Abstract. Ship emissions constitute a large,
and so far poorly regulated,
source of air pollution. Emissions are mainly clustered along
major ship routes both in open seas and close to densely
populated shorelines. Major air pollutants emitted include sulfur
dioxide, NOx, and primary particles. Sulfur and
NOx are both major contributors to the formation
of secondary fine particles (PM2.5) and to
acidification and eutrophication. In addition, NOx is a
major precursor for ground-level ozone.
In this paper, we quantify the contributions from international shipping
to European air pollution levels and depositions. This study is based on global and regional model calculations. The
model runs are made with meteorology and emission data
representative of the year 2017 after the tightening of the
SECA (sulfur emission control area) regulations in 2015 but
before the global sulfur cap that came into force in 2020.
The ship emissions have been derived using ship positioning data.
We have also
made model runs reducing sulfur emissions by 80 % corresponding
to the 2020 requirements. This study is based on model
sensitivity studies perturbing emissions from different
sea areas: the northern European SECA in the North Sea
and the Baltic Sea, the Mediterranean Sea and the Black Sea, the Atlantic
Ocean close to Europe, shipping in the rest of the world, and
finally all global ship emissions together. Sensitivity studies
have also been made setting lower bounds on the effects of ship plumes
on ozone formation. Both global- and regional-scale calculations show that for
PM2.5 and depositions of oxidised nitrogen and
sulfur, the effects of ship emissions are much larger when emissions occur
close to the shore than at open seas. In many coastal countries,
calculations show that shipping is responsible for 10 % or more of the
controllable PM2.5 concentrations and depositions of oxidised
nitrogen and sulfur. With few exceptions, the results from the global and
regional
calculations are similar.
Our calculations show that substantial reductions
in the contributions from ship emissions to PM2.5 concentrations
and to depositions of sulfur can be expected in European coastal regions
as a result of the implementation of a 0.5 % worldwide limit of the
sulfur
content in marine fuels from 2020. For countries bordering the
North Sea and Baltic Sea SECA, low sulfur emissions have
already resulted in marked reductions in PM2.5 from shipping
before 2020. For ozone, the lifetime in the atmosphere is much
longer than for PM2.5, and the potential for ozone formation
is much larger in otherwise pristine environments. We calculate
considerable
contributions from open sea shipping. As a result, we find that
the largest contributions to ozone in several regions and countries
in Europe are from sea areas well outside European waters.
Validating management simulation models and implications for communicating results to stakeholders
