Remote Measurements of Gas and Particulate Matter Emissions from Individual Ships
Abstract: Shipping significantly contributes to the world's anthropogenic emissions of sulfur, nitrogen species and particulate matter. These species affect the global radiative forcing as well as local acidification, eutrophication and human health. Studies show that 70 % of the global ship emissions occur within 400 km from land and it is estimated that about 60,000 premature deaths per year are related to these emissions. The importance of limiting the emission of air pollutants from shipping has been acknowledged by the international community, and policy makers have agreed on international legislation to do this. The current regulations include restrictions for the fuel sulfur content (FSC) and engine specific nitrogen oxide emissions. So far checks of fuel quality are conducted only occasionally, about 200 samples per year in the whole of Sweden, by taking bunker fuel samples as part of on-board inspections of ships at berth in harbors. There is a need for more emission measurements to monitor the compliance of individual ships with respect to the new legislation and to investigate their emissions regarding other pollutants. In this study, methods are presented which have been developed, as part of the Swedish project Identification of Gross-Polluting Ships (IGPS), to monitor and examine the gas and particulate matter emissions from individual ships remotely using extractive (sniffer) techniques and passive Differential Optical Absorption Spectroscopy (DOAS). Two systems were developed, one fully-automated for the use from ground based stations and a second one for the use on aircraft to analyze ship emissions at open sea. Additionally, a plume capturing method was developed for detailed analysis of the composition of particles in single ship plumes. The mass specific emission factors of SO2, NOx and particulate matter from individual ships were measured from fixed stations, boats, airplanes and helicopters, covering the Baltic and North Sea regions. Since 2010 the pollutants in ship exhaust of more than 600 individual ship plumes from mobile platforms and more than 3,000 individual plumes from a fixed site at the harbor entrance of Gothenburg were analyzed. The results show a bi-modal behavior for the distribution of the SO2 emission factors, with international traffic on the higher end around 18 g(SO2)/kg(fuel) and regional traffic on the lower end around 5 g(SO2)/kg(fuel). For NOx, the emissions are distributed around 60 g(NOx)/kg(fuel). The uncertainties of these emission factors are estimated to be around 20 % and 25 % for SO2 and NOx, respectively. The majority of the emitted particles are smaller than 100 nm and it was estimated that 70 % of the particle mass is due to particles below 300 nm. The presented methods can be used for reliable control of compliance to legislation and to provide a level playing field for shipping operators. Conducted measurements indicate a compliance level to the until recently valid 1 % IMO sulfur limit of about 85 % for ships at open-sea and of more than 90 % for ships in or near to harbors. A clear impact of the recently introduced sulfur limit of 0.1 % to the observed SO2 emissions can be seen.
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