Ship Emissions and the use of current air cleaning technology : contributions to air pollution and acidification in the Baltic Sea

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 knowledgeof dispersion and deposition of air pollutants is required. Regional model calculations of the dispersion andconcentration of sulfur, nitrogen, and particulate matter, as well as deposition of oxidized sulfur and nitrogenfrom the international maritime sector in the Baltic Sea and the North Sea, have been made for the years 2011to 2013. The contribution from shipping is highest along shipping lanes and near large ports for concentrationand dry deposition. Sulfur is the most important pollutant coupled to shipping. The contribution of both SO2concentration and dry deposition of sulfur represented up to 80% of the total in some regions. WHO guidelinesfor annual concentrations were not trespassed for any analysed pollutant, other than PM2:5 in the Netherlands,Belgium, and central Poland. However, due to the resolution of the numerical model, 50 km50 km, there maybe higher concentrations locally close to intense shipping lanes.Wet deposition is more spread and less sensitiveto model resolution. The contribution of wet deposition of sulfur and nitrogen from shipping was up to 30%of the total wet deposition. Comparison of simulated to measured concentration at two coastal stations close toshipping lanes showed some underestimations and missed maximums, probably due to resolution of the modeland underestimated ship emissions.A change in regulation for maximum sulfur content in maritime fuel, in 2015 from 1 to 0.1 %, decreasesthe atmospheric sulfur concentration and deposition significantly. However, due to costs related to refining, thecleaning of exhausts through scrubbers has become a possible economic solution. Open-loop scrubbers meet theair quality criteria but their consequences for the marine environment are largely unknown. The resulting potentialof future acidification in the Baltic Sea, both from atmospheric deposition and from scrubber water alongthe shipping lanes, based on different assumptions about sulfur content in fuel, scrubber usage, and increasedshipping density has been assessed. The increase in deposition for different shipping and scrubber scenariosdiffers for the basins in the Baltic Sea, with highest potential of acidification in the southern basins with hightraffic. The proportion of ocean-acidifying sulfur from ships incr