Intercomparison of ship emission data models for the North and Baltic Sea region

International ship traffic is steadily increasing since many years. The associated emission of pollutants like sulphur and nitrogen compounds has strong effects on the coastal air quality and the environment. For instance, investigations of Sofiev et al. (2018) show that the ships contribute about 20 % to the sulphur dioxide and 9 % to the global emission of nitrogen oxides. Thus, shipping is also important for climate change  through emissions of greenhouse gases and aerosol particles and the input of acidifying and eutrophying substances into coastal waters.

Therefore, an accurate estimation of ship emissions and their spatio temporal distribution is an important key to understand and investigate coastal ecosystems. The major prerequisite is a precise record of ship movements and related pollutant emissions. In our contribution we present an intercomparison between different ship emission data models for the North and Baltic Sea region. That is the inventory of the Bundesamt für Schiffahrt und Hydrography (EMMA) and the inventory of the HZG (HiMEMO-Ship, Aulinger 2016) are compared against a reference inventory from the Finnish Meteorological institute (STEAM, Jalkanen 2012). The HiMEMO-Ship is a highly flexible tool under ongoing development and allows for temporally and spatially highly-resolved ship emission data (>=30min and >=500 m) of 9 chemical species including aerosols. The tool is designed to consider also adaptation scenarios (e.g. MARPOL Annex VI regulation).
The uncertainty of the derived emissions are discussed on the basis of two means: a) a multi-parameter ensemble generated with the HZG-model and b) a multi-model ensemble using the 3 afore-mentioned approaches (“EMMA”, ”STEAM” and “HiMEMO-Ship”). The results imply that a large portion of emissions are related to ships with actually only insufficiently known characteristics, which thus cause a large range of uncertainty regarding their emission factors. Moreover, a large spread for mean NOx emissions is detected between inventories for the North Sea region. Because of complex manoeuvers and machine handling in the busy port areas, we also observe significant differences in emissions in that regions. Finally, a strategy is presented for treating the afore-mentioned issues with ship emission data in the framework of atmospheric chemistry transport modelling, i.e. deposition of pollutants
from the air.