For the years after 2007, the MACC emissions were scaled using the emission trends of each country from EMEP. For those emission groups missing from the MACC

inventory (natural, marine, volcanic and Iceland emissions) the EMEP emissions were used. For north-western Russia (the Kola Peninsula, Karelia and Leningrad Oblast) the FMI’s own inventory is still used, because the locations of the enterprises there are more exact; also there are some well-known sources, e.g. in Karelia, missing from the MACC inventory. For the Baltic Sea model we use the specific Baltic Sea ship emission inventory. This AIS-signal-based inventory was developed at the FMI in co-operation with researchers from Åbo Akademi University and Turku University and with the support of the Marine Administration, FMA, and the Finnish State Technical Research Centre, VTT (Stipa Selleck Epacadostat et al. 2007). Each ship over the 300 tons gross tonnage limit sailing the BS has to send AIS-transmitter safety signals at variable time intervals: these signals contain the unique IMO code of the ship and information on the ship’s movements, its load, destination and type. These signals are collected by AIS-receiver stations located on the coasts of the Baltic Sea. The FMA collects the AIS signals into a local database and sends this information, as do also the other maritime administration offices surrounding the BS, to the HELCOM database (DB).

FMI, having access to the HELCOM DB, decodes the AIS-signals Y 27632 and, using the IMO code, retrieves information on the ship’s machinery from the Lloyds data base. The FMI model STEAM (Ship Traffic Farnesyltransferase Emission Assessment Model, Jalkanen et al. 2009) calculates an emission estimate for each individual ship as a function of the ship’s type, its engine load, fuel type, speed and emission control technology, using current weather and wave height information, and sums the emissions on a latitude-longitude grid with a selected resolution, then reporting on-line using a ∼ 450 s–1 h time-interval.

Emissions calculated with STEAM are available from 2006 onwards. That year the temporal coverage of the signals collected was about 93%, while around 16% of ships sailed without an IMO number (Jalkanen et al. 2012). For small pleasure boats and other vessels, we use the VTT emission inventory. When the AIS signal data are missing, the monthly average emission estimate has been used. The FMI, MACC and EMEP estimates of the BS international ship traffic emissions are compared in Table 1. Over the BS, North Sea and the English Channel the maximum allowable sulphur content of marine fuels decreased due to the EU directive (2005/33/EC) from 1.5 to 1% in July 2010, and to 0.1% in port areas in January 2010. From the year 2009 to 2011, the FMI-estimated ship emissions of SO2 decreased by 48 kt and the EMEP emissions by 40 kt SO2.