Impact of a nitrogen emission control area (NECA) on the future air quality and nitrogen deposition to seawater in the Baltic Sea region
Authors: Karl Matthias , Bieser Johannes , Geyer Beate , Matthias Volker , Jalkanen Jukka-Pekka , Johansson Lasse , Fridell Erik 
Published: February 2019

Abstract. Air pollution due to shipping is a serious concern for coastal regions in
Europe. Shipping emissions of nitrogen oxides (NOx) in air
over the Baltic Sea are of similar magnitude (330 kt yr−1) as the
combined land-based NOx emissions from Finland and Sweden in
all emission sectors. Deposition of nitrogen compounds originating from
shipping activities contribute to eutrophication of the Baltic Sea and
coastal areas in the Baltic Sea region. For the North Sea and the Baltic Sea
a nitrogen emission control area (NECA) will become effective in 2021; in
accordance with the International Maritime Organization (IMO) target of
reducing NOx emissions from ships. Future scenarios for 2040
were designed to study the effect of enforced and planned regulation of ship
emissions and the fuel efficiency development on air quality and nitrogen
deposition. The Community Multiscale Air Quality (CMAQ) model was used to
simulate the current and future air quality situation. The meteorological
fields, the emissions from ship traffic and the emissions from land-based
sources were considered at a grid resolution of 4×4 km2
for the Baltic Sea region in nested CMAQ simulations. Model simulations for
the present-day (2012) air quality show that shipping emissions are the major
contributor to atmospheric nitrogen dioxide (NO2) concentrations
over the Baltic Sea. In the business-as-usual (BAU) scenario, with the
introduction of the NECA, NOx emissions from ship traffic in
the Baltic Sea are reduced by about 80 % in 2040. An approximate linear
relationship was found between ship emissions of NOx and the
simulated levels of annual average NO2 over the Baltic Sea in the
year 2040, when following different future shipping scenarios. The burden of
fine particulate matter (PM2.5) over the Baltic Sea region is predicted
to decrease by 35 %–37 % between 2012 and 2040. The reduction in
PM2.5 is larger over sea, where it drops by 50 %–60 % along the
main shipping routes, and is smaller over the coastal areas. The introduction
of NECA is critical for reducing ship emissions of NOx to
levels that are low enough to sustainably dampen ozone (O3)
production in the Baltic Sea region. A second important effect of the NECA
over the Baltic Sea region is the reduction in secondary formation of
particulate nitrate. This lowers the ship-related PM2.5 by 72 % in
2040 compared to the present day, while it is reduced by only 48 %
without implementation of the NECA. The effect of a lower fuel efficiency
development on the absolute ship contribution of air pollutants is limited.
Still, the annual mean ship contributions in 2040 to NO2, sulfur
dioxide and PM2.5 and daily maximum O3 are significantly
higher if a slower fuel efficiency development is assumed. Nitrogen
deposition to the seawater of the Baltic Sea decreases on average by
40 %–44 % between 2012 and 2040 in the simulations. The effect of
the NECA on nitrogen deposition is most significant in the western part of
the Baltic Sea. It will be important to closely monitor compliance of
individual ships with the enforced and planned emission regulations.