The new version of the STEAM model (St2, STEAM2, Jalkanen et al. 2012) used in this study also calculates emissions of CO, CO2 and particulate matter (elementary and organic carbon, ash, hydrated SO4). The main advantage of the

new AIS-based inventory is its excellent temporal and spatial resolution. The modelled 2008–2011 average oxidised nitrogen (NOx), reduced nitrogen (NHx) and sulphur (S) depositions are presented in Figure 1. The dry deposition share of the total NOx deposition increases Ku-0059436 ic50 from 10–20% over the northern Gulf of Bothnia to 20–30% in the Sea of Bothnia, the Gulf of Finland and the Gulf of Riga, being 30–40% in the central Baltic Proper and in the southern Baltic Sea. The share of reduced nitrogen in the total N deposition was less than 30% north of Åland, increasing gradually southwards to over 50% in the Kattegat and Belt Sea areas.

There was a rather sharp dry deposition gradient over the shorelines for both INCB024360 nitrogen compounds. The 2008–2011 average depositions of NOx and S caused by the international ship traffic in the BS are presented in Figure 2 and the ship deposition shares of the respective total deposition in Figure 3. The annual sums of the total and ship-emission-originated depositions of sulphur and nitrogen to the BS with a map of BS sub-basins – the Gulf of Bothnia (B1), the Gulf of Finland (B2), the northern Baltic Proper (B3), the southern Baltic Proper (B4) and the Kattegat and the Belt Sea (B5) – are presented aminophylline in Figure 4. The ship emission originated deposition of oxidised nitrogen increased between 2008 to 2011 from 12 to 14% of the BS total NOx deposition, while the respective sulphur deposition declined from 28 to 20% of the total due to the sulphur directive restrictions. Sulphur is effectively dry-deposited

into the sea, only 19–25% of the ship emission originated sulphur deposition is wet deposition. The total modelled NOx deposition to the BS was respectively 6% and 15% lower in 2008 and 2011 but 1% and 5% higher in 2009 and 2010 than the most recent EMEP estimates from HELCOM 2013. The modelled deposition of NHx was respectively 18, 22, 5 and 15% lower than the EMEP estimate for the years 2008–2011. One reason for the difference is the high deposition gradient at the coastline: in Hilatar, the deposition was integrated only over grid points with 100% open water (372 954 km2), while the complete 0.068° Hirlam BS mask of 420 325 km2, also covered non-marine water areas in the BS coastal zone. Total depositions have a rather high seasonal variation (Figure 5). During spring and early summer when the MABL is usually stably stratified, accumulated precipitation is low and storms are rare, depositions have their minimum values.