IDENTIFICATION OF GROSS POLLUTING SHIPS
The aim in this project is to develop and test techniques for the surveillance of gas emissions of SO2 and NOx from ships, to enforce new low sulfur regulation within the International Maritime Organization (IMO). The regulation puts a cap on the sulfur fuel content of 1.5% for ships traveling on the Baltic Sea, North Sea and the English Channel. It is driven by the fact that the emissions of sulfur and NOx in Europe are projected to exceed the land based emissions by 2020. Low sulfur fuel is expensive and since surveillance methods for ship emissions are missing it is questionable whether the new legislation will be respected. This project has been funded by Vinnova, the provincial government of Västra Götaland and the Swedish Maritime Organization.
Two types of instrument systems have been employed: The optical system which measures SO2 and NO2 in the flue gases of the ships remotely, by spectral analysis of direct or reflected solar light. From this it is possible to derive the emission rate in mass per time unit. The other system, denoted the sniffer system, is based on the extraction of flue gases through a sonde into the instruments located either in the airplane or in the stationary measurement location. The concentration ratio of SO2 to CO2 is measured and this value is directly proportional to the sulfur fuel content in the ship plume. The system also measures the NOx to CO2 ratio from which the emission in mass per fuel unit is obtained and emission per kWh as given in legislation. The sniffer measurement requires direct contact with the ship plume. The optical system is unique although a similar technique is applied for global satellite monitoring. Similar systems to the sniffer one have been employed by other research groups for airborne measurements of ship emissions. However, their work has been limited to measurements of a few ships, as part of air pollution campaigns, with no focus on surveillance and legal enforcement.
The sniffer system, when operated in this project, had an estimated measurement uncertainty of 15% for the sulfur content, with a negative bias of 4%, and a 21% uncertainty for the measurements of NOx emission versus axial power (g NOx/kWh). For the optical system the uncertainty is difficult to assess but roughly it corresponds to 30-50%. If one considers the overall uncertainty for SO2, then the sniffer measurement has to measure above 1.8% sulfur fuel content, to detect a non complying ship regarding the IMO limit. For the NOx emissions it is uncertain whether the measurement accuracy of the IGPS system is sufficient to check compliance with the coming regulation requiring 20% reduction (Tier II), but whenever it is decided to introduce environmental control areas for NOx with 80% required NOx reduction (Tier III) then this will be rather easy to control.
In May and June 2007, stationary measurements with the Sniffer and optical system were carried out at Nya Älvsborgs fästning, an old fortress, on the north side of the ship channel into Göteborg. From these measurements, 220 ship plumes corresponding to 80 individual ships, were identified and analyzed. A large fraction of the ship plumes (50 out of 220) corresponded to plumes from ferry boats, predominately from Stena line. The measured data was compared to certain ships for which the sulfur fuel content was known. All in all, a good agreement was obtained when comparing the results to ships with known sulfur fuel values of 0.1%, 0.5% and 1.1%, respectively. This has to be further studied. Three ships out of the eighty were above the IMO limit of 1.5% in the harbor study.
In August 2007 and 2008, respectively, the IGPS (Identification of Gross Polluting Ships) measurement system was installed in the CASA-212 airplane KBV-583 of the Swedish coastguard and 20 test flights with a duration of 2 hours were conducted in the Baltic sea, east of the Island of Gotland, and between Denmark and Sweden. A total of 343 measurements were done with the sniffer instrument corresponding to 95 individual ships. The measurements were shared about equal between SO2 and NOx, being able to measure only these species one at a time in the experimental setup. On average the ships had a sulfur content of 1.28% and only 3 ships were with certainty above the IMO SECA limit of 1.5%, when considering the measurement uncertainty. The ships, on average, emitted 13 gNOx/kWh (66 g NOx/kg fuel) and the ships seemed in general to comply with the Tier I IMO standard, considering the uncertainties. A thorough investigation of emission versus crankshaft speed has not been done, however.
The optical instrument was able to obtain fluxes in 66% of the ship measurements; 70 flux measurements [kg/h] of SO2 or NO2 were conducted on 35 individual ships. On average the SO2 and NO2 emission were 54 kg/h and 33 kg/h, respectively.