LNG vs. MDO in Marine Fuel Emissions Tracking

Abstract

The continuous increase in global maritime freight transport has led to an increase in emissions. The port of Heraklion was selected as a case study to investigate the environmental impact of shipping in wider areas. Two different maritime fuels were examined: the conventional maritime fuel, marine diesel oil (MDO), and an alternative maritime fuel, liquified natural gas (LNG). To carry out this study, real data from the port of Heraklion, the Lloyd’s Register Fairplay (LRF) Sea-Web database, and literature reviews were used. The bottom-up method was adopted for data processing. The results of this study demonstrate that alternative maritime fuels, such as LNG, could drastically reduce SO₂, NOx, PM, and CO₂ emissions.

1. Introduction

Global economic development is based on ship trade. For this reason, maritime emissions are considered a significant source of air pollution that has a negative impact on human health and the atmospheric environment. The global waterborne trade is expected to reach more than 15,000 million tons by 2035, with a slight increase over the long-term historical average [1,2]. Greenhouse gases (GHGs), ozone and aerosol precursors, sulfur oxides (SO_X), particulate matter (PM), nitrogen oxides (NO_X) [3,4,5,6], and volatile organic compounds (VOCs) are the main factors that contribute to air pollution and cause climate change [7,8,9]. The toxicity of these pollutants is dangerous for human health and the environment [10]. Fuels that are related to SO_X and NO_X emissions are the main cause of water and soil acidification since both are easily converted into active acid [11]. NO_X, SO_X, and PM emissions are also toxic to humans [4,12]. At least 70% of emissions from ships that operate on international routes occur within 400 km from the coast, according to recent studies [13]. For these reasons, it is crucial to improve maritime legislation in order to reduce emissions and their effect on nature [2,14,15].

At a global level, total GHG emissions from the shipping industry increased by 9.6% between 2012 (977 Mt) and 2018 (1076 Mt4), according to the IMO’s fourth GHG study [16]. As a result, the share of global anthropogenic emissions attributed to shipping increased from 2.76% in 2012 to 2.89% in 2018. During the same period, CO₂ emissions increased by 9.3%, from 962 Mt to 1056 Mt. International ships, on the other hand, contribute 2% of global GHG emissions and, based on the new voyage-based allocation, CO₂ emissions increased by 5.6%Mt in 2018, from 701 Mt in 2012 to 740. Furthermore, total shipping (international and domestic) emissions are expected to rise from around 1000 Mt CO₂ in 2018 to 1000–1500 Mt CO₂ by 2050, representing a 0–50% increase from 2018 levels and a 90–130% increase from 2008 levels.

Shipping emissions that are related to the potential growth of the economy and changes in the energy sector could rise by 50 to 250% by 2050 [17].

Moreover, emissions are expected to rise from roughly 90% of 2008 levels in 2018 to 90–130 percent of 2008 levels by 2050 under a variety of plausible long-term economic and energy-related scenarios. Although it is too soon to assess the quantitative impact of COVID-19 on emission projections, it is clear that emissions in 2020 and 2021 were significantly lower. Depending on the rate of recovery, emissions in the coming decades may be a few percentage points lower than predicted. Overall, the impact of COVID-19 is likely to be reduced.

With regard to international regulations on emissions from shipping, there are several regulations and directives that have been formulated to reduce NO_X, SO_X, and CO₂ emissions. The most relevant convention is IMO’s MARPOL 73/78 Convention, which specifies air pollution limits in Annex VI entitled “Regulation on the Prevention of Air Pollution from Ships”. The European Union implemented the Directive 2012/33/EU, amending the Directive 1999/32/EC, which is related to the quantity of sulfur in shipping fuels and is compatible with IMO standards, but it does not include guidance as to how to control NO_X and PM emissions. Stricter sulfur limits for marine fuels in sulfur emission control areas (SECAs) and nitrogen oxide emission control areas (NECAs) are also included in this directive [18]. The Baltic Sea, the North Sea, the region of North America (including the coastal part of Canada and USA), and the areas of the Caribbean Sea that belong to the USA (around Puerto Rico and the United States Virgin Islands) are all known as SECAs [18,19]. To comply with the EU Directive 2005/33/EC, ships that are berthing or approaching European ports must use marine fuel oils that contain less than 0.1% sulfur by mass (1.00% by mass until 31 December 2014 and 0.10% by 1 January 2015). For non-SECAs (3.50 percent by mass from 18 June 2014), see Figure 1 [9,20,21].

However, it is important to remember that SO₂ emissions are a significant contaminant in ports [23]. As a result, from 1 January 2020, the sulfur limits on ship fuels were importantly reduced worldwide, according to the EU sulfur regulation document. For this reason, four realistic methods have been proposed for the reduction in sulfur emissions limits [24,25], which can be sorted in two categories depending on the need for ship modification.

Non-Modification Methods

The first category is the use of low-sulfur fuel oil (LSFO) with the dominant method being to simply switch to LSFO marine fuel since the existing infrastructure is functional without requiring any change. LSFO prices, on the other hand, are over 30% higher compared to heavy fuel oil (HFO) since there are not enough refineries to produce sufficient amounts of LSFO [26].

The next method is to replace HFO with marine gas oil (MGO). MGO can use also the existing systems, so no additional infrastructure is needed. On the other hand, its use can influence ship operations, such as engine maintenance, speed, and combustion characteristics [27].

Modification Methods

The third choice is the use of heavy fuel oil (HFO) with the addition of a scrubber to remove SO_X. The device specifications require a relatively large space within the ship for installation, making the procedure difficult on small vessels [28], and the final cost of modification is usually very expensive.

The fourth choice is to use liquefied natural gas (LNG) to replace HFO. LNG is a natural gas that is temporarily converted to liquid form at low temperatures to facilitate storage and transportation. There are some issues with LNG marine fuel, such as the large initial amount that needs to be invested in order to cope with the lack of infrastructure for supplying LNG services [29,30,31]. However, LNG complies with IMO environmental regulations because it can significantly minimize air emissions due to its lower peak temperatures during combustion [32,33]. In comparison to HFO, LNG shipping fuel can reduce NO_X emissions by 85–95%, CO₂ by 20%, and SO_X by 100% [34]. As a result, liquefied natural gas marine fuel is a good choice to reduce air pollution and has become a valid alternative to the conventional fuel oils that have traditionally been used for ship propulsion. The key justification for the use of natural gas as an alternative fuel is that global LNG output from gas wells is predicted to rapidly increase in the short term. By 2050, LNG could provide for 32% of shipping energy demands [24]. Furthermore, natural gas is much less expensive than fossil fuels. The cost of LNG is roughly 60% of the cost of HFO [35,36], although there have been intense fluctuations in recent years. In addition, LNG has benefited greatly from investments made through the NOx fund [36]. Importantly, Ushakov, Stenersen, and Einang [37] noted that “engines tend to be overtuned” and have exceptionally low NOx emissions as a result (lower than the limit set by the standards). LNG is gaining traction as a viable potential source of power.

On the other hand, regarding the impact of pollutant emissions in Greece at the local level, ships in Greek waters emit 7.4 million tons of CO₂, according to estimates (at least 7 million tons of CO₂). It should be noted that Greece contributed 7.3% and 14.1% of the census of shipping emissions in the same year [38].

This article aims to contribute toward filling the gaps in current literature regarding the differences in ship emissions between MDO and LNG maritime fuel use and to include an assessment of the emissions inventory by introducing a ship activity-based methodology using data collected from the port of Heraklion [39] and the Lloyd’s Register Fairplay (LRF) Sea-Web database [40]. A distance of 10 km from the Heraklion’s port region was studied to estimate the total cruising emissions from ships that berth in the port and ships that use routes within the wider area [10]. This examination was based on the use of different fuels in different types of vessels. In this paper, we examined the argument that the switch to LNG fuel should be universal, implying that all ships should henceforth run on LNG. The emissions from different case studies were compared. Heraklion is one of the most important ports in Greece and was selected as the case study. Heraklion is located on the north coast of Crete, about 145 km east of Chania, 80 km east of Rethymnon, and 3 km west of Nikos Kazantzakis International Airport (airport code HER). The port of Heraklion is also one of the busiest ports in Greece. It serves one of the five most populous islands in the Mediterranean and is also the main port of a spectacular and popular tourist destination. Approximately two million passengers visit each year. Crete is visited by a considerable number of ships of various uses and sizes.

Section 1 of this paper presents the literature analysis. Section 2 describes the methodology used to conduct the research. The results of case study analysis are shown in Section 3. The paper is summarized by conclusions and directions for future research, which are presented in Section 4.

2. Emissions Calculation Methodology

The atmospheric emission inventory guidebook contains detailed methods for preparing ship emission inventories. The two main strategies for creating ship pollution inventories are the top-down and bottom-up methods.

Top-down Approach: the top-down approach is based on fuel consumption reports and is typically used when there is no available information about the ship’s detailed activity and/or status during various operational phases.

Bottom-up method: the bottom-up approach, on the other hand, is employed when the data availability guarantees the detailed calculation of fuel consumption and air emissions during each operational phase (i.e., cruise, maneuvering, at berth) of the ship, thus providing the spatial allocation of the air emissions. The bottom-up method uses ship movements, characteristics, and emission variables to estimate the ship- and route-related emissions [13].

Heraklion is the Greek port case study, the location of which is shown in Figure 2a.

Heraklion’s main port is part of the region within which emissions are calculated. The cruising and maneuvering activity lines are shown in Figure 2b,c. The Heraklion Port Authority calculated the ship routes as the best routes for ships to take based on the sea depth.

Table 1. The distance required for each ship activity (km).

Symbol	Ship Activity	Distance (km)
A–B	CRUISING	10.0
B–C–D	MANEUVERING	1.7

shows the distances for each activity of a ship. “A” is the point at which each ship begins cruising into the Heraklion port using a pilot. It should be noted though that RoPax vessels do not require piloting services. “B” is the point at which the cruise comes to an end and the maneuver begins. “D” indicates Heraklion port’s field.

Following the objective of this study, the contaminants generated by the conventional MDO fuel were investigated since any ship entering the port is required by port regulations to change its fuel from HFO to MDO. The traffic statistics for the port under consideration are shown in

Table 2. The traffic statistics and fuel types.

		Conventional Fuel (MDO)	Alternative Fuel (LNG)		Ship Calls
		Diesel Engine	LPDF 4-Stroke	LPDF 2-Stroke
Ship Category	Cruise Ships	X	X		187
	RoPax	X	X		1404
	Container Ships	X		X	45
	Vehicle Carriers	X	X		10
	General Cargo	X		X	80

.

Table 2 displays the type of conventional fuel (MDO) consumed by each group of ships entering the port of Heraklion, as well as the type of alternative fuel (LNG) those ships are able to consume in the future to minimize emissions. RoPax is the most vessel category in Heraklion port, followed by the other categories, such as cruise ships, etc.

The propulsions of the main engine and the secondarily auxiliary engine that generate electricity for ship functions are the emission sources from operational ships. Vessels in the port area produce emissions from both the main and auxiliary engines during maneuvering for berth and anchor, while the auxiliary engines are the only source of emissions when the ship is either anchored or berthed. Ship activities can be divided into three categories: maneuvering, hoteling, and cruising. The energy consumption of ship must be calculated for each mode of operation. Fuel and engine type, operation mode, fuel consumption, time in operating mode, and pollution factors are all parameters that affect ship emissions [41]. Emissions in Heraklion port are defined for every mode of operation and refer exclusively to ships that have entered and left the port. For each ship call, the expression in Equation (1) [42,43] is used to estimate each of the air pollutants (CO₂, CO, NOx, SO₂, HC, CH₄, and PM) emitted for the ship’s operating time in the port.

$$E_{i,f}={{\displaystyle \sum }}_{j,k}(T_j\times P_k\times L{F}_{j,k}\times E{F}_{i,f}),$$

(1)

where E represents the total amount of ship emissions (tons); i denotes the emission type (SO₂, NO_X, CO, HC, CH₄ or PM2.5); j denotes the vessel’s operation phase (i.e., sailing, maneuvering or hoteling); f specifies the type of fuel (conventional (c) or alternative (a)); k denotes the type of the engine ((ME) for main and (AE) for auxiliary); and P denotes the power of the engine (kW). The amount of power used by the engine during a given operation is the engine load factor (LF). T is the time spent in each of the ship’s operation phases (hours). T_C = D/U stands for the average time spent cruising (hours), where D is the ship’s range or the distance traveled at sea within a range of 10 km from Heraklion’s coastline (km) [10,44]. The ship moving velocity is denoted by U and is the average speed of each category of ships entering the port of Heraklion in cruising mode. T_M stands for the average time spent maneuvering (hours) and T_H stands for the average time spent at berth (hours) [43]. A careful evaluation of the available routes and velocity patterns that ships follow in port was carried out in the current study and a generic cruise ship path was created through detailed personal communications with local port authorities, ship operators, and observations of the case study port. This path was used to calculate the moving and maneuvering times, while the hoteling times for all types of ship calls were extracted from the relevant detailed data provided by local port authorities for the period under consideration. The average load factors for the main and auxiliary engines for each mode of ship activity (cruising, maneuvering, and hoteling) in the Mediterranean port of Heraklion were calculated according to these data and are shown in

Table 3. The engine load factors for ship activities within the port of Heraklion.

Activity	Cruise Ships		Coastal Passenger Ships		Other Ships
	ME	AE	ME	AE	ME	AE
Cruising	0.80	0.75	0.80	0.75	0.80	0.75
Maneuvering	0.20	0.75	0.20	0.75	0.40	0.75
Hoteling	0.00	0.60	0.00	0.45	0.00	0.75

[45,46,47].

The emissions factor (g/kW h) was calculated using comprehensive vessel data, such as engine and fuel type (conventional and alternative fuels), but there could be some uncertainties [7,48]. All required data concerning ship activities in Heraklion port in 2018, such as maneuvering and hoteling periods, ship calls, names of vessels, dates, and duration of calls (time between arrival and departure), and ship speed, are meticulously gathered by local port authorities. The average installed main engine (ME) power (per ship, engine type, and size class), as well as the distribution of two-stroke and four-stroke engines, were derived from the Lloyd’s Register Fairplay (LRF) Sea-Web database [40]. Recent research [49,50] was adopted to calculate the power of the auxiliary engines (AE) of cruise ships using the IMO energy efficiency design index [51], while the power of the AEs of the other categories of ships was taken from

Table 4. Maximum continuous rating.

MCRME	>10,000 KW	<10,000 KW
PowerAE	(0.025 × MCRME) + 250	0.05 × MCRME

[10,44].

Cruise ships, RoPax (roll-on/roll-off passenger) ships, vehicle ships, and general cargo ships are the specific types of ships that were under investigation in Heraklion port.

3. Results and Discussion

The results of the activity-based emissions model were used to measure maritime emissions in this analysis.

Table 5. The estimated amounts of emissions (tons/year) by pollutant category and fuel type.

	Emissions (tons/year)
	Conventional Fuels (MDO)	Alternative Fuels (LNG)	Difference (tons/year)	Percentage of Change
CO2	35,564.2	28,202.53	7361.67	20.70%
NOx	893.13	145.94	747.19	83.66%
CO	31.97	87.12	−55.15	Increase in emissions
HC	0.69	9.56	−8.87	Increase in emissions
PM	10.24	0.19	10.05	98.14%
SO2	36.28	0.19	36.09	99.48%
CH4	0.69	332.71	−332.02	Increase in emissions
Total	36,537.2	28,778.24	7758.96	21.24%

shows the calculated sum of shipping pollution in 2018. The sum of NOx emissions from all ships approaching Heraklion port that were burning conventional fuels was 893.13 t (2.44% of the total), the sum of SO₂ emissions was 36.28 t (0.10% of the total), the sum of CO₂ emissions was 35,564.20 t (97.34% of the total), the sum of PM emissions was 10.24 t (0.03% of total), the sum of HC and CH₄ emissions was 0.69 t (0% of the total), and the sum of CO emissions was 31.97 t (0.09% of the total). The total NO_X emissions from ships using alternative fuels, such as LNG, were 145.94 t (0.51% of the total), the total SO₂ emissions as well as the total PM emissions were 0.19 t (0% of the total), the total CO₂ emissions were 28,202.53 t (98% of the total), the total HC emissions were 9.56 t (0.03% of the total), the total CO emissions were 87.12 t (0.30% of the total), and the total CH₄ emissions were 332.71 t (1.16% of the total). As also shown in Table 5, the percentage reduction in sulfur dioxide and particulate matter emissions was almost 100% for LNG compared to MDO. The percentage reduction in NOx and CO₂ emissions was 83.66% and 20.70% respectively. However, there were increased emissions for the CO, HC, and CH₄ pollutants, which means that there is an adverse effect of switching from conventional fuel to alternative fuel for these specific pollutants. This is caused due to the “methane slip”, which occurs when unburned methane from the fuel is released in combination with the exhaust gas [31].

Figure 3 shows the port’s environmental profit per ship category, as well as the percentage of pollution reduction based on the different types of ships. Cruise ships were the dominant category of ships in terms of environmental profit due to their large technical characteristics, such as the power of the main engine, the power of the auxiliary engine, etc.

Figure 4 shows that RoPax ships accounted for the vast majority of vessel emissions (84.47% of the total emissions) in the examined port, followed by cruise ships (11.41% of the total emissions), regardless of the type of fuel used. Since the port of Heraklion is a very popular tourist destination, the RoPax and cruise ship categories account for the majority of pollution. When it comes to conventional fuels, CO₂ was the most prevalent pollutant, followed by NOx emissions, with SO₂ being the third ranked pollutant. Owing to the longer distances, emissions during cruising were higher than the emissions during maneuvering and hoteling when the ME and AE were both operating at full load.

Figure 5 depicts the emissions of a ship during each of the hoteling, maneuvering, and cruising modes. Ship emissions of exhaust gas contaminants during cruising accounted for 49.7% of overall emissions in operating modes. Furthermore, for ships using conventional fuels, emissions were 10.59% during maneuvering and 39.72% during hoteling. When the ME and AE used LNG as fuel, the above percentages adjusted to 46.65% in cruising mode, 11.25% in maneuvering mode, and 42.24% in hoteling mode.

The above results can be compared to existing research findings for different dates and different ports, as shown in

Table A3. Ship emissions in other ports.

Region/Ports	Air Pollutant Emissions (10 thousand tons/year)							Year	Reference
	SOx	NOx	CO	HC	PM2.5	PM10	CO2
Greece/Piraeus, Santorini, Mykonos, Corfu and Katakolo Ports	0.07 a	0.18	-	ND b	0.009	-	-	2013	[41,42]
Greece/18-ports	0.09 a	0.24	-	ND b	-	0.001	-	2013	[50]
Portugal/4-Ports	1.37 a	2.95	-	0.12	-	0.15	-	2014	[10]
Spain/Las Palmas Port	0.14 a	0.42	-	ND b	-	0.03	-	2011	[55]
India/JN-New Bombay Port	0.03 a	0.03	-	ND b	-	0.003	-	2006	[55]
China/Shanghai Yangshan Port	0.56 a	1.07	-	0.05	-	0.08	-	2009	[56]
China/Tianjin Port	2.93 a	4.13	-	0.17	-	0.4	-	2014	[57]
Korea/Busan Port	0.82 a	0.87	-	0.06	-	ND b	-	2009	[58]
Taiwan/Kaohsiung, Keelung, and Taichung Ports	0.11 a	0.11	-	0.003	-	0.009	-	2012	[49]
Turkey/İzmit Gulf	0.43 a	0.53	-	0.02	-	0.05	-	2005	[59]
Turkey/Ambarlı Port	0.02 a	0.08	-	ND b	-	0.003	-	2009	[41]
Turkey/İzmir Port	0.14 a	0.19	-	0.016	-	0.013	-	2007	[44]
Turkey/Çandarlı Port	0.06 a	0.06	-	0.005	-	0.003	-	2007	[60]
Hong Kong Port	1.24	1.45	0.14	/	/	0.14	-	2007	[61,62]
Shenzhen Port	1.36	2.33	0.22	/	0.17	0.22	-	2010	[63]
Shanghai Port	5.12	5.82	-	0.46	/	/	-	2003	[64]
Shanghai Port	3.54	5.73	0.49	0.21	0.37	0.46	-	2010	[65]
Shanghai Port	8.16	15.18	0.71	/	1.14	1.23	-	2010	[66]
Yangshan	0.56	1.08	0.11	0.05	0.09	0.11	-	2009	[56]
YRD port	38	71	2.9	/	5.1	5.7	-	2010	[66]
Tianjin Port	2.93	4.13	0.36	0.17	0.37	0.4	-	2014	[57]
Tangshan Port	7.97	11.22	0.87	0.36	0.70	0.76	-	2014	[6]
Qinhuangdao Port	6.44	8.63	0.67	0.28	0.55	0.60	-	2014	[67]
Huanghua Port	2.63	3.46	0.27	0.11	0.23	0.25	-	2014	[67]
Bohai Gulf	23.09	30.58	4.79	0.99	1.97	2.15	-	2014	[67]
Bohai Gulf	12.07	17.38	1.44	0.61	/	1.53	-	2014	[67]
National inland river	/	81	17	4.3	/	3.6	-	2010	[6]
Turkey/Ambarlı Port	0.0242	0.0845	0.2127	-	-	0.0036 c	7.859	2009	[41]
Turkey/İzmir Port	0.1405	0.1923	-	0.0074	-	0.0165 c	8.2753	2013	[44]

^a Emissions of SO₂; ^b ND, not determined; ^c any type of PM emissions.

(see Appendix A). The studies included in Table A3 clearly show the contribution of LNG fuel to the environmental profit of a port, as do our results, because the conversion of conventional fuel into LNG results in a significant reduction in emissions.

4. Conclusions

Annual SO₂, CO₂, CO, NOx, HC, CH₄, and PM emissions from five distinct kinds of ships in Heraklion port were estimated for 2018. The emissions were calculated depending on the ship category, operation mode, and fuel type. In 2018, NOx emissions totaled 893.13 tons, SO₂ emissions totaled 36.28 tons, CO₂ emissions were 35,564.2 tons, CO emissions totaled 31.97 tons, PM emissions totaled 10.24 tons, and HC and CH₄ emissions totaled 0.69 tons. The environmental profit of the port with the change of ship fuel from MDO to natural gas was about 76% of the total emissions. The pollutants with the largest reduction in emissions were carbon dioxide, sulfur oxide, nitrogen oxide, and particular matter. RoPax ships produced most of the emissions, followed by cruise ships, regardless of whether the ship was sailing on MDO or LNG. The total pollutants were found to be the greatest in cruising mode, followed by hoteling mode, according to

Table A1. MDO: the amount of emissions (tons/year) produced during different operation modes (cruising (Cr), maneuvering (Man), and hoteling (Hotel)) by ship type and fuel type.

MDO
Ship Types	CO2			NOx			CO			HC			PM			SO2			CH4
	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel
Cruise Ships	9247.95	1320.69	3676.82	232.23	33.16	92.34	8.30	1.19	3.30	0.16	0.02	0.06	2.65	0.38	1.06	9.45	1.34	3.76	0.16	0.02	0.06
RoPax	48,827.75	11,331.25	45,324.99	1,226.15	284.56	1,138.25	43.83	10.20	40.67	0.82	0.23	0.82	14.06	3.28	13.01	49.93	11.60	46.29	0.82	0.23	0.82
Container Ships	2314.66	402.83	199.81	58.13	10.12	5.02	2.65	0.36	0.18	0.04	0.01	0.00	0.66	0.12	0.06	2.37	0.41	0.20	0.04	0.01	0.00
Vehicle Carriers	170.53	26.64	37.81	4.28	0.66	0.95	0.15	0.02	0.03	0.00	0.00	0.00	0.05	0.01	0.01	0.17	0.02	0.04	0.00	0.00	0.00
General Cargo	1473.05	147.98	367.84	36.99	3.72	9.24	1.32	0.13	0.33	0.03	0.00	0.01	0.43	0.04	0.11	1.50	0.15	0.37	0.03	0.00	0.01
Total	62,033.94	13,229.39	49,607.27	1557.78	332.22	1.245.80	56.25	11.90	44.51	1.05	0.26	0.89	17.85	3.83	14.25	63.42	13.52	50.66	1.05	0.26	0.89

and

Table A2. LNG: the amount of emissions (tons/year) produced during different operation modes (cruising (Cr), maneuvering (Man), and hoteling (Hotel)) by ship type and fuel type.

LNG
Ship Types	CO2			NOx			CO			HC			PM			SO2			CH4
	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel	Cr	Man	Hotel
Cruise Ships	1550.47	1071.00	2,981.68	38.16	5.45	15.17	28.14	3.86	8.58	2.48	0.35	1.00	0.09	0.02	0.03	0.08	0.02	0.03	87.91	12.56	34.95
RoPax	39,596.49	9188.95	36,755.91	201.47	46.76	186.93	148.61	33.05	132.44	13.13	3.05	12.19	0.47	0.12	0.47	0.47	0.12	0.35	464.23	107.71	430.94
Container Ships	1788.62	311.28	154.40	8.30	1.45	0.72	5.40	0.94	0.18	0.62	0.11	0.05	0.02	0.00	0.00	0.02	0.00	0.00	13.29	2.31	1.15
Vehicle Carriers	138.29	21.60	30.66	0.70	0.11	0.16	0.54	0.09	0.09	0.05	0.01	0.01	0.00	0.00	0.00	0.00	0.00	0.00	1.62	0.26	0.36
General Cargo	1138.27	114.35	284.24	5.29	0.53	1.32	3.44	0.35	0.85	0.40	0.04	0.10	0.02	0.00	0.00	0.02	0.00	0.00	0.01	0.85	2.11
Total	44,212.14	10,707.18	40,206.89	253.92	54.30	204.30	186.13	38.29	142.14	16.68	3.56	13.35	0.60	0.14	0.50	0.59	0.14	0.38	567.06	123.69	469.51

(see Appendix A). Ship hoteling emissions are concentrated close to the shore; as a result, it is essential to reduce air pollution within the proximity of coastal cities.

Ships are a source of air pollution in Heraklion, especially in terms of NOx, CO₂, and SO₂ emissions. However, because maritime transport is extremely energy efficient and because it is expected to increase significantly in the near future, emission mitigation strategies have been considered. More detailed and complex research into methods that can reduce the volume and quality of emissions from ships in port areas, such as scrubbers, selective catalytic reduction (SCR), exhaust gas recirculation (EGR) [52,53], biodiesel–acetylene [54], biofuels, hydrogen, ammonia, and battery power, will be the direction of our future research.