Impact of a nitrogen emission control area (NECA) on the future air quality and nitrogen deposition to seawater in the Baltic Sea region

• Main Authors: M. Karl, J. Bieser, B. Geyer, V. Matthias, J.-P. Jalkanen, L. Johansson, E. Fridell
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-02-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/1721/2019/acp-19-1721-2019.pdf

<p>Air pollution due to shipping is a serious concern for coastal regions in Europe. Shipping emissions of nitrogen oxides (<span class="inline-formula">NO_<i>x</i></span>) in air over the Baltic Sea are of similar magnitude (330&thinsp;<span class="inline-formula">kt yr⁻¹</span>) as the combined land-based <span class="inline-formula">NO_<i>x</i></span> 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 <span class="inline-formula">NO_<i>x</i></span> 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 <span class="inline-formula">4×4</span>&thinsp;<span class="inline-formula">km²</span> 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 (<span class="inline-formula">NO₂</span>) concentrations over the Baltic Sea. In the business-as-usual (BAU) scenario, with the introduction of the NECA, <span class="inline-formula">NO_<i>x</i></span> emissions from ship traffic in the Baltic Sea are reduced by about 80&thinsp;% in 2040. An approximate linear relationship was found between ship emissions of <span class="inline-formula">NO_<i>x</i></span> and the simulated levels of annual average <span class="inline-formula">NO₂</span> over the Baltic Sea in the year 2040, when following different future shipping scenarios. The burden of fine particulate matter (PM<span class="inline-formula">_2.5</span>) over the Baltic Sea region is predicted to decrease by 35&thinsp;%–37&thinsp;% between 2012 and 2040. The reduction in PM<span class="inline-formula">_2.5</span> is larger over sea, where it drops by 50&thinsp;%–60&thinsp;% along the main shipping routes, and is smaller over the coastal areas. The introduction of NECA is critical for reducing ship emissions of <span class="inline-formula">NO_<i>x</i></span> to levels that are low enough to sustainably dampen ozone (<span class="inline-formula">O₃</span>) 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 PM<span class="inline-formula">_2.5</span> by 72&thinsp;% in 2040 compared to the present day, while it is reduced by only 48&thinsp;% 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 <span class="inline-formula">NO₂</span>, sulfur dioxide and PM<span class="inline-formula">_2.5</span> and daily maximum <span class="inline-formula">O₃</span> 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&thinsp;%–44&thinsp;% 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.</p>