Monitoring compliance with sulfur content regulations of shipping fuel by in situ measurements of ship emissions

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 (SO2) during combustion. Within designated Sulfur Emission Control Areas (SECA), the sulfur content was limited to 1 %, and on 1 January 2015, this limit was further reduced to 0.1 %. Here we present the set-up and measurement results of a permanent ship emission monitoring site near Hamburg harbour in the North Sea SECA. Trace gas measurements are conducted with in situ instruments and a data set from September 2014 to January 2015 is presented. By combining measurements of carbon dioxide (CO2) and SO2 with ship position data, it is possible to deduce the sulfur fuel content of individual ships passing the measurement station, thus facilitating the monitoring of compliance of ships with the IMO regulations. While compliance is almost 100 % for the 2014 data, it decreases only very little in 2015 to 95.4 % despite the much stricter limit. We analysed more than 1400 ship plumes in total and for months with favourable conditions, up to 40 % of all ships entering and leaving Hamburg harbour could be checked for their sulfur fuel content.


Introduction
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 Re- 20 view of Maritime Transport, in 2013 a total of 9.6 billion t were transported via ships, which 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 im-Introduction  (Corbett et al., 1999) and can cause severe health and environment 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 on the MARPOL Annex VI protocol in 1997. One part of these measures 5 and the one on which this study focuses is the reduction of sulphur in ship fuel in order to reduce sulphur dioxide (SO 2 ) emissions. When oxidised, SO 2 forms small sulphate particles which have an effect on cloud properties and change their reflectivity and lifetime . SO 2 emissions by ships lead to an enhanced sulphate concentration of 10-50 % in coastal areas (Matthias et al., 2010), which increases acid-10 ification by acid rain (Endresen et al., 2003). Gaseous SO 2 as well as sulphate particles have health effects on humans when inhaled. SO 2 is produced during the combustion process by burning sulphur that is contained in the fuel. Ship engines have been developed to be able to burn Heavy Fuel Oils (HFO) that have a very high sulphur content of up to several percent and are basically a waste product of oil refineries and thus very 15 cheap.
The IMO regulations concerning sulphur content came into force in 2005 and were revised in 2008, the revision came into force in 2010. On all oceans worldwide, the allowed sulphur content in HFOs was capped at 4.5 %, and after 2012 this limit was reduced to 3.5 %. In addition, so called "Sulphur Emission Control Areas" (SECA) were 20 established with an even further reduced sulphur 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 sulphur 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 %. 25 While the 1 % limit could still be met with sulphur reduced HFO, the new regulation forces ships to either use more expensive Marine Gas Oil (MGO), 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 Introduction (scrubbers) is also permitted, as long as it provides the same level of protection against sulphur dioxide emissions as the use of low sulphur MGO. 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 5 option to meet the regulations is to use MGO. 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 when suspicion was raised take a fuel sample to be analysed at certified laboratories. With the results 10 of these analyses, it is possible to verify compliance and if needed, take legal actions. 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 sulphur 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 15 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 mea-20 surement conditions on airplanes, 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., 2014b). Based on the experience from those studies, we have established a measurement station near the harbour of Hamburg to monitor ship emissions, 25 to estimate sulphur contents of fuel on board of passing individual ships. Our ship emissions dataset from September 2014 to January 2015 documents the quality of implementation of the MARPOL VI regulation with respect to compliant sulphur content in ACPD 15,[11031][11032][11033][11034][11035][11036][11037][11038][11039][11040][11041][11042][11043][11044][11045][11046][11047]2015 Monitoring compliance with sulphur content regulations of shipping fuel L. Kattner et al. shipping fuel used in SECAs and follows the recent strong tightening of the regulation on 1 January 2015.

Measurement site and methods
The measurements reported here were conducted as part of the Mesmart project, a cooperation between the University of Bremen and the German Federal Maritime 5 and Hydrographic Agency.

Instrumentation
The concentrations of SO 2 , NO x , CO 2 , and Ozone (O 3 ) were measured continuously with individual instruments which are combined in a temperature stabilised box to ensure stable measurement conditions and at the same time provide a compact and transportable set-up. Data are stored in an integrated data logger with the time resolu-5 tion of one minute. Despite different time resolutions of the instruments, we used data normalised to one minute which is sufficient for the analysis of emission events with a duration in the order of several minutes. NO x , SO 2 and O 3 were measured with instruments from the Horiba AP-370 series which are certified instruments used by German authorities for standard air pollution 10 measurements. CO 2 was measured with a Licor 840A analyser. The O 3 measurements were not used for this study and are just mentioned for completeness.
SO 2 : the Horiba APSA-370 is based on the UV-fluorescence method, using the excitation of SO 2 molecules by UV light and measuring the fluorescence which is a function of SO 2 concentration. The response time of the instrument is specified to be less than 15 120 s. Calibration was carried out with a standard gas mixture from Air Liquide with a concentration of 99.7 ppb SO 2 with an accuracy of 5 %. In addition, a daily control was obtained by the measurement of zero gas produced with a scrubber, and span gas from an internal permeation source with 175 ppb SO 2 . CO 2 : the Licor 840A is a non-dispersive infrared gas analyser. It has a response time of 1 s and was calibrated with two Air Liquide standard gas mixtures with 306.6 ppm and 990.0 ppm CO 2 with an accuracy of 2 %.
The trace gas measurements were complemented with measurements of wind, temperature, air pressure and precipitation by a compact weather station (Lufft WS600). 5 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.

Data analysis
To obtain the sulphur content of ship fuel in use, the enhancement of SO 2 and CO 2 in 10 measurements affected by exhaust gases is measured, and the ratio of these SO 2 and CO 2 peaks is used to calculate the fuel sulphur content. The combination of the trace gas peak time, the wind direction, and the AIS information enables the identification of the peak related ship.
When wind conditions are favourable for measurements, the exhaust plumes of ships 15 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 2 are then identified, which is more complicated because back-20 ground concentrations are larger and more variable due to the surrounding vegetation.
Only for those events with a significant CO 2 peak, SO 2 signals are analysed. For all peaks the peak area above the background concentration is determined. This accounts for the difference in peak width for each gas due to different time resolutions of the respective instruments. Introduction

Conclusions References
where A(S) is the atomic weight of sulphur and A(C) of carbon. With this formula it is 5 easy to calculate the sulphur content for each set of peaks. For a discussion about the uncertainties of this formula see Sect. "Uncertainties". 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 is analysed 10 for ship positions close to the measurement site. In combination with wind information it is in most cases possible to identify individual ships having caused the emission. The time the exhaust plume travels from being emitted to being analysed is about 2 to 10 min depending on wind speed and direction. However, there are cases where there are two or more ships too close to each other, or where no AIS signal was received, 15 so that no single ship can be associated to the signal. These events are excluded from the data set.

Uncertainties
There are several aspects that influence the accuracy of the calculated values of the sulphur content for each ship. The SFC-formula (Eq. 1) assumes a 100 % conversion 20 from sulphur to SO 2 during combustion, which is only true for an idealised combustion process. There is a range of uncertainty of how much sulphur is oxidised and how much is released as particles. Studies found that there could be an underestimation of the 11038 Introduction

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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | sulphur fuel content between 1-19 % from assuming complete conversion (Schlager et al., 2006;Agrawal et al., 2008;Moldanova et al., 2009;Balzani Lööv et al., 2014). The uncertainty of our measurements is a combination of the calibration uncertainty and the uncertainty resulting from the signal to noise ratio (SNR). CO 2 values with a SNR of less than five are excluded from the data, which leads to an upper limit 5 uncertainty of 20 %. However, the majority of CO 2 values has an uncertainty of around 10 %. For SO 2 we do not exclude data with a low SNR because these are the zero sulphur content cases. The SNR of SO 2 data for a sulphur content of around 0.1 % is 10 or better, with a decrease for lower sulphur content values. For an SNR below 5 we consider the SO 2 signal as zero. This is only important for the January 2015 data, since 10 the measured SO 2 concentrations in 2015 are much lower than for the 2014 data. This is shown in Fig. 2 as a comparison between one week in December 2014 and one week in January 2015 with similar weather conditions. While no reduction in NO values can be observed, there is a large reduction in SO 2 values as expected.
All uncertainties added up with the root of sum of squares method, this gives us an 15 uncertainty range for the sulphur content calculations of 15-30 %.

Results
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 20 set is the so called pre-regulation-change set, with an allowed sulphur fuel content for the ships of 1.0 %. The January 2015 data set consists of 589 ship plumes of 374 individual ships which since the 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 % sul- 25 phur limit with respect to the measurement uncertainty. This is better than previously published compliance rates at other locations of 85 % of 174 ship plumes, although it should be noted that this study did not include uncertainty considerations (Beecken et al., 2014a), 90 % of 255 ship plumes and 97 % of 211 ship plumes (Beecken et al., 2014b). However, a study of Diesch et al., 2013, that describes measurements with a mobile laboratory along the Elbe River near our measurement site, found for 139 ship plumes a compliance of nearly 100 %. This could possibly be credited to the spe-5 cial 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 % sulphur limit in a legally binding way above the value of 0.149 %, we suggest to use 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 15 ships measured in January 95.4 % were complying with the new regulation.
Color-coded in the Figs. 3 and 4 are the lengths of the ships in 50 m size steps. Even before the regulation change ships smaller than 100 m did not use fuel with sulphur values higher than 0.2 %, most likely because their engines cannot process such fuels or storage capacity for two different kinds of fuels is not available. After the regulation 20 change, those smaller ships still do not use the fuels that reach up to the allowed 0.1 % limit. If one considers only those ships larger than 100 m that could choose which fuel to use and had to change their way of operation, the compliance drops to 93 %.
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 25 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. detect about 30-40 % of those events, for month with unfavourable wind conditions like November 2014, this value drops to less than 10 %.

Conclusions
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 sulphur fuel content regula- 5 tions. 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 10 a large data set on fuel usage of ships of altogether 1413 analysed ship plumes. This includes the first data after the most recent regulation change in the North Sea SECA, where fuel sulphur content limits were reduced from 1 to 0.1 % on 1 January 2015.
Our data shows that the vast majority (95.4 %) of ships measured are indeed complying with the new regulation of 0.1 % sulphur fuel content. Compliance has dropped 15 slightly compared to the value of more than 99 % observed for the 1 % sulphur limit in fall 2014. It should be noted that the global oil price and thus MGO costs for the needed sulphur quality in January 2015 was the lowest since 2009, but we hope that not only economic issues influence the decision whether to comply with environmental legislation or not.