As a consequence of the global distribution of manufacturing sites and the increasing international division of labor, ship traffic is becoming more and more important as an origin of air pollution. Particularly contamination due to the emissions from large cruise and cargo ships is responsible for pollution of the sea as well as the urban harbor environment.

The effects of ship traffic on air pollution and nutrient deposition was studied in an area with one of the highest ship traffic densities in the world, the North Sea region including the English channel. The ship emissions are based on a detailed ship traffic statistics of Lloyd's Marine Intelligence Unit (LMIU) for the North and Baltic Seas for the year 2000. It consists of a vessel characteristic database and a vessel movement database and it includes all commercial vessels equal to or greater than 100 gross tonnages (GT). Emission factors were taken from literature (Cooper and Gustafsson, 2004, ) .

The contribution of ship emissions to the modeled concentration and deposition distribution of sulfur dioxide, nitrogen oxides and of sulfur and nitrogen containing aerosol compounds in North Sea coastal areas were investigated. For this purpose the Community Multiscale Air Quality modeling system (CMAQ, (Byun and Ching, 1999)) was applied on a 54 x 54 km² grid for Europe and on an 18 x 18 km² nested grid for the North Sea area. Meteorological data for the year 2000 was taken from model runs with MM5 (Grell et al., 1995) driven by ERA40 6 hourly reanalysis data. We used four dimensional data assimilation of the ERA40 fields in MM5 and applied the following physical parameterization schemes: Reisner 2 (Reisner et al., 1998) for cloud microphysics, Kain Fritsch 2 (Kain, 2004) for cumulus representation and the MRF scheme (Hong and Pan,1996) for the boundary layer. This setup was tested to produce meteorological data that is as close as possible to wind, temperature and humidity observations (Matthias et al., 2009).

The results show that northern Germany, Denmark and southern Sweden are highly affected by increased concentrations of nitrate and sulfate aerosols that originate from emissions of NO_x and SO₂ from ships travelling in the North Sea. The deposition of nitrogen compounds into the North Sea and other coastal waters is significantly enhanced by ship emissions. This refers not only to the emitted nitrous oxides, but also to the formation of ammonium sulfate aerosols caused by the high SO₂ emissions from ships. This leads to an increased ammonium deposition to the North Sea.

Several emission reduction scenarios which are discussed for the North Sea region or are already implemented were applied and their effects on air pollution and nutrient deposition were studied. This includes • the reduction of SO₂ emissions from ships within a sulfur emission control area (SECA), as it is in place in the North Sea region since 2007 (sulfur limit in fuels < 1.5% S). • the reduction of SO₂ emissions from ships within the SECA since mid 2010 (sulfur limit in fuels < 1.0% S). • the reduction of SO₂ emissions from ships within the SECA planned for 2015 (sulfur limit in fuels < 0.1% S). • the reduction of NO_x emissions as proposed by IMO (MARPOL Annex VI (IMO, 2008) for nitrogen emission control areas starting in 2016 and looking at the effects in 2020 and 2030

The reduction of the sulfur content in fuels significantly reduces the amount of sulfur compounds in the atmosphere. On the other hand, caused by the complex interactions between sulfur and nitrogen aerosol compounds, nitrate aerosol formation and therefore deposition of oxidized nitrogen is enhanced when SO₂ emissions are reduced. NO_x emission reductions as proposed in MARPOL Annex VI have very limited effects on air pollution during the first years of the implementation because only new ships are affected by the regulations. The effect increases with time but it is partly compensated by a further increase in ship traffic.

The development of an updated emission inventory for 2010 is under way. It is based on AIS ship movement data stored in hourly resolution. Ships will be categorized in 10 different types and 8 different size classes for each type. First emission maps and atmospheric pollutants concentrations fields for the North Sea area will be shown, too.