Characteristics of Particulate Matter Emissions from a Low-Speed

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Characteristics of Particulate Matter Emissions from a Low-Speed Marine Diesel Engine at Various Loads Hao Jiang, Gang Wu, Tie Li, Pengfei He, and Run Chen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b02341 • Publication Date (Web): 29 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019

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Environmental Science & Technology

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Characteristics of Particulate Matter Emissions from a Low-Speed Marine Diesel Engine at Various Loads

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Hao Jiang1, Gang Wu2, 3, Tie Li1, 2*, Pengfei He1, Run Chen4*

3

1

State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2

4

Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration,

5 6 7

Shanghai Jiao Tong University, Shanghai 200240, China 3

Merchant Marine College, Shanghai Maritime University, Shanghai 201306, China

4 Department

of Mechanical Engineering, Chiba University, Chiba 263-8522, Japan

8 9

ABSTRACT: Particulate matter (PM) emissions from ships are increasingly exposing the health risks for

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population living along coastal areas. However, studies on the characteristics of particulate emissions from ships

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fueled with heavy fuel oil (HFO) are quite rare yet. In this paper, the characteristics of PM sampled from the exhaust

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of a low-speed two-stroke common-rail marine diesel engine fueled with HFO are investigated at different loads. The

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thermal/optical carbon analyzer was employed to discriminate the elemental and organic carbons (EC and OC), the

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combustion-based elemental analysis was performed to obtain the C/H ratio, and the nuclear magnetic resonance

15

spectrometer was used to analyze the molecular structure in the sample. Increasing loads, the EC/OC and C/H mass

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ratios, and the mole ratio of polycyclic aromatic hydrocarbons (PAHs) to aliphatic hydrocarbons increase. From

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transmission electron microscopy (TEM) images, noticeable changes of soot particles in nanostructure, size,

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morphology and nanostructural parameters were analyzed. Furthermore, the elemental spatial distribution in soot

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particles was observed by the energy dispersive X-ray spectroscopy (EDS) mapping. The main elements were detected

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by the point- analyzed spectra. These results are believed to be valuable references for hazard evaluation and building

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strategy of reducing particulate emissions from low-speed marine diesel engines.

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ACS Paragon Plus Environment


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23 TOC Art

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INTRODUCTION Exhaust from marine diesel engines carries particulate matter that gives rise to increasing concern about potential

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effects on global climate change,1-4 air quality in coastal areas5,

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and ecosystem development.7 The need for

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international agreement on regulations of ship emissions, such as particulate matters (PMs), sulfur oxides (SOx),

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nitrogen oxides (NOx), is recognized,8 and it is to be expected that shipping and maritime industries face the much

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stricter legislation with respect to PMs in the future. Resulting from the fuel chemical composition and combustion

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conditions, PMs emitted from diesel engines are composed of soot and other components, for example, different salts,

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metals, and condensable matter. The large surface area of particles and the presence of metals and organics in particles

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all have increased the potential to produce oxidative stress.9 Soot particles can also cause health issues due to

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potentials of the mutagenic and carcinogenic effects.10

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In the last two decades, the seaborne trade has flourished in the world, especially in Asia.11 The world’s fleet

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includes approximately 55% low-speed engine, 40% medium speed engine and 5% other engine types.12 The most of

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heavy fuel oil and residual oil are used by the low-speed engines as the propulsion engines of merchant vessels. The

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combustion of cheap fuel oil has also caused serious environmental pollution. In recent years, lots of studies have

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been conducted on PM emissions from high speed and medium speed diesel engines. Although PMs emitted from

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low-speed two-stroke diesel marine engines fueled with HFO has greater oxidative stress and cytotoxicity, studies on

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the PM emissions are very limited yet.9, 13-20 The successful practice and experience in PM controls of high speed and 2


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medium speed diesel engines may be a valuable reference for low-speed marine engines. However, significant

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differences exist in operating modes, lubrication systems, and fuels etc. among these diesel engines. Although a lot

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of remarkable work has been achieved by some researchers,16-19 researches with respect to low-speed marine engines

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are far from adequate, even scarce yet.19

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Maintaining some form of ship speed (load) reductions is method for energy conservation and emission reduction.

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While, this strategy increases soot emission.21 In order to reduce soot emission from low-speed marine engines, it is

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necessary to completely investigate the composition and physicochemical characteristics as well as morphology and

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nanostructure of soot particles formed at the light, medium, medium-high and high loads. Such knowledge is very

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critical for understanding the mechanism of particle formation and oxidation, developing more advanced combustion

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strategies and optimizing the aftertreatment devices. Therefore further insights and information regarding to PMs

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from low-speed marine engines at different loads would be a valuable reference for reducing its emission, especially

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at the low load. The comprehensive information about the characteristics of PM from a low-speed two-stroke

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common-rail marine diesel engine is investigated in this paper.

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EXPERIMENTAL SETUP AND PROCEDURES

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Experimental Setup and Fuel Properties. The investigation was carried out on a six-cylinder direct-

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injected diesel engine with a total displacement of 894 liter. The engine features the turbocharger, intake air-cooling,

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high-pressure common rail fuel injection, and exhaust gas recirculation (EGR). The specifications of the marine diesel

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engine is shown in Table 1.

60 61 62 63 64 3



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65 Table 1. Specifications of the marine diesel engine.

66 Item

Specification

Type

2-stroke, L-6 marine, water-cooled, directinjection 350×1550 3750 142 180 17 380 Turbocharged

Cylinder bore × stroke (mm) Rated power (kw) Rated speed (r/min) Maximum indicated pressure (bar) Compression ratio Nozzle opening pressure (bar) Air admitting 67

The engine was operated at 25%, 50%, 75% and 90% loads, while the relation between speed and torque was

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controlled by considering the propeller characteristics. At start-up, the low-speed marine diesel engine operated about

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45 minutes to stabilize the coolant and lubricant temperatures before the measurements were implemented. HFO was

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used in this study. HFO is not a distilled fuel and the waste product from refinery processes. It typically contains

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components, such as asphaltenes, ash , and other sediments. It is necessary to filter and heat the HFO to 140–150℃

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before injection. Table S1 shows the fuel properties of HFO. The sulfur content is relatively low, but it is still very

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high compared to high-speed diesel engine fuels in China market, in which the sulfur content is usually no more than

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0.005%. 5040 of Sinopec lubricant, especially designed for the cylinder lubrication of low-speed two-stroke marine

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engine fueled HFO with sulfur content less than 2.5%, was used in the experiment.

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Filter sampling. The collection of particulate samples was performed in exhaust gas flow using a filter. The

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glass microfiber filter (Whatman Φ118.0 mm) fitted to a manifold of tailpipe of the engine and the distance between

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engine and sampling location is 12.5 m, running on the engine test bench on the steady state operation point (i.e. 25%,

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50%, 75% and 90% loads).The temperature of sampling location in the manifold was around 45 °C.

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Thermophoresis sampling. A novel thermophoresis sampling probe was used in the experiment.20, 22 In

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order to avoid disturbing the exhaust flow, the probe with a 3-mm TEM grid was placed in a direction approximately 4


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parallel to the axis of exhaust flow and used to sample PMs after the engine reached steady state. After each sampling,

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the grid was carefully moved from the probe to a special protective box and ready for the TEM observation.

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Characterization methods. The mass flow of exhaust gas based on carbon balance method was calculated

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and the gaseous emissions components and their concentrations were monitored by gas analyzer (PG-350, Japan

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Horiba).The DRI Model 2015 Thermal/Optical Carbon Analyzer (Atmoslytic Inc., Calabasas, CA, USA), following

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the IMPROVE TOR (thermal optical reflection) protocol, was used to analyze OC and EC in PMs samples. With this

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method, the oven temperature was stepwise heated from 50 ℃ to 580 ℃ within the helium environment, which

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determinate the thermo carbon fractions of OC1, OC2, OC3, and OC4. Then, a mixture of 2% oxygen and 98% helium

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was introduced into the system, and the oven was further stepped heated to 950 ℃ for determination of EC1, EC2

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and EC3 contents.23, 24 OC was calculated as OC1 + OC2+ OC3 + OC4 + OP, and EC contained EC1-OP, EC2, and

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EC3. OP was pyrolysis products of organic carbon and measured when reflected laser light attained its original

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intensity after oxygen was added to the system. The content of ash was acquired from the gravimetric difference

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between a 0.8 cm2 punch cut out from a glass microfiber filter before sampling and the same punch with PMs after

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the thermal program.

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Organic compounds adhering to the surface of PM was routinely extracted and replaced with deuterated

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chloroform and concentrated. All nuclear magnetic resonance (NMR) measurements were performed on a Bruker 600

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Ultrashield magnet with an AVANCE III 600 Console (Bruker Biospin, Billerica, MA) at 298 K. Elemental analysis

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of PM was carried out by the combustion method using a Vario EL Cube elemental analyzer. Carbon, hydrogen and

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oxygen were measured directly. The above experiments were repeated three times with good repeatability.

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The morphology and nanostructural parameters of soot particles were extracted and analyzed from (HR)TEM

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images by an in-house Matlab-based code.20, 22 Meanwhile, chemical composition distribution was determined by the

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HRTEM attached with an energy dispersive X-ray spectroscope (EDS) operating at an accelerating voltage of 200 kV.

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Finally, chemical composition spatial distribution of soot particles and element content of inner core were obtained 5



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by the EDS elemental mapping and EDS spectra.

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RESULTS AND DISCUSSION

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Contents of OC, EC and ash in PMs. As shown in Figure 1a, the trends of concentrations of THC and CO

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decrease firstly and then increase. Due to the local fuel-poor regions and the low temperature at the low load and the

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local fuel-rich regions at the high load, THC and CO are derived from HFO that is not fully combusted. So there are

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much more THC and CO at the low load and the high load. The incompletely burned HFO occupies a large mass

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fraction of exhaust emitted from the low-speed marine engine at the low load and the high load. This trend is consistent

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with the findings of Huang et al.25 Compared to THC and CO, the concentration of SO2 has the opposite tendency,

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which is attributable mainly to the lower oxygen concentration found at the high load.26 As the load increases, the

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temperature in the cylinder increases, resulting in more NOx emission at the higher load. The experiments were

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respectively carried out on marine engines by Choi et al.27 and Wu et al.26 , they all got the similar conclusions.

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The mass fractions of OC (OC1–OC4), EC (EC1–EC3) and ash at different loads are presented in Figure 1b.

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OC1–OC4 are respectively volatile, semi-volatile, non-volatile and tar-like organic compounds in PM samples. Their

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molecular weights are increasing.28, 29 At the low load, the mass fraction of OC emission is higher than that at the high

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load. OC is mainly formed from incomplete combustion fuel and lubricant. In the very short time, soot particles and

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a large amount of small molecule precursor of soot rapidly form in cylinders. At the low load, the lower combustion

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temperature inhibits fuel and lubricant pyrolysis and many tar-like soot particles are immature, so there are higher

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mass fractions of OC3 and OC4.The increase in mass fractions of OC1 and OC2 at the high load is mainly due to

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small molecule precursor adsorbing on the surface of already formed soot particles.27, 30 The EC composition is usually

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divided into two categories. EC1 is defined as char-EC and directly formed via the fuel pyrolysis at relatively low

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temperature ambient, while EC2 + EC3 is defined as soot-EC and derived from gas-to-particle conversion at high

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temperature ambient.31, 32 Therefore, the higher fuel injection mass and more local fuel-rich regions, as well as the

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higher temperature ambient at the high load could produce more EC. It can be found that the proportion of soot-EC 6


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increases faster. It also indicates that much more soot-EC is generated at the high load and higher temperature ambient.

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In the present study, the mass fraction of EC is about 7%-12%. It’s similar to the EC content in PMs from other marine

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engines and usually less than 10%.33, 34 While it generally contributes much more than 40% to total mass of PM

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emitted from the high-speed diesel engine,23, 24, 35 and is still higher than that from the medium speed diesel engine.13,

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36

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from the low load to the high load, the mass fractions of ash increase slightly. In addition, PMs formed at various

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loads causes different effects on human health. At the low load, PMs with higher proportions of organic carbon content

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causes greater responses in heart rate and T-wave morphology, in terms of both magnitude and rapidity of onset of

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eﬀects. However, PMs generated at the high load causes more lung inﬂammation and greater susceptibility to viral

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infection.37

When the soot sample contains less OC, the density of PM is lower. Due to the OC content in soot samples declining

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139 140

Figure 1. (a) Concentrations of THC, SO2, CO and NOx in exhaust; (b) Mass fractions of carbonaceous 7



components and ash at different loads.

141 142

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H NMR analysis. 1H NMR analysis is a technique that is routinely used to measure the composition of organic

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matter, such as PAHs and aliphatic hydrocarbons, adhering to the surface of PM. 1H NMR spectra is used to classify

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hydrogen groups via yielding structural information, so different kinds of organic matters, such as aromatic,

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naphthenic, isoparaffinic and paraffinic, were distinguished from complex mixtures. The hydrogen groups classified

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by 1H NMR spectra can yield structural information that allows the characterization of complex mixtures containing

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hundreds of aromatic, naphthenic, paraffinic, olefinic, and isoparaffinic compounds.38, 39 In the exhaust, particle-phase

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PAHs is an important part of the total PAHs which has mutagenic and carcinogenic potential.40 Figure 2 shows the

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histograms of PAHs and aliphatic hydrocarbons as well as the trend of mole ratio of aliphatic hydrocarbons to PAHs

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at different loads. The histograms show that PAHs increases with an increase in operation load, while its content still

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makes little contribution to the total organics. In contrast, although the total amount of aliphatic hydrocarbons slightly

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reduces, it still dominates. This phenomenon is consistent with the finding from Wang that the large amount of

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aliphatics were observed in nascent soot formed.41 The observation is accompanied by a decrease of the mole ratio of

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aliphatic hydrocarbons to PAHs. This result is just contrary to the result acquired by Santamaria et al.,42 in which

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there is a large amount of PAHs in the soot samples. The main reasons for this difference are due to the different fuels

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and combustion environments. As mentioned by Wang et al.,43 there is a definite correlation between aliphatic C–H

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groups and apparent activation energy, which has significant effect on oxidation reactivity of soot particles. So, PMs

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with relatively larger amounts of aliphatic groups generated at the light load is much easier to be oxidized and removed

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by the aftertreatment device equipped with a diesel particulate filter (DPF) using burner regeneration with catalyst.

8


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Figure 2. Effects of operation loads on mole ratio of aliphatic hydrocarbons to PAHs and their contents.

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Elemental analysis. The contents of C, H, O in PM samples generated from the low-speed engine are shown

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in Figure 3. The carbon content in the present study increases from 86.75% to 94.82%, accompanied by a

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corresponding reduction in the hydrogen and oxygen contents, which change from 7.52% to 4.36% and 5.73% to

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0.82%, respectively. Soot formation is concisely described and obeys the so called hydrogen-abstraction-carbon-

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addition (HACA) mechanism.44 The third part of soot formation process is carbonization of soot particles to form

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mature carbonaceous soot particles.45 Carbonization involving polymerization, dehydrogenation, and bond

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formation/rearrangements that results in the conversion of condensed media into solid material of high carbon

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content.46 Soot maturity is represented by its mass ratio of carbon to hydrogen (C/H) and the completed degree of

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carbonization process is characterized by the decreasing condensed phase hydrogen mole fraction. A detailed analysis

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shows that C/H in the samples increase significantly with loads. Especially more than 50% load, the chemical

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composition of samples changes dramatically. The increase of C/H should imply a change of the internal electronic

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structure in terms of the increase of sp2/sp3 hybridization ratio that implies the increase of graphitic planar structures47

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and justifies the higher oxidation resistance of PM at the high load. It is expected as the C/H ratio increases the soot

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particles tend to be more stable, and thus less chemically reactive.48 Compared with the C/H mass ratios of soot

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samples sampled from high-speed diesel engines (C/H = 28.57)35, 49 and premixed flames (C/H = 39.6),50 the C/H

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mass ratio in the present study is less than 21.8 at the high load, which means there are many immature particles and 9



178

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a large amount of unburned hydrocarbons in the samples.

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Figure 3. Elemental analysis of the soot samples gathered at different loads.

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Morphology and nanostructural parameter analysis of soot particles. TEM images of soot primary

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particles with a magnification of × 1,050,000 at 25%, 50%, 75% and 90% loads are respectively shown in Figure 4.

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At 25% load, chaotically graphitic segments in the interior of primary particle is surrounded by the outer shell with

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randomly oriented shorter graphitic layers. At 50% load, the length of lattice fringes are increasingly longer and the

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internal structure of soot primary particle gradually becomes regular from the former chaotic structure. At 75% load,

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the soot primary particle presents the more matured structure and the core is surrounded by the longer and more

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ordered lattice fringes. At 90% load, the inner core composed by several fine particles of 3–5 nm in diameter and the

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graphitic crystallite outer shell are easier to identify, indicating an obvious well-matured soot primary particle. Many

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studies have demonstrated that the nanostructure of particles closely relate to its oxidation activity. Specifically, the

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chaos and amorphous internal structures of immature soot particles have much higher oxidative activity and lower

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activation energy than the matured soot particles with graphite structures.51, 52 So the DPF with deposited soot particles

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formed at low load is easier to regenerate at the relatively lower temperature.

10


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193 194

Figure 4. Nanostructure of the soot primary particles gathered at different loads.

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The diameter (dm) of soot primary particles in the present study was manually extracted by a pretty skilled operator

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and the details can be found in our previous papers.20, 22 Based on statistical view, the diameter distribution of soot

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primary particles is respectively acquired from more than 30 TEM images at different loads.20,

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confidence level, the error of dm is less than ±0.1 nm. The number of soot primary particles being counted and the

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statistical results are shown in Figure 5. The slope of the dashed line representing the average diameter of soot primary

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particles gradually decreases from the low load to the high load. This trend is mainly due to the fact that at the low

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load, there are a large number of immature soot particles with larger diameter in the lower temperature ambient. At

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the medium load, many immature soot particles are easy to be oxidized by oxidants in the relatively higher

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temperature ambient, so the diameter of soot primary particles quickly decreases. At the 90% load, a large number of

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rapidly oxidized soot primary particles have smaller size and even disappear completely in the high temperature

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ambient. Those eventually existing soot particles with matured structure are more difficult to be further oxidized into

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smaller size, so the diameter distributions of soot primary particles are getting narrower and narrower. The average

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diameter of soot primary particles in the present study is similar to that emitted from other marine engine,17 while it

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is larger than that generated from high-speed diesel engines (no more than 30 nm).53, 54 According to the results, it 11


22

At the 95%


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can be speculated that except the difference of fuels, the ambient temperature also has significant effect on soot

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particles size.

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Figure 5. Diameter distribution of primary particles at different loads. The error of dm with 95% confidence level is less than ±0.1 nm.

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The radius of gyration (Rm) is an important parameter that can be used to characterize the compact degree of soot

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aggregate. When the number of soot primary particles in a aggregate is fixed, the smaller Rm means the soot aggregate

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more compact.20 The number of soot aggregates being counted and their radius of gyration at different loads are

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shown in Figure 6. At the 95% confidence level, the error of Rm is less than ±1.5 nm. At 25% load, larger radius of

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gyration of soot aggregates always have stretch structure with several branches. The structure is hard to change at the

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relatively lower temperature ambient. At 50% load, the radius of gyration of soot aggregates and the diameter of more

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matured soot primary particles are smaller than that at 25% load. At 75% load, the disintegration of soot primary

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particles and weakening “bridges” or connections between partially coalesced soot primary particles lead to the

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breakup of larger soot aggregate at the relatively higher temperature ambient. At 90% load, more compacted soot

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aggregates with the smaller radius of gyration could be resulted from oxidation of branches and breakup of larger

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soot aggregates at the high temperature ambient.20 Because immature soot particles covered without or with very

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thinner graphitic layers are easy to be oxidized into relatively matured soot particles and the stretch branches are 12


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disintegrated, so, the average value of Rm of soot aggregates and the slope of the dashed line in Figure 6 decrease

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from the low load to the high load. The average value of Rm is very similar to the result of soot particles from a marine

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engine48 and these values of Rm are much larger than that in high-speed diesel engines.55, 56

229 230 231

Figure 6. Radius of gyration of soot aggregates at different loads. The error of Rm with 95% confidence level is less than ±1.5 nm.

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The soot nanostructure affects the oxidation reactivity of soot, and Alfe` et al.50 also putted forward the same

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point. The average length, tortuosity and separation of the lattice fringes are selected to better characterize the change

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of nanostructural parameters of soot primary particles from the low load to the high load and shown in Figure 7a, b

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and c, respectively. At the 95% confidence level, the error bars are also shown in Figure 7. The average length of

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lattice fringes increases, and the average tortuosity and separation of lattice fringes decrease with the load increasing,

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as expected. The graphite layer plane growth also characterizes the completed degree of carbonization process.46 In

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the graphite layers with planar dimensions, the reactivity of carbon atom at the edge-site positions is higher than that

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at the basal plane.9, 20, 24 Longer lattice fringes in matured soot primary particles imply larger planar dimensions and

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a greater proportion of carbon atoms at the basal plane positions. Due to the lower reactivity of matured soot particles

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at the high load, the further structural change of particles becomes difficult once graphitization has occurred,31 thus 13



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the slope of the average length and separation of the lattice fringes of primary particles from 75% load to 90% load

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are reduced, as shown in Figure 7a and c. Compared with the nanostructural parameters of soot primary particles in

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the high-speed diesel engine,53 the lattice fringe tortuosity and separation in the present study are much larger. It

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indicates that soot particles are relatively immature in the low-speed marine engine.

246 247 248

Figure 7. (a) Average lattice fringe length; (b) Average lattice fringe tortuosity; (c) Average lattice fringe separation at different loads. The error bars obtained with 95% confidence level.

249

STEM-EDS analysis and spatial distribution of elemental composition in soot particles. The

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high-angle annular dark-field (HAADF) STEM image in Figure 8A shows a clear contrast difference between the

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core and the shell in particles which indicates the presence of elements with higher atomic numbers in the inner cores.

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The fine cores of primary particles in Figure S1 are strongly different from the cores inside of the matured soot

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primary particles in our previous study20 which shows the inner-structure with randomly oriented short graphene

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segments. At the magnification up to ×1,500,000, the high-resolution TEM image shows the distinct lattice fringes of

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the fine cores,57 which is the obvious characteristic of metal. EDS elemental mapping is conducted to determine the

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composition and used to visually observe the elemental spatial distribution in soot particles. Except for carbon, the 14


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main elements of soot particles are shown in Figure 8B-F. Oxygen, sulfur, calcium, nickel and iron are found to

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concentrate in the particles. The fine cores inside of the primary particles are the enrichment area of these elements,

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probably existing in the form of calcium, nickel and iron sulfate. Figure S1 shows the obvious EDS spectrum of a

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core in soot particle. The point-analyzed spectra was detected in position “a” in the TEM image of Figure S1. The

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dominant C and O, clearly identifiable Ca, S, Ni and Fe can be detected. Furthermore, the EDS spectrum of the HFO

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soot particle also exhibits the weak Al, Mg and V peaks. From a comparison based on EDS analysis studied by

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Popovicheva et al.,58 it is inferred that the V and Cu peaks are much weaker, while there is a stronger intensity Ni

264

peak. More than 80% of the total soot aggregates contain at least one or several metal-containing primary particles.

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Under normal operating conditions, metals in the engine exhaust are mostly believed to originate from by-products

266

of engine wear that enter the combustion chamber via reverse blow-by of the piston rings14 and the consumption of

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metal contents in HFO33 and lubricant. The internal mixing of sulfuric acid, transition metals and organics in exhaust

268

particles of marine engines raises additional concerns for human health as increased particle acidity may enhance the

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bioavailability of surface-bound metals.33,

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formation process. The generated metallic nanoparticles in soot aggregates create a potential health concern.9, 60 HFO

271

with high sulfur content increases PM emission and also causes catalyst failure in the aftertreatment device. Due to a

272

significant amount of metal contained in soot particles emitted from marine engines, the metal content in HFO should

273

be taken seriously and strictly controlled by the governments and fuel suppliers in the future.

59

The metal in HFO will promote nucleation of particle in the soot

274 15



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Figure 8. Visualization of element composition in a part of a soot aggregate. The HAADF-STEM image is

276

presented along with the EDS elemental mapping for O, S, Ca, Ni and Fe.

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ASSOCIATED CONTENT

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Supporting Information

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One figure and one table.

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AUTHOR INFORMATION

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Corresponding Authors

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*Phone: +86-21-3420-8348; Fax: +86-21-3420-8348; E-mail: [email protected].

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*Phone: +86-21-3420-8348; Fax: +86-21-3420-8348; E-mail: [email protected].

284

ORCID

285

Hao Jiang: 0000-0002-8135-9845

286

Tie Li: 0000-0003-0752-1223

287

Run Chen: 0000-0002-6861-9542

288

Notes

289

The authors declare no competing financial interest.

290

ACKNOWLEDGMENTS

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The financial supports by the National Natural Science Foundation of China (51776125 & 91541104) are gratefully

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acknowledged. We acknowledge the support received from all students in our laboratory.

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REFERENCES

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(1) Eyring, V.; Isaksen, I. S.; Berntsen, T.; Collins, W. J.; Corbett, J. J.; Endresen, O.; Stevenson, D. S. Transport

295

impacts on atmosphere and climate: Shipping. Atmos. Environ. 2010, 44(37), 4735-4771.

296

(2) Lauer, A.; Eyring, V.; Hendricks, J.; Jöckel, P.; Lohmann, U. Global model simulations of the impact of ocean-

297

going ships on aerosols, clouds, and the radiation budget. Atmos. Chem. Phys. 2007, 7(19), 5061-5079. 16


Page 17 of 27


298

(3) Fuglestvedt, J.; Berntsen, T.; Myhre, G.; Rypdal, K.; Skeie, R. B. Climate forcing from the transport sectors. Proc

299

Natl Acad Sci. 2008, 105(2), 454-458.

300

(4) Capaldo, K.; Corbett, J. J.; Kasibhatla, P.; Fischbeck, P.; Pandis, S. N. Effects of ship emissions on sulphur cycling

301

and radiative climate forcing over the ocean. Nature. 1999, 400(6746), 743-746.

302

(5) Corbett, J. J.; Winebrake, J. J.; Green, E. H.; Kasibhatla, P.; Eyring, V.; Lauer, A. Mortality from ship emissions:

303

a global assessment. Environ. Sci. Technol. 2007, 41(24), 8512-8518.

304

(6) Agrawal, H.; Eden, R.; Zhang, X.; Fine, P. M.; Katzenstein, A.; Miller, J. W.; Cocker III, D. R. Primary particulate

305

matter from ocean-going engines in the Southern California Air Basin. Environ. Sci. Technol. 2009, 43(14), 5398-

306

5402.

307

(7) Devasthale, A.; Krüger, O.; Graßl, H. Impact of ship emissions on cloud properties over coastal areas. Geophys.

308

Res. Lett. 2006, 33(2), doi: 10.1029/2005GL024470.

309

(8) van Aardenne, J.; Colette, A.; Degraeuwe, B.; Hammingh, P.; De Vlieger, I. The impact of international shipping

310

on European air quality and climate forcing. European Environment Agency, Copenhagen. 2013, doi: 10.2800/75763.

311

(9) Donaldson, K.; Tran, L.; Jimenez, L. A.; Duffin, R.; Newby, D. E.; Mills, N.; Stone, V. Combustion-derived

312

nanoparticles: a review of their toxicology following inhalation exposure. Part. Fibre Toxicol. 2005, 2(1), doi:

313

10.1186/1743-8977-2-10.

314

(10) Richter, H.; Howard, J. B. Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review

315

of chemical reaction pathways. Prog. Energ. Combust. 2000, 26(4-6), 565-608.

316

(11) Lv, Z.; Liu, H.; Ying, Q., Fu, M.; Meng Z.; Wang, Y.; Wei, W.; Gong, H.; He, K. Impacts of shipping emissions

317

on PM2: 5 pollution in China. Atmos. Chem. Phys. 2018, 18(21), 15811-15824.

318

(12) Kesgin, U.; Vardar, N. A study on exhaust gas emissions from ships in Turkish Straits. Atmos. Environ. 2001,

319

35(10), 1863-1870.

320

(13) Wu, D.; Li, Q.; Ding, X.; Sun, J.; Li, D.; Fu, H.; Teich, M.; Ye, X.; Chen, J. Primary particulate matter emitted 17



Page 18 of 27

321

from heavy fuel and diesel oil combustion in a typical container ship: characteristics and toxicity. Environ. Sci.

322

Technol. 2018, 52(21), 12943-12951.

323

(14) Sarvi, A.; Lyyränen, J.; Jokiniemi, J.; Zevenhoven, R. Particulate emissions from large-scale medium-speed

324

diesel engines: 1. Particle size distribution. Fuel Process. Technol. 2011, 92(10), 1855-1861.

325

(15) Sarvi, A.; Fogelholm, C. J.; Zevenhoven, R. Emissions from large-scale medium-speed diesel engines: 2.

326

Influence of fuel type and operating mode. Fuel Process. Technol. 2008, 89(5), 520-527.

327

(16) Kasper, A.; Aufdenblatten, S.; Forss, A.; Mohr, M.; Burtscher, H. Particulate emissions from a low-speed marine

328

diesel engine. Aerosol Sci. Technol. 2007, 41(1), 24-32.

329

(17) Lieke, K. I.; Rosenørn, T.; Pedersen, J.; Larsson, D.; Kling, J.; Fuglsang, K.; Bilde, M. Micro-and nanostructural

330

characteristics of particles before and after an exhaust gas recirculation system scrubber. Aerosol Sci. Technol. 2013,

331

47(9), 1038-1046.

332

(18) Sippula, O.; Stengel, B.; Sklorz, M.; Streibel, T.; Rabe, R.; Orasche, J.; Groger, T. Particle emissions from a

333

marine engine: chemical composition and aromatic emission profiles under various operating conditions. Environ.

334

Sci. Technol. 2014, 48(19), 11721-11729.

335

(19) Lee, W. J.; Park, S. H.; Jang, S. H.; Kim, H.; Choi, S. K.; Cho, K. H.; Choi, J. H. Carbon nanostructure of diesel

336

soot particles emitted from 2 and 4 stroke marine engines burning different fuels. J. Nanosci. Nanotechno. 2018, 18(3),

337

2128-2131.

338

(20) Jiang, H.; Li, T.; Wang, Y.; He, P.; Wang, B. The evolution of soot morphology and nanostructure along axial

339

direction in diesel spray jet flames. Combust. Flame. 2019, 199, 204-212.

340

(21) Lack, D. A.; Corbett, J. J.; Black carbon from ships: a review of the effects of ship speed, fuel quality and exhaust

341

gas scrubbing. Atmos. Chem. Phys. 2012, 12(9), 3985-4000.

342

(22) Jiang, H.; Li, T.; Wang, Y.; He, P. Morphology and nano-structure analysis of soot particles sampled from high

343

pressure diesel jet flames under diesel-like conditions. Meas. Sci. Technol. 2018, 29(4), doi: 10.1088/136118


Page 19 of 27


344

6501/aaa667.

345

(23) Li, X.; Xu, Z.; Guan, C.; Huang, Z. Particle size distributions and OC, EC emissions from a diesel engine with

346

the application of in-cylinder emission control strategies. Fuel. 2014, 121, 20-26.

347

(24) Lu, T.; Huang, Z.; Cheung, C. S.; Ma, J. Size distribution of EC, OC and particle-phase PAHs emissions from a

348

diesel engine fueled with three fuels. Sci. Total Environ.2012, 438, 33-41.

349

(25) Huang, C.; Hu, Q.; Li, Y.; Tian, J.; Ma, Y.; Zhao, Y.; Feng, J.; An, J.; Qiao L.; Wang, H.; Jiang, S.; Huang, D.;

350

Lou, S.; Zhou, M.; Zhu, S.; Tao, S.; Li, L. Intermediate volatility organic compound emissions from a large cargo

351

vessel operated under real-world conditions. Environ. Sci. Technol. 2018, 52(21), 12934-12942.

352

(26) Wu, D.; Ding, X.; Li, Q., Sun, J.; Huang, C.; Yao, L.; Wang, X.; Ye, X.; Chen, Y.; He, H.; Chen, J. Pollutants

353

emitted from typical Chinese vessels: Potential contributions to ozone and secondary organic aerosols. J. Clean. Prod.

354

2019, doi: 10.1016/j.jclepro.2019.117862.

355

(27) Choi, J. H.; Cho, I.; Lee, J. S.; Park, S. K.; Lee, W. J.; Kim, H.; Chang, H., J.; Kim, J., y.; Jecong, S.; Park, S. H.

356

Characterization of carbonaceous particulate matter emitted from marine diesel engine. J. Mech. Sci. Technol. 2016,

357

30(5), 2011-2017.

358

(28) Duan, J.; Tan, J.; Wang, S.; Chai, F.; He, K.; Hao, J. Roadside, Urban, and Rural comparison of size distribution

359

characteristics of PAHs and carbonaceous components of Beijing, China. J. Atmos. Chem. 2012, 69(4), 337-349.

360

(29) Chow, J. C.; Watson, J. G.; Crow, D.; Lowenthal, D. H.; Merrifield, T. Comparison of IMPROVE and NIOSH

361

carbon measurements. Aerosol Sci. Technol. 2001, 34(1), 23-34.

362

(30) Li, X.; Xu, Z.; Guan, C.; Huang, Z. Impact of exhaust gas recirculation (EGR) on soot reactivity from a diesel

363

engine operating at high load. Appl. Therm. Eng. 2014, 68(1-2), 100-106.

364

(31) Watson, J. G.; Chow, J. C.; Lowenthal, D. H.; Pritchett, L. C.; Frazier, C. A.; Neuroth, G. R.; Robbins, R.

365

Differences in the carbon composition of source profiles for diesel-and gasoline-powered vehicles. Atmos. Environ.

366

1994, 28(15), 2493-2505. 19



Page 20 of 27

367

(32) Han, Y.; Cao, J.;Chow, J. C.; Watson, J. G.; An, Z.; Jin, Z.; Liu, S. Evaluation of the thermal/optical reflectance

368

method for discrimination between char-and soot-EC. Chemosphere. 2007, 69(4), 569-574.

369

(33) Moldanová, J.; Fridell, E.; Popovicheva, O.; Demirdjian, B.; Tishkova, V.; Faccinetto, A.; Focsa, C.

370

Characterisation of particulate matter and gaseous emissions from a large ship diesel engine. Atmos. Environ. 2009,

371

43(16), 2632-2641.

372

(34) Agrawal, H.; Malloy, Q. G. J.; Welch, W. A.; Miller, J. W.; Cocker III, D. R. In-use gaseous and particulate matter

373

emissions from a modern ocean going container vessel. Atmos. Environ. 2008, 42(21), 5504-5510.

374

(35) Clague, A. D. H.; Donnet, J. B.; Wang, T. K.; Peng, J. C. M. A comparison of diesel engine soot with carbon

375

black. Carbon. 1999, 37(10), 1553-1565.

376

(36) Zhang, F.; Chen, Y.; Tian, C., Luo, D.; Li, J.; Zhang, G.; Matthias, V. Emission factors for gaseous and particulate

377

pollutants from offshore diesel engine vessels in China. Atmos. Chem. Phys. 2016, 16(10), 6319-6334.

378

(37) McDonald, J. D.; Campen, M. J.; Harrod, K. S.; Seagrave, J.; Seilkop, S. K.; Mauderly, J. L. Engine-operating

379

load influences diesel exhaust composition and cardiopulmonary and immune responses. Environ. Health Persp. 2011,

380

119(8), 1136-1141.

381

(38) Guillén, M. D.; Dı́az, C.; Blanco, C. G. Characterization of coal tar pitches with different softening points by 1H

382

NMR: role of the different kinds of protons in the thermal process. Fuel Process. Technol. 1998, 58(1), 1-15.

383

(39) Lee, S. W.; Glavincevski, B. NMR method for determination of aromatics in middle distillate oils. Fuel Process.

384

Technol. 1999, 60(1), 81-86.

385

(40) He, C.; Ge, Y.; Tan, J.; You, K.; Han, X.; Wang, J. Characteristics of polycyclic aromatic hydrocarbons emissions

386

of diesel engine fueled with biodiesel and diesel. Fuel. 2010, 89(8), 2040-2046.

387

(41) Wang, H. Formation of nascent soot and other condensed-phase materials in flames. P. Combust. Inst. 2011,

388

33(1), 41-67.

389

(42) Santamaria, A.; Yang, N.; Eddings, E.; Mondragon, F. Chemical and morphological characterization of soot and 20


Page 21 of 27


390

soot precursors generated in an inverse diffusion flame with aromatic and aliphatic fuels. Combust. Flame. 2010,

391

157(1), 33-42.

392

(43) Wang, L.; Song, C.; Song, J.; Lv, G.; Pang, H.; Zhang, W. Aliphatic C–H and oxygenated surface functional

393

groups of diesel in-cylinder soot: Characterizations and impact on soot oxidation behavior. P. Combust. Inst. 2013,

394

34(2), 3099-3106.

395

(44) Frenklach, M. Reaction mechanism of soot formation in flames. Phys. Chem. Chem. Phys. 2002, 4(11), 2028-

396

2037.

397

(45) Reilly, P. T. A.; Gieray, R. A.; Whitten, W. B.; Ramsey, J. M. Direct observation of the evolution of the soot

398

carbonization process in an acetylene diffusion flame via real-time aerosol mass spectrometry. Combust. Flame. 2000,

399

122(1-2), 90-104.

400

(46) Vander Wal, R. L. Soot precursor carbonization: Visualization using LIF and LII and comparison using bright

401

and dark field TEM. Combust. Flame. 1998, 112(4), 607-616.

402

(47) Tregrossi, A.; Barbella, R.; CIAJOLO*, A.; Alfè, M. Spectral properties of soot in the UV-visible range. Combust.

403

Sci. Technol. 2007, 179(1-2), 371-385.

404

(48) Kholghy, M. R.; Veshkini, A.; Thomson, M. J. The core–shell internal nanostructure of soot–A criterion to model

405

soot maturity. Carbon. 2016, 100, 508-536.

406

(49) Yehliu, K.; Vander Wal, R. L.; Armas, O.; Boehman, A. L. Impact of fuel formulation on the nanostructure and

407

reactivity of diesel soot. Combust. Flame. 2012, 159(12), 3597-3606.

408

(50) Alfè, M.; Apicella, B.; Rouzaud, J. N.; Tregrossi, A.; Ciajolo, A. The effect of temperature on soot properties in

409

premixed methane flames. Combust. Flame. 2010, 157(10), 1959-1965.

410

(51) Musculus, M. P.; Miles, P. C.; Pickett, L. M. Conceptual models for partially premixed low-temperature diesel

411

combustion. Prog. Energ. Combust. 2013, 39(2-3), 246-283.

412

(52) Su, D. S.; Jentoft, R. E.; Müller, J. O.; Rothe, D.; Jacob, E.; Simpson, C. D.; Niessner, R. Microstructure and 21



Page 22 of 27

413

oxidation behaviour of Euro IV diesel engine soot: a comparative study with synthetic model soot substances. Catal.

414

Today. 2004, 90(1-2), 127-132.

415

(53) Lu, T.; Cheung, C. S.; Huang, Z. Effects of engine operating conditions on the size and nanostructure of diesel

416

particles. J. Aerosol Sci. 2012, 47, 27-38.

417

(54) Wentzel, M.; Gorzawski, H.; Naumann, K. H.; Saathoff, H.; Weinbruch, S. Transmission electron microscopical

418

and aerosol dynamical characterization of soot aerosols. J. Aerosol Sci. 2003, 34(10), 1347-1370.

419

(55) Zhu, J.; Lee, K. O.; Yozgatligil, A.; Choi, M. Y. Effects of engine operating conditions on morphology,

420

microstructure, and fractal geometry of light-duty diesel engine particulates. P. Combust. Inst. 2005, 30(2), 2781-

421

2789.

422

(56) Lee, K. O.; Cole, R., Sekar, R.; Choi, M. Y.; Kang, J. S.; Bae, C. S.; Shin, H. D. Morphological investigation of

423

the microstructure, dimensions, and fractal geometry of diesel particulates. P. Combust. Inst. 2002, 29(1), 647-653.

424

(57) Chen, Y.; Shah, N.; Huggins, F. E.; Huffman, G. P. Investigation of the microcharacteristics of PM2. 5 in residual

425

oil fly ash by analytical transmission electron microscopy. Environ. Sci. Technol. 2004, 38(24), 6553-6560.

426

(58) Popovicheva, O.; Kireeva, E.; Shonija, N.; Zubareva, N.; Persiantseva, N.; Tishkova, V.; Mogilnikov, V. Ship

427

particulate pollutants: Characterization in terms of environmental implication. J. Environ. Monitor. 2009, 11(11),

428

2077-2086.

429

(59) Healy, R. M.; O'Connor, I. P.; Hellebust, S.; Allanic, A.; Sodeau, J. R; Wenger, J. C. Characterisation of single

430

particles from in-port ship emissions. Atmos. Environ. 2009, 43(40), 6408-6414.

431

(60) Miller, A.; Ahlstrand, G.; Kittelson, D.; Zachariah, M. The fate of metal (Fe) during diesel combustion:

432

Morphology, chemistry, and formation pathways of nanoparticles. Combust. Flame. 2007, 149(1-2), 129-143.

433

22


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Table 1. Specifications of the marine diesel engine.

1 Item

Specification

Type

2-stroke, L-6 marine, water-cooled, directinjection 350×1550 3750 142 180 17 380 Turbocharged

Cylinder bore × stroke (mm) Rated power (kw) Rated speed (r/min) Maximum indicated pressure (bar) Compression ratio Nozzle opening pressure (bar) Air admitting 2

3 4

5 6 7

Figure 1. (a) Concentrations of THC, SO2, CO and NOx in exhaust; (b) Mass fractions of carbonaceous components and ash at different loads. 1



8

9 10

Figure 2. Effects of operation loads on mole ratio of aliphatic hydrocarbons to PAHs and their contents.

11

12 13

Figure 3. Elemental analysis of the soot samples gathered at different loads.

14 15 16 17 18 19

2


Page 24 of 27

Page 25 of 27


20 21

Figure 4. Nanostructure of the soot primary particles gathered at different loads.

22

23 24 25

Figure 5. Diameter distribution of primary particles at different loads. The error of dm with 95% confidence level is below ±0.1 nm.

26

3



Page 26 of 27

27 28 29

Figure 6. Radius of gyration of soot aggregates at different loads. The error of Rm with 95% confidence level is below ±1.5 nm.

30

31 32 33

Figure 7. (a) Average lattice fringe length; (b) Average lattice fringe tortuosity; (c) Average lattice fringe separation at different loads. The error bars obtained with 95% confidence level.

34

4


Page 27 of 27


35 36

Figure 8. Visualization of element composition in a part of a soot aggregate. The HAADF-STEM image is

37

presented along with the EDS elemental mapping for O, S, Ca, Ni and Fe.

38

5


Characteristics of Particulate Matter Emissions from a Low-Speed

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