In 1997 the International Maritime Organisation (IMO) adopted MARPOL Annex
VI to prevent air pollution by shipping emissions. It regulates, among other
issues, the sulfur content in shipping fuels, which is transformed into the
air pollutant sulfur dioxide (SO
Shipping is a major part of the global transportation sector and its importance is still growing. According to the United Nations Conference on Trade and Development's Review of Maritime Transport, in 2013 a total of 9.6 billion tons were transported via ships. This corresponds to a growth rate of this sector of 3.8 % per year (UNCTAD, 2014). Despite being the most efficient and least emitting mode of transportation per ton of cargo compared to land-based or airborne transport, shipping emissions nevertheless are a considerable fraction of total anthropogenic emissions and have a significant impact on the air quality of coastal areas. 70 % of shipping emissions are produced within 400 km off the coasts (Corbett et al., 1999) and can cause severe health and environmental problems to these regions (Corbett et al., 2007; Eyring et al., 2010).
The International Maritime Organisation (IMO), an agency of the UN with 171
member states, has decided on measures to limit the impact of shipping
emissions by adopting MARPOL Annex VI in 1997. One part of
these measures, and on which this study focuses, is the reduction of
sulfur in ship fuel in order to reduce sulfur dioxide (SO
The IMO regulations concerning sulfur content came into force in 2005 and were revised in 2008; the revision came into force in 2010. For all oceans worldwide, the sulfur content allowed in HFOs was capped at 4.5 %, and after 2012 this limit was reduced to 3.5 %. In addition, so-called “Sulfur Emission Control Areas” (SECA) were established with an even further reduced sulfur limit. One SECA is along the North American coast, and another one comprises the Baltic Sea and the North Sea up to the Shetland Islands and to the western entrance of the English Channel. Within these SECAs the sulfur limit was initially set to 1.5 %, which was reduced to 1.0 % in 2010 and has now reached its current reduction step in January 2015 with a limit of 0.1 %.
While the 1 % limit could still be met with sulfur-reduced HFO, the new regulation forces ships to either use more expensive alternatives such as marine gas oil (MGO), or ultra-low sulfur HFO, or consider reconstruction to enable the use of alternative fuel such as liquefied natural gas (LNG) or methanol. As an alternative technology, the operation of exhaust gas cleaning systems (scrubbers) is also permitted, as long as it provides the same level of protection against sulfur dioxide emissions as the use of low sulfur fuel. These alternative options have been deployed to some ships and first studies have documented their effectiveness and economic efficiency (Reynolds, 2011; Jiang et al., 2014), but they are still under development and not very widespread, and for the vast majority of ships, the only option to meet the regulations is to use desulfurised fuel.
With the regulations in place, the question remains on how to efficiently verify compliance of the ships. To date, compliance is checked by inspection authorities who enter ships at berth, review fuel log books and fuel quality certificates and, if suspicion is raised, take a fuel sample to be analysed at certified laboratories. With the results of these analyses, it is possible to verify compliance and if needed, take legal action. However, these controls can check just a minor number of ships. It is also not possible to evaluate the performance and compliance of scrubber technology by sulfur prediction in bunker oil samples which would be problematic if this method becomes more popular and common in future. Another problem is to control ship fuel of ships on the open sea.
For these reasons, several studies have suggested the implementation of air quality measurement systems especially aiming at the surveillance of ship emissions. One simple but efficient method is direct and simultaneous measurements of pollution trace gases with in situ instruments. These instruments can quite easily be adapted to measurement conditions on aeroplanes, research vessels and trucks and have been used in a variety of campaigns in recent years (Sinha et al., 2003; Schlager et al., 2006; Agrawal et al., 2009; Williams et al., 2009; Diesch et al., 2013; Balzani Lööv et al., 2014; Beecken et al., 2015). Based on the experience from those studies, we have established a measurement station near the harbour of Hamburg to monitor ship emissions, in order to estimate sulfur contents of fuel on board of passing individual ships. Our ship emissions data set from September 2014 to January 2015 documents the quality of implementation of the MARPOL VI regulation with respect to compliant sulfur content in shipping fuel used in SECAs and follows the recent strong tightening of the regulation on 1 January 2015.
The measurements reported here were conducted as part of the Mesmart project, a cooperation between the University of Bremen and the German Federal Maritime and Hydrographic Agency.
Hamburg harbour is the third largest harbour in Europe and the 14th largest worldwide. In 2014, it had a 20-foot standard container throughput of 9.7 billion containers according to Hamburg port statistics. On average there are 800 calls per month, of which more than half are container vessels, and the other half consists mainly of reefer vessels, tankers and bulk carriers. The harbour is located at the mouth of the river Elbe about 110 km inland; see Fig. 1.
Location of the measurement station on the northern bank of the river Elbe, near Hamburg harbour. On the right: picture of instrument box. Map source: OpenStreetMap.
Measurements were conducted next to the river Elbe in the town of Wedel,
which is near Hamburg, on the property and with the support of the Waterways
and Shipping Office Hamburg. The instruments were set up right at the
northern banks of the Elbe, with an approximate line of sight distance to
ships leaving and entering Hamburg harbour of 0.3 and 0.5 km respectively.
The average main wind direction at this location has a southerly
component, so for most of the time within the measurement period, the
exhaust plumes of the ships were blown to the instruments. The area in the
main wind direction south of the measurement station and the Elbe is rural
and sparsely populated with no significant sources of air pollution. Thus
the location of the monitoring site is optimal for relatively low background
concentrations of nitrogen oxides (NO
The concentrations of SO
NO
For SO
For NO
For CO
The trace gas measurements were complemented with measurements of wind, temperature, air pressure and precipitation by a compact weather station (Lufft WS600). With an AIS (automatic identification system) receiver the information transmitted by passing ships was collected, which includes identification number, name and type of the ship as well as position, course and speed.
To obtain the sulfur content of ship fuel in use, the enhancement of
SO
When wind conditions are favourable for measurements, the plumes of ships
passing the instrument leave a distinctive enhancement of the measured
component against background concentrations. Since this enhancement is most
significant in NO measurements, and NO is an indicator for recent combustion
processes, these NO peaks are used to identify the time stamp of a ship
emission event. For these time stamps, peaks in CO
The second part of the data analysis is the attribution of the identified emission events to individual passing ships. Within 30 min before each event, which is characterised by the time the emissions arrive at the instruments, the AIS data are analysed for ship positions close to the measurement site. In combination with wind information, this yields the identification of the individual ships which have caused the emission in most cases. The time the plume travels from being emitted to being analysed is about 2 to 10 min, depending on wind speed and direction. However, there are events in which there are two or more ships too close to each other, or where no AIS signal was received, such that no single ship can be associated to the signal. These events are excluded from the data set.
There are several aspects that influence the accuracy of the calculated
values of the sulfur content for each ship. The SFC formula Eq. (1) assumes a
100 % conversion from sulfur to SO
The uncertainty or sum of systematic and random error of our measurements is
determined from a combination of the calibration uncertainty and the
uncertainty resulting from the signal to noise ratio (SNR). CO
Comparison of absolute NO and SO
All uncertainties added up with the root of sum of squares method; this gives us an uncertainty range for the sulfur content calculations of 15–30 %.
Using the method described above we were able to identify 824 ship plumes of 474 individual ships within the months of September, November and December 2014. Unfortunately no data are available in October due to instrumentation problems. This data set is the so-called pre-regulation-change set, where the regulatory sulfur fuel content allowed for the ships of is 1.0 %. The January 2015 data set consists of 589 ship plumes of 374 individual ships, which since 1 January 2015 have to comply with the new 0.1 % rule. As shown in Fig. 3, the difference between these two data sets is remarkably obvious.
In the pre-regulation-change data set, 99.6 % of all ships complied with the 1 % sulfur limit with respect to the measurement uncertainty. This is better than previously published compliance rates of 85 % of 174 ship plumes (Beecken et al., 2014), although it should be noted that this study did not describe the uncertainty considerations and was measured by aeroplane on the open sea. The latter may imply that compliance might not be so high when no direct control is possible. Compliance rates at other locations for land-based measurements show values of 90 % of 255 ship plumes and 97 % of 211 ship plumes (Beecken et al., 2015). However, a study of Diesch et al., 2013, that describes measurements with a mobile laboratory along the Elbe River near our measurement site, found a compliance of nearly 100 % for 139 ship plumes. This could possibly be credited to the special location of Hamburg harbour where ships have to go up the Elbe for more than 100 km.
In accordance with the practice in use that fuel samples analysed in laboratories are considered as exceeding the 0.1 % sulfur limit in a legally binding way above the value of 0.149 %, we suggest using a corresponding value of 0.15 % as a limit value for discussing the compliance of the ships in our January 2015 data set. This is in consistence with the formerly stated measurement uncertainties. In Fig. 4, a more detailed graph of the January 2015 data is shown. The red line shows the 0.1 % limit with the shaded area, indicating a conservative 30 % measurement uncertainty. The blue line indicates the suggested 0.15 % limit for compliance discussion. Of all the ships measured in January, 95.4 % were complying with the new regulation. There are preliminary results for first SFC measurements in January 2015 presented in Beecken, 2015, which are comparable with our measurements, although with slightly higher uncertainty and lower compliance rates.
The lengths of the ships in 50 m size steps are colour-coded in Figs. 3 and 4. Even before the regulation change, ships smaller than 100 m did not use fuel with sulfur values higher than 0.2 %, most likely because their engines cannot process such fuels or because storage capacity for two different kinds of fuels is not available. After the regulation change, those smaller ships still do not use fuels that reach up to the 0.1 % limit allowed. If one considers only those ships longer than 100 m that could choose which fuel to use and had to change their way of operation, the compliance drops to 93 %.
Sulfur fuel content in autumn 2014, and in January 2015, after the change of fuel regulations. The lengths of the ships that have been analysed are colour-coded. While in 2014 only small ships had fuel sulfur contents below 0.2%, nearly all ships fell into this category in January 2015.
The number of ships that can be detected for compliance depends strongly on the wind conditions. Assuming the average number of calls in Hamburg harbour according to Hamburg port statistics of 800 ships per month means that 1600 emission events happen at our measurement station of ships on their way in and out of the harbour. For months with good wind conditions like December 2014 and January 2015, we can detect about 30–40 % of those events, for months with unfavourable wind conditions, like November 2014, this value drops to less than 10 %.
In this study, we have used the method of in situ measurements of trace gases to implement a system to monitor compliance of ships with sulfur fuel content regulations. This has been discussed and suggested before (Balzani Lööv et al., 2014). Here we present a suitable location for permanent stationary measurements near Hamburg harbour, one of the largest harbours in Europe, and demonstrate a measurement approach that successfully characterises emissions from passing ships. We describe the method used to identify ship emission events and the corresponding ships and present a large data set on fuel usage of ships of 1413 analysed ship plumes altogether. This includes one of the first data sets after the most recent regulation change in the North Sea SECA, where fuel sulfur content limits were reduced from 1 to 0.1 % on 1 January 2015.
Detailed view of the January 2015 data set. The lengths of the ships are colour-coded; the red line indicates the 0.1 % limit, with the shaded area representing the upper limit uncertainty of 30 %. The blue line indicates the suggested limit of 0.15 % for flagging ships as exceeding the sulfur fuel content limit allowed.
Our data show that the vast majority (95.4 %) of all the ships we have measured are indeed complying with the new regulation of 0.1 % sulfur fuel content. Compliance has dropped slightly compared to the value of more than 99 % observed for the 1 % sulfur limit in autumn 2014. It should be noted that the global oil price and thus MGO costs for the necessary sulfur quality in January 2015 was the lowest since 2009, which could have a positive influence on the acceptance of the new regulation.
With the described method it is possible to easily and reliably identify those ships that do not comply. It is possible to check 10–40 % of all ships entering and leaving the harbour, depending on wind conditions. This should be interesting to government agencies in charge of the control of the SECAs.
The research project which facilitated the reported study was funded in part by the German Federal Maritime and Hydrographic Agency and the University of Bremen. The authors thank the Waterways and Shipping Office Hamburg and the Institute for Hygiene and Environment, Hamburg, for their help and support.The article processing charges for this open-access publication were covered by the University of Bremen. Edited by: R. Harley