Shipping represents the largest global cargo transport mode, serving more than 80% of total freight transport.
While vessels exhibit comparatively low fuel consumption per unit of cargo-distance, they produce high specific emissions of nitrogen oxides (NOx), sulphur oxides (SOx) and particulate matter (PM).
In 1997, the International Maritime Organization (IMO) adopted the MARPOL Annex VI Regulation to address such AQ issues. This regulation required that, from 1 January 2015, the equivalent fuel sulphur content (FSC) in Sulphur Emission Control Areas (SECAs) dropped from 4.5% m/m down to 0.1% m/m. On 1 January 2020 a maximum FSC of 0.5% will globally be enforced outside SECAs. In the EU, additional requirements for ferries and ships at berth go beyond IMO regulations. This creates requirements to monitor the compliance of ships with sulphur regulations separately in port areas and in the open-seas.
Further to SOx, vessels built after 1 January 2016 sailing in the North American ECA and after 1 January 2021 sailing in the North and Baltic Seas ECA, need to comply with Tier III NOx standards. For liquid fuel vessels, this will largely be achieved using Selective Catalytic Reduction (SCR) devices. It will have to be verified that SCR remains functional in relevant ECAs, creating additional monitoring requirements.
Ships also emit primary PM, in the form of Black Carbon (BC), Organic Carbon (OC), ash and metallic aerosol, that largely resides in the ultrafine particle (UFP<100 nm) range11. PM from vessels is currently not regulated but BC control is under discussion within the IMO, due to its potent impacts on climate12. Secondary aerosol, through the photooxidation of SOx, NOx and OC, also has consequences to coastal AQ. Better understanding of ship PM and its speciation is required for introducing effective regulatory measures.