order to assess measures for emission reductions and improved air quality, three-dimensional atmospheric chemistry transport modeling systems are used in numerous research institutions and public authorities. These models need accurate emission data in appropriate spatial and temporal resolution as input. This paper reviews the most widely used emission inventories on global and regional scales and looks into the methods used to make the inventory data model ready. Shortcomings of using standard temporal profiles for each emission sector are discussed, and new methods to improve the spatiotemporal distribution of the emissions are presented. These methods are often neither top-down nor bottom-up approaches but can be seen as hybrid methods that use detailed information about the emission process to derive spatially varying temporal emission profiles. These profiles are subsequently used to distribute bulk emissions such as national totals on appropriate grids. The wide area of natural emissions is also summarized, and the calculation methods are described. Almost all types of natural emissions depend on meteorological information, which is why they are highly variable in time and space and frequently calculated within the chemistry transport models themselves. The paper closes with an outlook for new ways to improve model ready emission data, for example, by using external databases about road traffic flow or satellite data to determine actual land use or leaf area. In a world where emission patterns change rapidly, it seems appropriate to use new types of statistical and observational data to create detailed emission data sets and keep emission inventories up-to-date.IMPLICATIONS:Emission data are probably the most important input for chemistry transport model (CTM) systems. They need to be provided in high spatial and temporal resolution and on a grid that is in agreement with the CTM grid. Simple methods to distribute the emissions in time and space need to be replaced by sophisticated emission models in order to improve the CTM results. New methods, e.g., for ammonia emissions, provide grid cell-dependent temporal profiles. In the future, large data fields from traffic observations or satellite observations could be used for more detailed emission data.

A) “Iron reduction and release of phosphate under anoxic conditions in the sediment are not represented in this ERGOM version” (Part A, L 15/8). Fixing sediment N:P ratio and ignoring redox alterations of the P cycle implausibly affects phosphate dynamics, hence, distorts such important flux as nitrogen fixation and the following cycling of fixed nitrogen. The necessity of Si restarting for every year indicates that its dynamics even during the first iteration is erroneous with corresponding consequences for phytoplankton seasonal succession and nutrient uptake. [. . . ]

Abstract. The North Sea and the Baltic Sea are impacted by several anthropogenic activities, which put pressure onto the marine ecosystem. One of these pressures is the input of nitrogen compounds, which act as nutrients for phytoplankton growth and induce eutrophication. Atmospheric deposition is a relevant contributor to the marine nitrogen budget, making up 20 % to 40 % of the nitrogen input of the North Sea and Baltic Sea. But the concentrations of dissolved and particulate nitrogen in the sea are not only determined by the input, but also by the residence time of nitrogen in the system before it is removed by biogeochemical processes or physical advection. Our study aims to estimate the contribution of atmospherically deposited nitrogen to the nitrogen pools of North Sea and Baltic Sea. The contribution of atmospheric nitrogen deposition to dissolved inorganic nitrogen and to particulate organic nitrogen in the surface water was evaluated for both Seas in this study showing the relevance of deposition. Both seas differ significantly with respect to the residence time of water and nutrients. Hence, both water bodies were compared with respect to the accumulation of atmospheric nitrogen. Model simulations with the coupled physical biogeochemical model HBM-ERGOM were performed for this purpose. The fate of atmospheric nitrogen deposition was traced in the marine ecosystem. The model-predicted relevant nutrient concentrations in the surface layer compared well to measurements. Nutrient and oxygen concentrations in deep parts of the Baltic Sea were not properly reproduced but did not impact the simulation quality of surface layer concentrations. The denitrification in the Wadden Sea was underestimated by the model. Tagged dissolved inorganic nitrogen (DIN) with nitrogen from atmospheric deposition reaches a steady-state in the southern North Sea after two years of simulation. This is consistent with the published residence time of nutrients in this region. In contrast, in the Baltic Sea region, the atmospheric nitrogen shares increased year-by-year reaching a steady-state not before the fifth year. This is also consistent with published studies on the residence time of riverine nitrogen in the Baltic Sea. Atmospheric nitrogen shares were evaluated in detail in the second part of this study.

Abstract. Atmospheric deposition accounts for up to a third of the nitrogen input into the Baltic Sea and contributes to eutrophication. It is useful to use three-dimensional biogeochemical models to evaluate the contribution of atmospheric nitrogen deposition to eutrophication because bioavailable nitrogen impacts eutrophication differently depending on time and place of input – e.g. nitrogen is processed and denitrified faster in flat coastal regions. The western Baltic Sea, which is stressed by high nutrient loads, is characterized by many small islands and a wrinkled coast line. In regions with this type of coastal features, the grid resolution of atmospheric chemistry transport models (CTMs) has a strong impact on the modeled nitrogen deposition. The aim of this study was to evaluate the benefit of finer spatially resolved deposition data as input for simulations with the ecosystem model ERGOM. This study also focused on the shipping contribution to the marine nitrogen budget via deposition of shipping-emitted nitrogen oxide (NOx). Differences in the modeled dissolved inorganic nitrogen (DIN) caused by refined nitrogen deposition were identified in some coastal sections and between the Danish islands. Patches of enhanced DIN concentrations were found distant to the coast in model runs forced by the finer resolved data. These were caused by better resolved precipitation events. The differences between fine and coarse resolution deposition of the same CTM were low compared to the difference to EMEP deposition, which was a third comparison data set. The shipping sector contributed a maximum of 10 % and on average less than 5 % to DIN. In summary, particularly small scale ecosystem model studies in bights are expected to benefit from spatially higher resolved nitrogen deposition data. The shipping sector is a relevant contributor to the marine nitrogen deposition but its contribution to the marine DIN pool is rather low.

World seaborne transportation is crucial for world trade and global economic growth. Shipping has been increasing since 2009, including oil & gas, dry bulk and container freight, and is very likely to continue this trend in the near future. However, international shipping also produces 2.7% of the world's total CO2 emissions, and globally, air pollutants emitted from international shipping are increasing due to the rise in trade. It is a well-established fact that Greenhouse Gasses (GHGs) cause climate change and that air pollutants trigger a range of health issues for humans. To demonstrate the applicability of the proposed framework, this paper will focus on a general assessment of the health-related externality of air pollution emitted from wind-assisted hybrid ship propulsion within two different emission reduction scenarios. The paper will further analyse the emission impact from both individual scenarios. A Chemical Transport Model (CTM) is used to estimate the realistic concentration of relevant air pollutants, and the Economic Valuation of Air-pollution Model (EVA) is applied to assessing the health-related economic externalities of air pollution.

Atmospheric sea salt particles affect chemical and physical processes in the atmosphere. These particles provide surface area for condensation and reaction of nitrogen, sulfur, and organic species and are a vehicle for the transport of these species. Additionally, HCl is released from sea salt. Hence, sea salt has a relevant impact on air quality, particularly in coastal regions with high anthropogenic emissions, such as the North Sea region. Therefore, the integration of sea salt emissions in modeling studies in these regions is necessary. However, it was found that sea salt concentrations are not represented with the necessary accuracy in some situations.In this study, three sea salt emission parameterizations depending on different combinations of wind speed, salinity, sea surface temperature, and wave data were implemented and compared: GO03 (Gong, 2003), SP13 (Spada et al., 2013), and OV14 (Ovadnevaite et al., 2014). The aim was to identify the parameterization that most accurately predicts the sea salt mass concentrations at different distances to the source regions. For this purpose, modeled particle sodium concentrations, sodium wet deposition, and aerosol optical depth were evaluated against measurements of these parameters. Each 2-month period in winter and summer 2008 were considered for this purpose. The shortness of these periods limits generalizability of the conclusions on other years.While the GO03 emissions yielded overestimations in the PM10 concentrations at coastal stations and underestimations of those at inland stations, OV14 emissions conversely led to underestimations at coastal stations and overestimations at inland stations. Because of the differently shaped particle size distributions of the GO03 and OV14 emission cases, the deposition velocity of the coarse particles differed between both cases which yielded this distinct behavior at inland and coastal stations. The PM10 concentrations produced by the SP13 emissions generally overestimated the measured concentrations. The sodium wet deposition was generally underestimated by the model simulations but the SP13 cases yielded the least underestimations. Because the model tends to underestimate wet deposition, this result needs to be considered critically. Measurements of the aerosol optical depth (AOD) were underestimated by all model cases in the summer and partly in winter. None of the model cases clearly improved the modeled AODs. Overall, GO03 and OV14 produced the most accurate results, but both parameterizations revealed weaknesses in some situations.

Coarse sea salt particles are emitted ubiquitously from the ocean surface by wave-breaking and bubble-bursting processes. These particles impact the atmospheric chemistry by affecting the condensation of gas-phase species and, thus, indirectly the nucleation of new fine particles, particularly in regions with significant air pollution. In this study, atmospheric particle concentrations are modeled for the North Sea and Baltic Sea regions in northwestern Europe using the Community Multiscale Air Quality (CMAQ) modeling system and are compared to European Monitoring and Evaluation Programme (EMEP) measurement data. The sea salt emission module is extended by a salinity-dependent scaling of the sea salt emissions because the salinity in large parts of the Baltic Sea is very low, which leads to considerably lower sea salt mass emissions compared to other oceanic regions. The resulting improvement in predicted sea salt concentrations is assessed. The contribution of surf zone emissions is considered separately. Additionally, the impacts of sea salt particles on atmospheric nitrate and ammonium concentrations and on nitrogen deposition are evaluated. The comparisons with observational data show that sea salt concentrations are commonly overestimated at coastal stations and partly underestimated farther inland. The introduced salinity scaling improves the predicted Baltic Sea sea salt concentrations considerably. The dates of measured peak concentrations are appropriately reproduced by the model. The impact of surf zone emissions is negligible in both seas. Nevertheless, they might be relevant because surf zone emissions were cut at an upper threshold in this study. Deactivating sea salt leads to minor increases in NH3 + NH4+ and HNO3 + NO3− and a decrease in NO3− concentrations. However, the overall effect on NH3 + NH4+ and HNO3 + NO3− concentrations is smaller than the deviation from the measurements. Nitrogen wet deposition is underestimated by the model at most stations. In coastal regions, the total nitrogen deposition (wet and dry) is considerably affected by sea salt particles. Approximately 3–7 % of atmospheric nitrogen deposition into the North Sea is caused by sea salt particles. The contribution is lower in the Baltic Sea region. The stations in the EMEP network provide a solid basis for model evaluation and validation. However, for a more detailed analysis of the impact of sea salt particles on atmospheric nitrogen species, size-resolved measurements of Na+, NH4+, and NO3− are needed.

The North Sea region is characterised by several anthropogenic activities such as shipping, agriculture, industry and tourism. These activities go along with emissions of air pollutants such as NO X , NH3, and SO2 leading to the formation of HNO3, H2SO4, and particulate matter. Gaseous bases and acids (mainly HNO3, H2SO4 and NH3) tend to form new particles or to condense on existing ones. Meteorological conditions and size distribution of existing particles affect partitioning of these substances between gas and particle phase and between particle modes. In the marine troposphere, sea salt particles (mainly Cl–, Na+ and \({\text{SO}}_{4}^{2 - }\)) account for a considerable amount of fine and coarse particles providing surface for condensation of above mentioned substances. The presence of sea salt may also affect N deposition because dry deposition velocities of gaseous substances and different particle modes vary considerably. In the presented study, the effect of sea salt emissions on atmospheric air pollution in the North Sea region was analysed by the means of the Community Multiscale Air Quality (CMAQ) Model. We simulated on a \(24 \times 24\;\text{km}^{2}\) grid including the North and Baltic Sea. It was found, that the presence of sea salt increases coarse mode \({\text{NH}}_{4}^{ + }\) and \({\text{NO}}_{3}^{ - }\) concentrations considerably while fine mode concentrations are decreased. This leads to increased total N deposition in coastal regions. At the same time, the deposition distant to the shore on the land as well as into the ocean decreases. However, this study shows that on spatial average only about 5 % of N deposition into the North Sea is caused by sea salt particles. Locally, the effect of sea salt on N deposition is partly higher. Therefore, sea salt emissions in regional air quality models are important for predicting the partitioning of anthropogenic pollutants between gas and particle phase and their deposition patterns correctly.

0) Rather than a general evaluation of speciated mass concentrations at certain sites, I think that the model evaluation needs to address scientific questions regarding sea salt emissions such as the chemical composition, size distribution, transport/deposition, and interaction with other aerosol components. While some of these evaluations may not be possible with the limited observational dataset, evaluating groups of stations with similar characteristics (inland vs coastal, remote vs urban, agricultural vs industrial, etc.) as opposed to individual stations may help identify strengths/weaknesses of the existing sea spray emission parameterization besides the lack of salinity-dependence.

The drift of marine litter in the southern North Sea was simulated with the offline Lagrangian transport model PELETS-2D. Assuming different source regions, passive tracer particles were released every 28 h within a nine-year period. Based on pre-calculated hourly wind and ocean current data, drift simulations were carried out forward and backward in time with and without the assumption of extra wind forces influencing particle movement. Due to strong variability of currents, backward simulations did not allow for the identification of particular source regions influencing given monitoring sites. Neither accumulation regions at open sea could be identified by forward simulations. A seasonal signal, however, could be identified in the number of tracer particles that reached the coastal areas. Both particle drift velocity and variability of drift paths further increased when an extra wind drift was assumed.

In the last decades, marine litter has become ubiquitous and has adverse impacts on marine animals through entanglement of mammals, reptiles, sea birds, fish and other animals in discarded and lost fishing gear and other plastic litter items, as well as through ingestion, especially of micro- and mesoplastics, by vertebrates and invertebrates (Figure 1). As part of a project embedded in the implementation of the Marine Strategy Framework Directive (MSFD), we were commissioned to analyze data from monitoring of marine litter, including microplastics, on beaches and in other compartments of the marine environment. Spatial and temporal trends should be identified, and results should be used to classify European marine waters according to their level of pollution with marine litter. Prior to evaluation, indicators of the Good Environmental Status (GES) should be defined, such as the existing OSPAR-EcoQO on the amount of plastic in the stomachs of northern fulmars. Finally for all marine compartments, recommendations for future monitoring of marine litter have to be given.

During the last decades, marine pollution with anthropogenic litter has become a worldwide major environmental concern. Standardized monitoring of litter since 2001 on 78 beaches selected within the framework of the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) has been used to identify temporal trends of marine litter. Based on statistical analyses of this dataset a two-part multi-criteria evaluation system for beach litter pollution of the North-East Atlantic and the North Sea is proposed. Canonical correlation analyses, linear regression analyses, and non-parametric analyses of variance were used to identify different temporal trends. A classification of beaches was derived from cluster analyses and served to define different states of beach quality according to abundances of 17 input variables. The evaluation system is easily applicable and relies on the above-mentioned classification and on significant temporal trends implied by significant rank correlations.

The western Baltic Sea is impacted by various anthropogenic activities and stressed by high riverine and atmospheric nutrient loads. Atmospheric deposition accounts for up to a third of the nitrogen input into the Baltic Sea and contributes to eutrophication. Amongst other emission sources, the shipping sector is a relevant contributor to atmospheric concentrations of nitrogen oxides (NOx) in marine regions. Thus, it also contributes to atmospheric deposition of bioavailable oxidized nitrogen into the Baltic Sea. In this study, the contribution of shipping emissions to the nitrogen budget in the western Baltic Sea is evaluated with the coupled three-dimensional physical biogeochemical model MOM-ERGOM in order to assess the relevance of shipping emissions for eutrophication. The input of bioavailable nitrogen impacts eutrophication differently depending on time and place of input – e.g. nitrogen is processed and denitrified faster in flat coastal regions. The shipping sector contributes up to 5 % to the total nitrogen concentrations in the water. The impact of shipping-related nitrogen is highest in the off-shore regions distant to the coast in early summer but is considerably reduced during blooms of cyanobacteria in later summer. Although absolute shipping-related total nitrogen concentrations are high in some coastal regions, the relative contribution of the shipping sector is low in the vicinity to the coast because of high riverine nutrient loads.