Subscriber access provided by UNIV OF TEXAS DALLAS
Energy and the Environment
Particulate mass and non-volatile particle number emissions from marine engines using low-sulfur fuels, natural gas or scrubbers Kati Lehtoranta, Päivi Tellervo Aakko-Saksa, Timo Murtonen, Hannu Vesala, Leonidas Ntziachristos, Topi Rönkkö, Panu Karjalainen, Niina Kuittinen, and Hilkka Timonen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b05555 • Publication Date (Web): 19 Feb 2019 Downloaded from http://pubs.acs.org on February 27, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 28
Environmental Science & Technology
1
Particulate mass and non-volatile particle number
2
emissions from marine engines using low-sulfur
3
fuels, natural gas or scrubbers
4
Kati Lehtoranta1*, Päivi Aakko-Saksa1, Timo Murtonen1, Hannu Vesala1, Leonidas
5
Ntziachristos2, Topi Rönkkö2, Panu Karjalainen2, Niina Kuittinen2, Hilkka Timonen3
6
1VTT
Technical Research Centre of Finland, P.O.Box 1000, FI-02044 VTT, Finland, 2Tampere
7
University of Technology, P.O. Box 692, FI-33101, Finland, 3Finnish Meteorological Institute,
8
P.O.Box 503, FI-00101 Helsinki, Finland
9
10
ABSTRACT
11
In order to meet stringent fuel sulfur limits, ships are increasingly utilizing new fuels or,
12
alternatively, scrubbers to reduce sulfur emissions from the combustion of sulfur-rich heavy fuel
13
oil. The effects of these methods on particle emissions are important, since particle emissions from
14
shipping traffic are known to have both climatic and health effects. In this study, the effects of
15
lower sulfur level liquid fuels, natural gas (NG), and exhaust scrubbers on particulate mass (PM)
16
and non-volatile particle number (PN greater than 23 nm) emissions were studied by measurements
17
in laboratory tests and in-use. The fuel change to lower sulfur level fuels or to NG and the use of
ACS Paragon Plus Environment
1
Environmental Science & Technology
Page 2 of 28
18
scrubbers significantly decreased the PM emissions. However, this was not directly linked with
19
non-volatile PN emission reduction, which should be taken into consideration when discussing the
20
health effects of emitted particles. The lowest PM and PN emissions were measured when utilizing
21
NG as fuel, indicating that the use of NG could be one way to comply with up-coming regulations
22
for inland waterway vessels. Low PN levels were associated with low elemental carbon. However,
23
a simultaneously observed methane slip should be taken into consideration when evaluating the
24
climatic impacts of NG-fueled engines.
25
Abstract Art
26 27
INTRODUCTION
28
Shipping is a very efficient way of transporting goods, and currently the majority of global
29
trade volumes is transported by sea. Although significant reductions in emissions of terrestrial
30
vehicle engines have been achieved due to a series of environmental regulations and subsequent
31
implementation of emission control techniques over the years, marine vessel emissions have not
32
been thoroughly addressed. As a result, their relative contribution to air pollution has increased
33
during recent years 1.
ACS Paragon Plus Environment
2
Page 3 of 28
Environmental Science & Technology
34
Container ships, bulk carriers and oil tankers, with slow-speed 2-stroke engines, consumed
35
approx. 74% of all marine fuels in 2015, whereas ships having medium-speed 4-stroke engines
36
(like most cruise ships) consumed approx. 23%2. However, compared to containers and cargo
37
vessels, cruise ship routes are generally nearer to coastlines, and these ships may spend more
38
time at anchor or berthing, which can have a significant effect on local air quality.
39
Around 15% of global anthropogenic NOx and 5-8% of global SOx emissions can be attributed
40
to shipping operations 3–5. In response, the International Maritime Organization (IMO) has
41
introduced specific regulations to reduce shipping emissions of both pollutants. NOx limits have
42
been set at a global level with Tier I and II standards, whereas lower limits are applicable to
43
ships constructed after 2016 (Tier III) in NOx emission control areas (NECA). Tier III leads to an
44
increase in the use of emission control devices, the most important of which is selective catalytic
45
reduction (SCR). The SCR system utilizes a catalyst and externally fed ammonia to reduce NOx
46
emissions. Catalysts in ship applications are usually vanadium-based, and an aqueous solution of
47
urea is utilized as a source of ammonia (see, for example 6,7).
48
In order to address SOx emissions, a global cap in fuel sulfur content (FSC) of marine fuels has
49
been set at 0.5% m/m by 2020, compared to earlier permitted FSC levels of up to 3.5% m/m. In
50
SOx emission control areas (SECA), the FSC is further limited to 0.1 %. Higher sulfur levels are
51
applicable only if an on-board sulfur scrubber is used. Different types of SOx scrubbers use fresh
52
water (closed loop), seawater (open loop), a hybrid technology (either fresh or sea water), or dry
53
removal agents. Alternatively, distillate fuels (ISO 8217), alcohols and biofuels, or gaseous fuels
54
– primarily liquefied natural gas (LNG) with inherently low FSC, may be used for compliance
55
with sulfur regulations. Of the distillate fuels, marine gas oil (MGO, free from residual fuel) is
56
primarily used in marine engines with displacement below 5 liters per cylinder, whereas marine
ACS Paragon Plus Environment
3
Environmental Science & Technology
57
diesel oil (MDO, may have traces of residual fuel) is typically used in engines with over 5 liters
58
per cylinder. In addition, low sulfur residual marine fuel oils (also called hybrid fuels) may be
59
utilized in ships operating in SECAs.
Page 4 of 28
60
The IMO has not defined explicit emission limits for PM, despite its environmental and health
61
implications. Shipping PM emissions are important especially in Asia, with China having 7 of the
62
10 largest ports in the world in terms of volume of transported goods8. Liu et al.9 recently showed
63
that during ship plume-influenced periods, shipping emissions contributed up to 20–30% of total
64
PM2.5 within tens of kilometers of the coastal and riverside Shanghai regions. Chen et al.10
65
estimated that the contribution of shipping emissions to ambient PM2.5 concentrations over the
66
urban area of Qingdao could exceed 20%. Corbett et al.5 estimated that on a global scale, shipping-
67
related PM emissions are annually responsible for approximately 60 000 premature deaths related
68
to cardiopulmonary and lung cancer diseases. Sofiev et al.11 recently estimated that total premature
69
mortality due to shipping is much higher, and that even low-sulfur marine fuels still account for
70
approximately 250 000 deaths annually. SOx regulations also have an implicit impact on PM, since
71
they lead to decreased particulate sulfate emissions. A recent study by Sofiev et al.11 showed that
72
low-sulfur fuels may provide pollution health benefits but with a climate trade-off, since the
73
reduction in sulfate in PM decreases the climatic cooling effects of the exhaust aerosol. Although
74
sulfate aerosol has a cooling effect, absorbent black carbon (BC) emissions warm the atmosphere
75
and are not explicitly dependent on the FSC12. BC deposition on ice and subsequent albedo change
76
is especially important in the Arctic area, which has recently experienced an increase in shipping
77
activity13.
78
The existing evidence discussed above suggests that global shipping PM emissions have a clear
79
effect on climate, air pollution and public health. PM emission levels are also significantly
ACS Paragon Plus Environment
4
Page 5 of 28
Environmental Science & Technology
80
influenced by regulations addressing other pollutants. The present study provides evidence on how
81
different options enabling ships to operate within SECAs affect the PM emissions of marine
82
engines. The options examined include lower sulfur level fuels (liquid and gaseous) as well as on-
83
board scrubbers. Both the PM and non-volatile PN emissions are studied in experiments conducted
84
on board two different ships and in a marine engine laboratory.
85 86
EXPERIMENTAL
87
Engines in laboratory
88
Experiments with low-sulfur liquid fuels and natural gas were conducted in the marine engine
89
laboratory. The first engine was a Wärtsilä Vasa 4R32, a four-cylinder medium-speed 4-stroke
90
marine engine that was retrofitted to enable operation with natural gas in dual fuel (DF) mode. In
91
this mode, a small quantity of liquid fuel is first injected to pilot combustion, which is then
92
sustained by delivery of the main quantity of natural gas. The maximum power of this engine
93
was 1400 kW. The engine was modified to run on natural gas in 2016, using state-of-the-art
94
components of current commercial natural gas marine engines. The modification of the engine
95
included, for example, installing gas admission valves on the cylinder heads and replacing the
96
cylinder heads as well as the liners, pistons, camshaft and turbocharger. In addition, the engine
97
control system was updated and a pilot fuel line with a high-pressure pilot fuel pump was added.
98
This engine was tested with the 40% and 85% loads that are considered representative of in-
99
harbor maneuvering and open-seas operation, respectively. Emissions of PM and PN were also
100
characterized from a second DF engine on the test bed. This was a 2017 production series
ACS Paragon Plus Environment
5
Environmental Science & Technology
Page 6 of 28
101
Wärtsilä 20DF (medium speed, 4-stroke engine), which is of similar size to the 4R32 engine and
102
delivers a maximum power output of 1000 kW.
103
Engines and scrubbers on board
104
Emission measurements were also made on board two ships during regular cruising conditions.
105
A modern cruise ship equipped with SCR and a hybrid sulfur scrubber was first tested. The
106
hybrid scrubber used closed loop during harbor operation, whereas sea water scrubbing was used
107
on the open sea. PM and PN emissions were measured from two main engines (E1, E2) at
108
constant engine loads of 40% and 75%. Both engines were medium-speed, 4-stroke, modern
109
engines. For E1, the measurements were made upstream (engine outlet) and downstream of the
110
scrubber. The E2 engine was equipped with the SCR placed upstream of the scrubber, so the
111
measurement points were downstream of the scrubber and downstream of the SCR, before the
112
scrubber. The second ship was a RoPax vessel (built for freight vehicle transport along with
113
passenger accommodation) equipped with a diesel oxidation catalyst (DOC) and an open loop
114
seawater-operating scrubber. PM and PN from one of its main engines (a medium-speed, 4-
115
stroke engine, E3) were measured upstream of the scrubber (thus downstream of the DOC) and
116
downstream of the scrubber. The ship operated normally and the engine load varied during the
117
cruise mainly in the range of 63-66% of maximum load. A schematic layout of all tested engines
118
and related after-treatment is presented in supporting information (Figure S1).
119
Fuels
120
Table 1 contains the main specifications of all liquid fuels used in the measurement campaigns.
121
Two different liquid fuels (MDO, MGO) were used in the laboratory experiments with the
122
Wärtsilä Vasa 4R32 engine when operated in liquid-fuel mode. The MDO had an FSC of
ACS Paragon Plus Environment
6
Page 7 of 28
Environmental Science & Technology
123
0.0822% and thus fulfilled the SECA requirements (limit 0.1% S), whereas the MGO was of
124
even higher quality (on-road diesel quality, EN 590), with a very low sulfur level. High quality
125
MGO with a very low sulfur level is not widely utilized in ships today, but it was selected here
126
based more on its role as a pilot in DF mode. In DF mode, the main fuel was compressed natural
127
gas (CNG) and the pilot injection was with MGO according to the engine manufacturer’s
128
instruction. The CNG had a high methane content (volumetric composition 96.4% methane, 2.3
129
% ethane, 0.35 % propane, 0.15% other hydrocarbons, 0.57% nitrogen and 0.21% carbon
130
dioxide). In DF mode, the pilot fuel quantity was adjusted to 1.2 % and 3.8 % of the total fuel
131
mass flow for 85% and 40% loads, respectively. LNG was used as the main fuel in the 20DF
132
engine, since there was no natural gas distribution system available for that engine. The LNG
133
used contained 90% methane and approximately 9% ethane. MGO was also used as pilot in this
134
case, with an amount of approximately 2% of the total fuel mass flow for 75% engine load.
135
The cruise ship, equipped with a scrubber to meet SECA requirements, operated on heavy-fuel
136
oil (HFO) with 0.65% sulfur content as a fuel (in all its engines). For comparison, the E2 engine
137
was also operated on 0.10% FSC MGO for a period of nine hours with 40% load to conduct
138
emission measurements. The RoPax ship operated on 1.9% FSC HFO.
139
Table 1 Main specifications of liquid fuels used in the measurement campaigns.
Parameter
Unit
Use Engine Density (15°C) Viscosity (40°C) Heating value. lower Flash point
kg/m3 mm2/s MJ/kg °C
MGO
MDO
HFO
MGO
HFO
< 0.001 % S
< 0.1 % S
< 0.7 % S
< 0.1 % S
23nm concentrations
178
were determined with an Airmodus A23 Condensation Particle Counter (CPC). The DR setting
179
in the case of non-volatile PN sampling is much less critical than in the case of PM mass, due to
180
the elimination of condensation dynamics in the former case. The relatively high DR, which is
181
recommended for road vehicles, was also adopted in this study to decrease coagulation dynamics
ACS Paragon Plus Environment
9
Environmental Science & Technology
Page 10 of 28
182
and the corresponding PN concentration sensitivity to residence time before counting 19. The DR
183
setting would be even less relevant if non-volatile PM rather than PN was to be characterized, as
184
in the case of jet exhaust sampling, where DRs as low as 10 are being implemented 20.
185
The concentrations of NOx (NO and NO2) in exhaust emissions were measured with a
186
chemiluminescence detector (CLD), and carbon monoxide (CO) and carbon dioxide (CO2) with
187
a non-dispersive infrared (NDIR) analyzer. Light hydrocarbon components were speciated with a
188
gas chromatograph when natural gas was used as a fuel. A Flame Ionization Detector (FID) was
189
utilized in some of the tests to measure the total hydrocarbon (THC) content in the exhaust.
190
Concentrations of sulfur dioxide (SO2) and water were measured with FTIR (Fourier Transform
191
Infrared spectroscopy).
192
RESULTS AND DISCUSSION
193
PM and PN emissions
194
Liquid fuels
195
HFO was the fuel of choice for the majority of shipping operations before the global sulfur cap
196
enforcement. In addition to high FSC, this fuel may contain large amounts of metals, such as V
197
and Ni, and other ash components, compared to distillate fuels that contain practically no metals
198
or ash (Table 1). Earlier experiments performed on the same Vasa 4R32 engine used in the
199
current study demonstrated that marine engine PM emissions depend heavily on fuel quality. At
200
75% load, PM decreased from 850 mg/kWh, when using 2.5% FSC HFO, to 280 mg/kWh with
201
1% FSC HFO12, and down to 60 mg/kWh when using a light fuel oil (similar to MGO in the
202
present study)14.
ACS Paragon Plus Environment
10
Page 11 of 28
Environmental Science & Technology
203
The present results confirm previous evidence. Figure 1a presents PM emissions of the two
204
laboratory engines fueled with NG, MDO and MGO on the test bed. PM with MGO at 85% load
205
was at a similar level to what has been measured previously at 75% load14. Earlier evidence
206
using HFO has shown that sulfate and associated water comprise more than half of total PM12,21.
207
With the lighter fuels used in the present study, sulfate accounted for only a minor fraction of
208
total PM (Figure 1b); even in the case of MDO the sulfate comprised only 4% of the total PM in
209
the 85% load case. EC (18-19% of total PM) and OC (60-63% of PM) comprised the majority of
210
PM for MDO and MGO. The ‘rest’ PM fractions were calculated by subtracting the EC, OC and
211
sulfate amounts from the total PM. This ‘rest’ fraction was not further specified in the present
212
study, but typically it is comprised of water as well as fuel and lube-derived ash.
213 214
Figure 1 a) PM and c) non-volatile PN>23nm emissions measured from 40% load mode and 85%
215
load mode with the 4R32 DF engine utilizing MDO, MGO and NG fuels and from 75% load with
216
the 20DF engine utilizing MGO and LNG fuels (marked load 75% p). Error bars show the standard
217
deviation of a minimum of five measurements; b) the PM composition of exhaust of the 4R32 DF
218
engine fueled with MDO, MGO and NG at 85% load.
ACS Paragon Plus Environment
11
Environmental Science & Technology
Page 12 of 28
219
The particle emission results also show that the MGO produced 17-25% less PM than the
220
MDO, but without any measurable effects on PN>23nm (see Figure 1c). Other studies (e.g. 21–24)
221
concluded that liquid fuel change has the potential to decrease particle emissions from ships,
222
although they also concluded that such reductions are not only due to FSC reduction.
223
Additionally, even if reduced sulfur content of the fuel efficiently reduced the PM emission, the
224
BC emissions were not necessarily reduced12. Khan et al.22 and Zetterdahl et al.23 both compared
225
emissions of HFO (higher S) to a lower sulfur level fuel. They both observed significant
226
reductions in PM mass when changing to lower sulfur content fuel. Zetterdahl et al. observed
227
67% reduction in PM mass and smaller average particle size when changing to low sulfur level
228
fuel, but the total particle number was found to be on similar levels for both fuels. In the present
229
study, we also showed a PM decrease with fuel sulfur decrease, although no difference was
230
found in the PN level.
231
Effect of engine load
232
Engine load was found to affect the work-specific PM emissions for the laboratory engine 4R32.
233
PM emissions at low load (40%) were higher than when the load was increased, with all of the
234
fuels used. Emission rates at low load were also more variable than at higher load, as indicated by
235
the error bars in Figure 1a. In DF operation, the quantity of liquid fuel used per unit of energy was
236
higher at low load (3.8 % of main fuel) compared to high load (1.2 % of main fuel), which may
237
have contributed to the higher energy-specific PM emissions at low load. Marine engines are
238
generally optimized for loads in the 75-90% range, which is the typical operation range for open-
239
seas sailing. In ports, low loads are required for manoeuvring and for berthing. Although in-port
240
emissions make only a small contribution to the total emissions of any vessel, they are important
241
for local air quality and associated health effects on populations in the vicinity of ports 25. This
ACS Paragon Plus Environment
12
Page 13 of 28
Environmental Science & Technology
242
means that any future regulation initiatives on PM emissions control from ships will require that
243
emissions are also regulated at low load operation.
244
Natural gas
245
DF operation (with NG as main fuel) resulted in the lowest PM levels for both engines, at a
246
level 63-69% lower than the MGO and 72-75% lower than the MDO. When shifting to DF
247
operation, only traces of EC were observed and OC accounted for 83% of PM (Figure 1b). The
248
impact of NG use was actually magnified when non-volatile PN>23nm was considered, with PN
249
levels 98-99% lower than when using liquid fuels (Figure 1c). Particles in this size range are
250
often assumed to represent the soot mode that accounts for the major part of EC. The observed
251
low PN>23nm for NG is consistent with the very low levels of EC measured for this particular fuel.
252
The low soot emissions with NG also explain why changes in the load when in DF mode (85%
253
load compared to 40% load with the 4R32 engine, Figure 1c) had practically no effect on the
254
non-volatile particle number, which is different from what is observed with liquid fuels.
255
Differences under DF mode are observed when comparing the retrofitted engine with the
256
production-series engines; the latter were significantly lower in terms of both PM and PN>23nm
257
emissions than the retrofitted engine. In addition to the impact of engine design, load level, and
258
NG composition differences between the two engines, the lubricating oil might be a significant
259
contributor to the observed differences, as observed in previous studies26–29. The two engines
260
operated with lubricating oils of different specifications and, presumably, different consumption
261
rates, although lubrication oil consumption was not measured in any of the engines. There were
262
also differences in the pilot fuel amounts (i.e. 2% pilot fuel injection at 75% load of the
263
production series engines compared to the 1.2% ratio used at 85% load of the retrofitted engine),
ACS Paragon Plus Environment
13
Environmental Science & Technology
264
but these do not provide an explanation for the observed lower PN>23nm emissions of the
265
production engine.
Page 14 of 28
266
PN>23nm discussion
267
The level of PN>23nm emissions from marine engines is important in view of the upcoming EU
268
regulations for inland waterway vessels. The Stage V regulation, applicable from 2020 on, has
269
introduced the requirement of PN>23nm remaining below 1012 kWh1 over a testing procedure
270
involving several steady-state modes and weighing factors. Although we have not tested the
271
complete range of conditions required by the regulation, the orders of magnitude of PN collected
272
are indicative of the potential of different technology options.
273
PN>23nm emissions were well beyond the limit with all of the tested liquid fuels, almost two
274
orders of magnitude or higher than the limit, with both engines tested. The retrofitted engine
275
(with NG as the main fuel) produced 1.1×1012 kWh1 and 1.0×1012 kWh1 at 85% and 40% load,
276
respectively, thus being within the range of regulatory requirements. The PN>23nm emissions of
277
the production-series engine at 75% load with LNG was 1.3×1011 kWh1, which was actually
278
much lower than the limit (1012 kWh1). These results indicate that the use of natural gas as a fuel
279
for marine and inland waterway vessels could be one way to comply with upcoming regulations.
280
The low non-volatile PN>23nm level is also associated with low EC concentration (seen Figure 1).
281
This strongly indicates that the regulation of PN>23nm may also be effective in controlling EC
282
(and, correspondingly, BC) emissions of vessels and may thus contribute to decreasing the
283
shipping impact on climate forcing. Figure 1c shows that light liquid fuel effects on PN>23nm
284
were more marginal.
ACS Paragon Plus Environment
14
Page 15 of 28
285
Environmental Science & Technology
The observations related to fuel effects on PN>23nm emissions in this study refer to non-volatile
286
particles above 23 nm in size and could be different if smaller particles and/or semi-volatile
287
particles were included in the analysis. Anderson et al. 28 studied total particle emissions from an
288
LNG-powered ship and also observed that LNG resulted in significantly lower PN numbers than
289
when MGO was used. However, they also found that a significant fraction of particles were in
290
the sub-23 nm size range. Alanen et al. 29 observed a remarkable amount of sub-23 nm
291
nanoparticles with diameters down to only a few nm when using NG. Marine exhaust PN
292
conclusions should therefore be observed carefully in relation to the particle population to which
293
they refer.
294
Scrubbers on board
295
The results of PM and PN>23nm measurements conducted on board the two different ships are
296
presented in Figure 2. The PM level from the E3 engine (RoPax ship) during regular vessel
297
operation with the engine load varying between 63% and 66% was the highest. In this case, the
298
FSC of the HFO used was significantly higher than that of the HFO used on the cruise ship
299
(engines E1 and E2). Operation of the scrubber was found to decrease the PM level by 21-45%
300
in the high load cases (E1, E2, E3, loads 63-66% and 75%) and 8-17% at low load (40%, E1 and
301
E2). The PM composition analysis (Figure 2b) showed that the organic carbon was reduced by
302
the scrubber. Interestingly, sulfate aerosol was at the same level both upstream and downstream
303
of the scrubber, whereas EC seemed to be decreased by passage over the scrubber. The ‘rest’ part
304
of PM (consisting typically of sulfate-associated water and ash) was almost halved by the
305
scrubber.
ACS Paragon Plus Environment
15
Environmental Science & Technology
Page 16 of 28
306 307
Figure 2 a) PM and c) non-volatile PN>23nm emissions measured on board two different ships (i.e.
308
engines E1 and E2 on a cruise ship, E3 on a RoPax); b) PM composition from measurements made
309
on engine E1 at 75% load. Note: In the case of engine E3 the HFO differed from the HFO utilized
310
with engines E2 and E1 (see Table 1).
311
The impact of the scrubber on PM emitted from the E1 and E2 engines was different, despite
312
the fact that both engines were on the same ship and utilizing same scrubber. One reason for this
313
is that sampling from the E2 was conducted downstream of the SCR to which the engine was
314
connected. First, the SCR by itself was most probably having a positive impact on PM emissions.
315
The SCR system has been shown to have an impact on PM e.g. by decreasing the organic
316
fraction6. The additional benefit that the scrubber can offer is therefore lower than the
317
improvement it offers over engine-out PM emissions.
318
Even though PM clearly decreased over the scrubber, its effect on the non-volatile PN was less
319
clear. In the case of E1, the PM decrease was 41% in 75% load mode, whereas there was
320
practically no change in the PN>23nm level. On the other hand, in the case of E2 and 75% load, the
ACS Paragon Plus Environment
16
Page 17 of 28
Environmental Science & Technology
321
PM decrease was 21% and the PN>23nm decrease was observed to be 30%. However, bearing in
322
mind the fact that the standard deviation for PN measurements made in the laboratory (with
323
MDO fuel) was ±15-18%, this PN decrease is considered to be minor.
324
Use of MGO in engine E2 led to lower PM and PN>23nm concentrations than were observed
325
downstream of the scrubber with HFO fuel. However, this is only one example (one MGO fuel,
326
one engine, one load mode) and cannot be presented as a general conclusion.
327
Fridell & Salo30 also studied the particle emissions from a marine engine equipped with a
328
scrubber (open-loop wet scrubber using seawater). They found the total number of particles to be
329
reduced by 92% in the scrubber, while the solid fraction was reduced by 48%. The PM was also
330
significantly decreased, i.e. about 75% of the total PM was captured by the scrubber. These are
331
all higher reduction values than in the present study and there might be several reasons for this,
332
e.g. differences in engines, fuels and/or scrubbers. Moreover, one big difference is the particle
333
measurement method. Fridell & Salo measured the PN with an Engine Exhaust Particle Sizer
334
with a size range of 5.6 - 560 nm therefore also covering particles below 23 nm size, which were
335
not measured in the present study. Several studies performed with liquid fuels report particle size
336
distributions from marine engines suggesting that a share of non-volatile PN resides below the 23
337
nm level28,31–33. In addition to the PN 23 nm limit, the results of Ntziachristos et al.14,21 show that
338
even when conducted following the ISO 8178 protocol, the dilution system can have a
339
significant effect on the measured PM result. At minimum, the dilution ratio range allowed
340
should be more strictly defined in order to obtain comparable results.
341
To the authors’ knowledge, the standard PM and non-volatile PN measurement methods were
342
utilized for the first time in the present study in studying ship emissions with different fuels and
ACS Paragon Plus Environment
17
Environmental Science & Technology
Page 18 of 28
343
after-treatment systems. Furthermore, the dilution conditions were strictly controlled in order to
344
make comparison of the results of different measurement campaigns possible both on board and
345
in engine laboratories.
346
Gaseous exhaust emissions
347
Liquid fuels and natural gas
348
With the laboratory engine (4R32), gaseous emissions were also studied (Table 2). Lower
349
levels of NOx were measured with NG compared to MGO or MDO. This was most probably due
350
to the homogenous premixing of the gas with air and the lower combustion temperature of NG
351
(in lean burn conditions). As expected, no SO2 was detected in the exhaust gas when utilizing
352
either NG or MGO (23) measurement system
425 426
AUTHOR INFORMATION
427
Corresponding Author
428
*E-mail
[email protected]; phone +358 407236703
429
Author Contributions
430
The manuscript was written through contributions of all authors. All authors have given approval
431
to the final version of the manuscript.
432
ACKNOWLEDGMENT
433
This study was part of several projects: HERE, SEA-EFFECTS BC and INTENS, funded by
434
Business Finland and several Finnish companies, and Hercules-2 with funding from the
435
European Union’s Horizon 2020 research and innovation programme under grant agreement No.
436
634135.
437
REFERENCES
438
(1)
439
Viana, M.; Hammingh, P.; Colette, A.; Querol, X.; Degraeuwe, B.; Vlieger, I. de; van Aardenne, J. Impact of Maritime Transport Emissions on Coastal Air Quality in Europe.
ACS Paragon Plus Environment
22
Page 23 of 28
Environmental Science & Technology
Atmos. Environ. 2014, 90, 96–105. https://doi.org/10.1016/j.atmosenv.2014.03.046.
440 441
(2)
AND FUEL USE IN GLOBAL SHIPPING 2015; 2017.
442 443
Comer, B.; Olmer, N.; Mao, X.; Roy, B.; Rutherford, D. A. N. BLACK CARBON EMISSIONS
(3)
Viana, M.; Hammingh, P.; Colette, A.; Querol, X.; Degraeuwe, B.; Vlieger, I. de; van
444
Aardenne, J. Impact of Maritime Transport Emissions on Coastal Air Quality in Europe.
445
Atmos. Environ. 2014, 90, 96–105. https://doi.org/10.1016/J.ATMOSENV.2014.03.046.
446
(4)
1. The Last 50 Years. 2005, 110, 1–12.
447 448
Eyring, V.; Kohler, H. W.; van Aardenne, J.; Lauer, A. Emissions from International Shipping:
(5)
Corbett, J. J.; Winebrake, J. J.; Green, E. H.; Kasibhatla, P.; Eyring, V.; Lauer, A. Mortality
449
from Ship Emissions: A Global Assessment. Environ. Sci. Technol. 2007, 41 (24), 8512–8518.
450
https://doi.org/10.1021/es071686z.
451
(6)
Lehtoranta, K.; Vesala, H.; Koponen, P.; Korhonen, S. Selective Catalytic Reduction
452
Operation with Heavy Fuel Oil: NO
453
2015, 49 (7), 4735–4741. https://doi.org/10.1021/es506185x.
454
(7)
X
, NH 3 , and Particle Emissions. Environ. Sci. Technol.
Magnusson, M.; Fridell, E.; Ingelsten, H. H. The Influence of Sulfur Dioxide and Water on
455
the Performance of a Marine SCR Catalyst. Appl. Catal. B Environ. 2012, 111–112, 20–26.
456
https://doi.org/10.1016/j.apcatb.2011.09.010.
457
(8)
Zhang, Y.; Yang, X.; Brown, R.; Yang, L.; Morawska, L.; Ristovski, Z.; Fu, Q.; Huang, C.
458
Shipping Emissions and Their Impacts on Air Quality in China. Sci. Total Environ. 2017, 581–
459
582, 186–198. https://doi.org/10.1016/J.SCITOTENV.2016.12.098.
460 461
(9)
Liu, Z.; Lu, X.; Feng, J.; Fan, Q.; Zhang, Y.; Yang, X. Influence of Ship Emissions on Urban Air Quality: A Comprehensive Study Using Highly Time-Resolved Online Measurements and
ACS Paragon Plus Environment
23
Environmental Science & Technology
Page 24 of 28
462
Numerical Simulation in Shanghai. Environ. Sci. Technol. 2017, 51 (1), 202–211.
463
https://doi.org/10.1021/acs.est.6b03834.
464
(10)
Chen, D.; Wang, X.; Nelson, P.; Li, Y.; Zhao, N.; Zhao, Y.; Lang, J.; Zhou, Y.; Guo, X. Ship
465
Emission Inventory and Its Impact on the PM2.5 Air Pollution in Qingdao Port, North China.
466
Atmos. Environ. 2017, 166, 351–361. https://doi.org/10.1016/J.ATMOSENV.2017.07.021.
467
(11)
Sofiev, M.; Winebrake, J. J.; Johansson, L.; Carr, E. W.; Prank, M.; Soares, J.; Vira, J.;
468
Kouznetsov, R.; Jalkanen, J.-P.; Corbett, J. J. Cleaner Fuels for Ships Provide Public Health
469
Benefits
470
https://doi.org/10.1038/s41467-017-02774-9.
471
(12)
with
Climate
Tradeoffs.
Nat.
Commun.
2018,
9
(1),
406.
Aakko-Saksa, P.; Murtonen, T.; Vesala, H.; Koponen, P.; Nyyssönen, S.; Puustinen, H.;
472
Lehtoranta, K.; Timonen, H.; Teinilä, K.; Karjalainen, P.; et al. Black Carbon Measurements
473
Using Different Marine Fuels. 28th CIMAC World Congr. 2016, Paper 068.
474
(13)
Winther, M.; Christensen, J.; Plejdrup, M.; Ravn, E.; Eriksson, O.; Kristensen, H. Emission
475
Inventories for Ships in the Arctic Based on Satellite Sampled AIS Data. Atmos. Environ.
476
2014, 91, 1–14. https://doi.org/10.1016/J.ATMOSENV.2014.03.006.
477
(14)
Ntziachristos, L.; Saukko, E.; Rönkkö, T.; Lehtoranta, K.; Timonen, H.; Hillamo, R.; Keskinen,
478
J. Impact of Sampling Conditions and Procedure on Particulate Matter Emissions from a
479
Marine Diesel Engine. 28th CIMAC World Congr. 2016, Paper 165.
480
(15)
Ristimaki, J.; Hellen, G.; Lappi, M. Chemical and Physical Characterization of Exhaust
481
Particulate Matter from a Marine Medium Speed Diesel Engine. 26th CIMAC World Congr.
482
2010, Paper 73.
483
(16)
Giechaskiel, B.; Maricq, M.; Ntziachristos, L.; Dardiotis, C.; Wang, X.; Axmann, H.;
ACS Paragon Plus Environment
24
Page 25 of 28
Environmental Science & Technology
484
Bergmann, A.; Schindler, W. Review of Motor Vehicle Particulate Emissions Sampling and
485
Measurement: From Smoke and Filter Mass to Particle Number. J. Aerosol Sci. 2014, 67,
486
48–86. https://doi.org/10.1016/J.JAEROSCI.2013.09.003.
487
(17)
Birch, M. E.; Cary, R. A. Elemental Carbon-Based Method for Monitoring Occupational
488
Exposures to Particulate Diesel Exhaust. Aerosol Sci. Technol. 1996, 25 (3), 221–241.
489
https://doi.org/10.1080/02786829608965393.
490
(18)
Aakko-Saksa, P.; Koponen, P.; Aurela, M.; Vesala, H.; Piimäkorpi, P.; Murtonen, T.; Sippula,
491
O.; Koponen, H.; Karjalainen, P.; Kuittinen, N.; et al. Considerations in Analysing Elemental
492
Carbon from Marine Engine Exhaust Using Residual, Distillate and Biofuels. J. Aerosol Sci.
493
2018, 126, 191–204. https://doi.org/10.1016/J.JAEROSCI.2018.09.005.
494
(19)
Isella, L.; Giechaskiel, B.; Drossinos, Y. Diesel-Exhaust Aerosol Dynamics from the Tailpipe
495
to
496
https://doi.org/10.1016/J.JAEROSCI.2008.04.006.
497
(20)
the
Dilution
Tunnel.
J.
Aerosol
Sci.
2008,
39
(9),
737–758.
Brem, B. T.; Durdina, L.; Siegerist, F.; Beyerle, P.; Bruderer, K.; Rindlisbacher, T.; Rocci-
498
Denis, S.; Andac, M. G.; Zelina, J.; Penanhoat, O.; et al. Effects of Fuel Aromatic Content on
499
Nonvolatile Particulate Emissions of an In-Production Aircraft Gas Turbine. Environ. Sci.
500
Technol. 2015, 49 (22), 13149–13157. https://doi.org/10.1021/acs.est.5b04167.
501
(21)
Ntziachristos, L.; Saukko, E.; Lehtoranta, K.; Rönkkö, T.; Timonen, H.; Simonen, P.;
502
Karjalainen, P.; Keskinen, J. Particle Emissions Characterization from a Medium-Speed
503
Marine Diesel Engine with Two Fuels at Different Sampling Conditions. Fuel 2016, 186,
504
456–465. https://doi.org/10.1016/j.fuel.2016.08.091.
505
(22)
Khan, M. Y.; Giordano, M.; Gutierrez, J.; Welch, W. A.; Asa-Awuku, A.; Miller, J. W.; Cocker,
ACS Paragon Plus Environment
25
Environmental Science & Technology
Page 26 of 28
506
D. R. Benefits of Two Mitigation Strategies for Container Vessels: Cleaner Engines and
507
Cleaner
508
https://doi.org/10.1021/es2043646.
509
(23)
Fuels.
Environ.
Sci.
Technol.
2012,
46
(9),
5049–5056.
Zetterdahl, M.; Moldanová, J.; Pei, X.; Pathak, R. K.; Demirdjian, B. Impact of the 0.1% Fuel
510
Sulfur Content Limit in SECA on Particle and Gaseous Emissions from Marine Vessels.
511
Atmos. Environ. 2016, 145, 338–345. https://doi.org/10.1016/j.atmosenv.2016.09.022.
512
(24)
Part D Transp. Environ. 2010, 15 (4), 204–211. https://doi.org/10.1016/j.trd.2010.02.003.
513 514
(25)
Cooper, D. A. Exhaust Emissions from Ships at Berth. Atmos. Environ. 2003, 37 (27), 3817– 3830. https://doi.org/10.1016/S1352-2310(03)00446-1.
515 516
Winnes, H.; Fridell, E. Emissions of NOX and Particles from Manoeuvring Ships. Transp. Res.
(26)
Jayaratne, E. R.; Meyer, N. K.; Ristovski, Z. D.; Morawska, L. Volatile Properties of Particles
517
Emitted by Compressed Natural Gas and Diesel Buses during Steady-State and Transient
518
Driving
519
https://doi.org/10.1021/es2026856.
520
(27)
Modes.
Environ.
Sci.
Technol.
2012,
46
(1),
196–203.
Bullock, D. S.; Olfert, J. S. Size, Volatility, and Effective Density of Particulate Emissions from
521
a Homogeneous Charge Compression Ignition Engine Using Compressed Natural Gas. J.
522
Aerosol Sci. 2014, 75, 1–8. https://doi.org/10.1016/j.jaerosci.2014.04.005.
523
(28)
Anderson, M.; Salo, K.; Fridell, E. Particle- and Gaseous Emissions from an LNG Powered
524
Ship.
525
https://doi.org/10.1021/acs.est.5b02678.
526 527
(29)
Environ.
Sci.
Technol.
2015,
49
(20),
12568–12575.
Alanen, J.; Saukko, E.; Lehtoranta, K.; Murtonen, T.; Timonen, H.; Hillamo, R.; Karjalainen, P.; Kuuluvainen, H.; Harra, J.; Keskinen, J.; et al. The Formation and Physical Properties of
ACS Paragon Plus Environment
26
Page 27 of 28
Environmental Science & Technology
528
the Particle Emissions from a Natural Gas Engine. Fuel 2015, 162, 155–161.
529
https://doi.org/10.1016/j.fuel.2015.09.003.
530
(30)
Fridell, E.; Salo, K. Measurements of Abatement of Particles and Exhaust Gases in a Marine
531
Gas Scrubber. Proc. Inst. Mech. Eng. Part M J. Eng. Marit. Environ. 2014, 230 (1), 154–162.
532
https://doi.org/10.1177/1475090214543716.
533
(31)
Kasper, A.; Aufdenblatten, S.; Forss, A.; Mohr, M.; Burtscher, H. Particulate Emissions from
534
a Low-Speed Marine Diesel Engine. Aerosol Sci. Technol. 2007, 41 (1), 24–32.
535
https://doi.org/10.1080/02786820601055392.
536
(32)
Pirjola, L.; Pajunoja, A.; Walden, J.; Jalkanen, J.-P.; Rönkkö, T.; Kousa, A.; Koskentalo, T.
537
Mobile Measurements of Ship Emissions in Two Harbour Areas in Finland. Atmos. Meas.
538
Tech. 2014, 7 (1), 149–161. https://doi.org/10.5194/amt-7-149-2014.
539
(33)
Amanatidis, S.; Ntziachristos, L.; Karjalainen, P.; Saukko, E.; Simonen, P.; Kuittinen, N.;
540
Aakko-Saksa, P.; Timonen, H.; Rönkkö, T.; Keskinen, J. Comparative Performance of a
541
Thermal Denuder and a Catalytic Stripper in Sampling Laboratory and Marine Exhaust
542
Aerosols.
543
https://doi.org/10.1080/02786826.2017.1422236.
544
(34)
Aerosol
Sci.
Technol.
2018,
52
(4),
420–432.
Hesterberg, T. W.; Lapin, C. A.; Bunn, W. B. A Comparison of Emissions from Vehicles
545
Fueled with Diesel or Compressed Natural Gas. Environ. Sci. Technol. 2008, 42 (17), 6437–
546
6445. https://doi.org/10.1021/es071718i.
547
(35)
Liu, J.; Yang, F.; Wang, H.; Ouyang, M.; Hao, S. Effects of Pilot Fuel Quantity on the
548
Emissions Characteristics of a CNG/diesel Dual Fuel Engine with Optimized Pilot Injection
549
Timing.
Appl.
Energy
2013,
110,
201–206.
ACS Paragon Plus Environment
27
Environmental Science & Technology
https://doi.org/10.1016/j.apenergy.2013.03.024.
550 551
Page 28 of 28
(36)
Lehtoranta, K.; Murtonen, T.; Vesala, H.; Koponen, P.; Alanen, J.; Simonen, P.; Rönkkö, T.;
552
Timonen, H.; Saarikoski, S.; Maunula, T.; et al. Natural Gas Engine Emission Reduction by
553
Catalysts.
554
https://doi.org/10.1007/s40825-016-0057-8.
555
(37)
(38)
560
Sci.
Technol.
2017,
3
(2),
142–152.
Järvi, A. Methane Slip Reduction in Wärtsilä Lean Burn Gas Engines. 26th CIMAC World
Hiltner, J.; Loetz, A.; Fiveland, S. Unburned Hydrocarbon Emissions from Lean Burn Natural Gas Engines - Sources and Solutions. 28th CIMAC World Congr. 2016, Paper 032.
558 559
Control
Congr. 2010, Paper 106.
556 557
Emiss.
(39)
Lehtoranta, K.; Turunen, R.; Vesala, H.; Nyyssoenen, S.; Soikkeli, N.; Esselstroem, L. Testing SCR in High Sulphur Application. 27th CIMAC World Congr. 2013, Paper 107.
561
ACS Paragon Plus Environment
28