Effects of ship emissions on air quality in the Baltic Sea region simulated with three different chemistry transport models
Authors: Karl Matthias , Jonson Jan Eiof , Uppstu Andreas , Aulinger Armin , Prank Marje , Sofiev Mikhail , Jalkanen Jukka-Pekka , Johansson Lasse , Quante Markus , Matthias Volker 
Published: May 2019

Abstract. The Baltic Sea is a highly frequented shipping area with busy shipping lanes close to
densely populated regions. Exhaust emissions from ship traffic into the atmosphere
do not only enhance air pollution, they also affect the Baltic Sea environment
through acidification and eutrophication of marine waters and surrounding terrestrial
ecosystems. As part of the European BONUS project SHEBA (Sustainable Shipping and
Environment of the Baltic Sea region), the transport, chemical transformation and fate
of atmospheric pollutants in the Baltic Sea region were simulated with three regional
chemistry transport model (CTM) systems, CMAQ, EMEP/MSC-W and SILAM, with grid
resolutions between 4 and 11 km. The main goal was to quantify
the effect that shipping emissions have on the regional air quality in the Baltic Sea
region when the same shipping emission dataset but different CTMs are used in their typical
set-ups. The performance of these models and the shipping contribution to
the results of the individual models were evaluated for sulfur dioxide (SO2),
nitrogen dioxide (NO2), ozone (O3) and particulate matter
(PM2.5). Model results from the three CTMs for total air pollutant concentrations
were compared to observations
from rural and urban background stations of the AirBase monitoring network in the
coastal areas of the Baltic Sea region. Observed PM2.5
in summer was underestimated strongly by CMAQ and to some extent by EMEP/MSC-W.
Observed PM2.5 in winter was underestimated by SILAM.
In autumn all models were in better agreement with observed PM2.5.
The spatial average of the annual mean O3 in the EMEP/MSC-W simulation
was ca. 20 %
higher compared to the other two simulations, which is mainly the
consequence of using a different set of boundary conditions for the European model
domain. There are significant differences in the calculated ship contributions to the
levels of air pollutants among the three models.
EMEP/MSC-W, with the coarsest grid, predicted weaker ozone depletion through NO
emissions in the proximity of the main shipping routes than the other two models.
The average contribution of ships to PM2.5 levels in coastal land areas is
in the range of 3.1 %–5.7 % for the three CTMs.
Differences in ship-related PM2.5 between the models are mainly attributed
to differences in the schemes for inorganic aerosol formation.
Differences in the ship-related elemental carbon (EC) among the CTMs can be
explained by differences in the meteorological conditions, atmospheric transport
processes and the applied wet-scavenging parameterizations.
Overall, results from the
present study show the sensitivity of the ship contribution to combined uncertainties
in boundary conditions, meteorological data and aerosol formation and deposition schemes.
This is an important step towards a more reliable evaluation of policy options regarding emission
regulations for ship traffic and the planned introduction of a nitrogen emission control
area (NECA) in the Baltic Sea and the North Sea in 2021.