615

1 INTRODUCTION

Degradation of air quality and climate change are

perceived as the two biggest environmental concerns

for Europeans, due to the negative effects on human

health, productivity, and property. To reduce

emissions of greenhouse gases and air pollutants

holistic solutions are needed and efforts must be made

at local, regional, national, and global levels [5]. A

distinct combination of geographic, bathymetric,

orographic, climatic characteristics, and significant

anthropogenic pressures makes the Adriatic Sea

highly sensitive to pollution, and efforts to promote

the environmental sustainability of human activities

that affect it have been taken by the Croatian

government [13].

Historically, the focus of the prevention measures

has been on activities that occur at sea, where the

majority of airborne emissions occur, as can be seen in

Figure 1 for greenhouse gases (GHG) emissions [10].

However, efforts to make maritime transport less

polluting must include ports. The port emissions can

significantly contribute to air quality degradation of

urban areas [23]. Ships, as the single largest source of

port-related pollution, may pose an important health

risk in certain port cities. Namely, emissions of SO2

can be larger than those of road traffic, and emissions

of PM and NOx can be comparable with those of road

traffic and lead to negative health effects like asthma,

cardiovascular diseases, lung cancer, premature

mortality, and morbidity [1]. Furthermore, the “green

ports”, an answer to demands of environmentalists,

consumers, and government for more

Estimating Shipping Emissions – A Case Study for Cargo

Port of Zadar, Croatia

. Knežević, Z. Pavin & J. Čulin

University of Zadar, Zadar, Croatia

ABSTRACT: Reducing air pollutant emissions and energy consumption, as a necessary step to make ports more

sustainable, is one of the crucial tasks and challenges of port management. Some of the port strategies to meet

the term “green port” usually include reducing fuel consumption from vessels and vehicles in ports. This paper

estimates the emission inventory of maritime traffic for the cargo Port of Zadar. For this research, emissions

from cargo ships are estimated in the period from January 01. 2018 until October 01. 2019. The “bottom-up”

methodology has been applied for estimating emissions, which includes detailed data on the ship’s

characteristics (engine power, the load factor, fuel type, the emission factor) and time spent cruising and

hotelling. The emissions from cargo ships have been estimated for three ship’s activities: cruising in the reduced

speed zone, hotelling (time spent at berth), and maneuvering. The emission results (tons/year) refer to the

pollutants such as nitrogen oxides (NOx), sulphur oxides (SOx), particulate matter (PM), volatile organic

compounds (VOC), and carbon dioxide (CO2) which represents greenhouse gases. Estimating emission

inventory is the first step for planning effective port air quality control. Some recommendations for reducing

emissions in port areas are emphasized in this paper.

http://www.transnav.eu

the

International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 15

Number 3

September 2021

DOI: 10.12716/1001.15.03.16

616

environmentally sustainable movement of goods and

people, need to reduce GHG emissions. Moreover,

many measures for reducing GHG emissions also

reduce emissions of air pollutants and noise [22].

Figure 1. International GHG emissions (in CO2e) by

operational phase in 2018, according to the voyage-based

allocation of emissions [(3)3]

To develop measures to reduce emissions in the

ports it is necessary to estimate emissions from

visiting ships [22]. For that basic step, many data are

required: vessel parameter data, activity data,

operational data, and geographical domain data [8]. A

plethora of studies has been conducted to investigate

various aspects of ship emissions in ports, including

emission inventories for numerous ports [1, 17, 23].

On the national level, it is necessary to develop the

National Ships Emissions Inventory. Emission

inventories for several Croatian ports have been

published so far. Radonja et.al. [18] estimated

quantities of CO2, NOx, SOx and PM emitted at the

port of Rijeka in 2017, while Stazić et al. [21]

published emissions inventory of the port of Split

done for the same pollutants and year. The emission

inventory of marine traffic in the port of Šibenik in

2018, which included CO2, NOx, SOx, PM, and VOCs

has been estimated by Pastorčić et al. [15].

2 AREA OF RESEARCH AND PORT DATA

The emission trends analyzed in this paper are based

on the emission inventory of the cargo Port of Zadar

in two time periods, the first being the period from

January to December 2018 and the second being the

period from January to October 2019. The year 2020

wasn’t analyzed in this paper due to the effect of the

COVID-19 pandemic has had on shipping and was

thus concluded that the 2020 trend wouldn’t be

relevant in comparison with the usual trends. The

Zadar cargo port marine traffic has been generated in

Table 1 according to the data provided by Port of

Zadar Authority and Luka Zadar d.d. [11].

Table 1. Marine cargo traffic in the cargo Port of Zadar for

2018 and 2019 year

_______________________________________________

Period January 01- January 01-

December 31. 2018 October 01. 2019

_______________________________________________

Type of vessel Number Number Number Number

of vessels of arrivals of vessels of arrivals

_______________________________________________

General cargo 5 5 13 14

Bulk carrier 5 39 6 30

Tankers 19 20 9 23

Reefer 0 0 4 5

_______________________________________________

Figure 2. Cargo Port of Zadar: 1 – terminal for liquid cargo,

2 – oil platform supply terminal, 3 – terminal for bulk

carriers, 4 – terminal for general cargo, 5 and 6 – terminal

for general cargo and cement

The liquid cargo terminal is comprised of a 60 m

coastline (mooring up to 190 m in length), draft of 10.3

m to 12 m and the potentiality to moor ships up to

40,000 DWT. The terminal also consists of tanks for

petroleum products with the capacity of 60,000 m

tanks for chemicals with the capacity of 15,000 m

, 16

pipelines, and a floating protective barrier with a

length of 300 m. The oil platform supply terminal is

comprised of a 180 m coastline, a draft of 4.8 m to 7.1

m, closed warehouses and workshops, an open

storage area of 20,000 m

and a 9 m long ramp.

The bulk freight loading/unloading terminal is

comprised of a 140 m coastline, a 12 m draft with the

potentiality to moor ships up to 80,000 DWT. The

capacity of the terminal is 500,000 tons annually with

an unloading capacity of 500 tons/hour. The terminal's

construction provides a possibility to simultaneously

load wagons on two railway tracks. The terminal also

houses a grain silo with the capacity of 38,000 m3 and

closed storage with the capacity of 30,000 m3. The first

general cargo loading/unloading terminal is

comprised of a 135 m coastline, a draft of 7 m to 11.4

m, and the potentiality to moor ships up to 10.000

DWT.

The second general cargo loading/unloading

terminal is comprised of a 150 m coastline, a draft of

8.7 m to 10.2 m with the potentiality to moor ships up

to 20,000 DWT. The terminal uses a 24 m long RO-RO

ramp, an open storage area of 150,000 m2 and a closed

warehouse with an area of 34.000 m2. The terminal

also uses an industrial railway track with the capacity

of servicing 140 wagons per day. The cement

loading/unloading terminal has an annual capacity of

80,000 tons with the potentiality of unloading ships

from both general cargo piers, weighing max. up to 50

tons and distribution to trucks.

The distance a ship travels from the start of the

pilotage until its end at the port is defined as the

“Reduce speed zone”. The pilotage starts at the island

of Grujica and finishes at the Zadar port breakwater,

comprising a pilotage route of 35.245 Nm (64.588 km)

(Figure 3). The estimated maximum safe speed for

cargo ships in a reduced speed zone is 9 knots [24].

617

Figure 3. Reduce speed zone – pilotage of ships (Grujica-

Zadar)

3 METHODOLOGY

The applied method for estimating emissions from

maritime traffic in this paper is the so-called “bottom-

up” method. To estimate the quantity of each

pollutant emitted this method uses comprehensive

data such as the type and power of the main and

auxiliary engine, used fuel, engine load factor,

emission factor, and ship’s voyage data. The

guidelines for emission inventories [3, 6, 10, 24] are

mostly estimating emissions of NOx, SOx, PM, VOC,

HC pollutants, and CO2 as a greenhouse gas.

However, the latest edition of the IMO study [10]

emphasized the increase of methane (CH4) emissions

and black carbon emission, which is not a greenhouse

gas but a component of soot, emitted by the

incomplete combustion in engines and it is also

harmful to the atmosphere.

There are few different approaches for developing

a port emission inventory and they can sometimes

vary in terms of the research area, time, and available

resources. The usual difference is between the highly

detailed inventories which are typical for the

geographically larger ports with numerous ship calls

and the mid-tier approach which is often used for

smaller ports. In the detailed port inventories, the

emissions from the land-based activities are also

included. However, this approach is mainly used for

container terminals or ports with cargo handling

equipment, locomotives, and heavy-duty vehicles

[16].

This methodology estimates the total emissions

from the ship’s voyage by summing the emissions

from all the ship’s activities. One particular trip is

divided into three activities: cruising at sea,

maneuvering, and hotelling (at berth). For a single trip

emission can be calculated as:

T CMH

EEE E=++

The emissions from a ship in navigation are

expressed with the following equation [6]:

( ) ( )

C ME AE

E ME LF EF AE LF EF



=⋅ ⋅ ⋅+⋅ ⋅



For each ship calling in a port or during

maneuvering, the emissions for at berth and

maneuvering activities has been calculated as follows

[6]:

( ) ( )

H M ME AE

E E T ME LF EF AE LF EF



==⋅ ⋅ ⋅+⋅ ⋅



where:

E – emission (T-trip, C-cruising, M-manoeuvring, H-

hotelling) [g]

D – distance travelled (km)

v – average ship’s speed (km/h)

ME – installed main engine power (kW)

LFME – main engine load factor (%)

AE – installed auxiliary engine power (kW)

LFAE – auxiliary engine load factor (%)

EF – emission factor, depending on the fuel type and

ship’s speed (g/kWh)

t – hotelling and manoeuvring time (h)

3.1 Time activities

For more accurate estimation it is necessary to

determine the average time of each ship’s activity.

Each activity is associated with a different engine load

that has a unique emission factor. The cruising time

(in hours) refers to the slow steaming of the ship in a

reduced speed zone. Time is calculated in equation (2)

as the ratio of the trip’s length (km) and average speed

of cargo ships in a reduced speed zone, which is

estimated to 9 knots (16.67 km/h) [24].

The maneuvering activity is related to the area

between the breakwater and the dock. According to

the data obtained from the Port of Zadar authority,

the maneuvering time for bulk carriers, general cargo

ships, and reefers is 1 hour, while for tankers is 2

hours due to placing additional safety breakwaters.

The hotelling time implies the time ship spent at

berth (anchorage). Most of the guidelines for the port

emission inventories are estimating the hotelling time

according to the type of ship. This approach is useful

only for the ports with a large number of ships that

call throughout the year or in the case when the

information about hotelling time is uncertain. Based

on the data obtained from the Port of Zadar [11], the

total time at berth for each cargo ship is determined.

3.2 Fuel type and emission factors

The type of fuel used in main and auxiliary engines is

highly important when estimating exhaust gases

emissions. The exhaust emissions depend on the

sulphur and carbon content in the fuel. The sulphur

content in fuel is defined by EU directive 2016/802 [7]

which requires the use of low sulphur fuel (0.1%) in

all EU ports and the inland waters. This paper

assumes that ships use marine gas oil with a low

sulphur content that does not exceed 0.1% by mass.

The emission factors are commonly used for

estimating shipping emissions and they depend on

the type of engine, fuel used, the ship’s activity, and a

load factor of main and auxiliary engines. The main

engine emission factors are presented in Table 2 for

slow speed (SSD) and medium speed (MSD) diesel

engines.

618

Table 2. ME emission factors (g/kWh) ‘at sea’, ‘while

maneuvering, ‘at berth’ [3]

_______________________________________________

Engine type/ NOx pre- NOx post-

fuel type 2000 engine 2000 engine SO2 CO2 VOC PM

_______________________________________________

At sea

_______________________________________________

SSD/MGO 17.0 14.1 0.7 588 0.6 0.3

MSD/MGO 13.2 11.0 0.8 645 0.5 0.3

_______________________________________________

Manoeuvring / at berth

_______________________________________________

SSD/MGO 13.6 11.3 0.8 647 1.8 0.9

MSD/MGO 10.6 8.8 0.9 710 1.5 0.9

_______________________________________________

The NOx emission factors are determined

according to the IMO NOx Technical Code [14]

because engines installed on the ship before 01

January 2000 need to meet the required NOx emission

limit. From overall cargo ships arrived at the port in

2018, the 8 ships have engines installed before 2000,

and in 2019 the 13 ships. The auxiliary engine

emission factors are presented in Table 3, and they are

equal for all three ship’s activities.

Table 3. AE emission factors (g/kWh) ‘at sea’, ‘while

maneuvering, ‘at berth’ [3]

_______________________________________________

Engine type/ NOx pre- NOx post-

fuel type 2000 engine 2000 engine SO2 CO2 VOC PM

_______________________________________________

M/H SD/MGO 17.0 14.1 0.7 88 0.4 0.3

M/H SD/MDO 17.0 14.1 5.6 588 0.4 0.4

M/H SD/RO 14.7 12.2 12.3 722 0.4 0.8

_______________________________________________

3.3 Engine particulars and load factors

For a more precise calculation of emissions, it is

necessary to obtain the data of main and auxiliary

engine power (kW) and load factor for each cargo

ship. The data on the main and auxiliary engines have

been obtained from available ship particulars and

database [20]. The engine specifications from each

ship have shown that all cargo ships are mechanically

driven by two-stroke or four-stroke diesel engines.

The load factor of the main and auxiliary engine is

a percentage of the load in relation to the maximum

continuous rating (MCR). It depends on the actual

speed of the ship and different activities. The load

factor of the main engines, according to the literature

[3] is 80% while cruising, 20% during maneuvering

and for hotelling activity, it is assumed that main

engines are not running, except in the case of tanker

ships where the load factor is 20% due to usage of

transfer pumps. The auxiliary engine load factors

depend on the type of the ship and activity. The

highest load factors are during maneuvering activity

due to the usage of bow thrusters which increase

electrical energy supply. Moreover, it is assumed that

auxiliary engines are running at all the time, except

during hotelling if cold ironing is provided in port

(not in this case). The used auxiliary engine load

factors for each type of cargo ship and activity are

presented in Table 4.

Table 4. Auxiliary engine load factors for cargo ships [24]

_______________________________________________

Vessel type Cruise Reduce Manoeuvre At berth

speed zone

_______________________________________________

General cargo 0.17 0.27 0.45 0.22

Bulk carrier 0.17 0.27 0.45 0.22

Container ship 0.13 0.25 0.50 0.17

Tanker 0.13 0.27 0.45 0.67

Reefer 0.20 0.34 0.67 0.34

_______________________________________________

4 RESULTS

The total annual emissions in 2018 are 48.52 t for NOx,

2.45 t for SOx, 1.40 t for PM, 2.57 t for VOC, and in

2019 is 39.04 t for NOx, 1.90 t for SOx, 1.14 t for PM,

and 2.14 t for VOC (Figure 4). The emission results in

Figures 4 and 5 have been displayed for each

pollutant and ship’s activity. For 2019 the total annual

emissions results are: 39.04 t for NOx, 1.90 t for SOx,

2.14 t for VOC, 1.14 t for PM (Figure 5).

Figure 4. Cargo ship emissions in 2018 for each activity

Figure 5. Cargo ship emissions in 2019 for each activity

Figure 6. Total CO2 emission for 2018 and 2019

The CO2 emissions of cargo traffic for 2018 and

2019 are shown in Figure 6. Cargo ships emitted

2069.18 tons of CO2 in 2018 and 1612.23 tons in 2019.

Obviously, the lowest amount of emission is during

maneuvering activity due to the short time and low

main engine load factors. The highest quantity of CO2

is emitted during cruising due to high load factors

619

and installed power of the main engines. The auxiliary

engines are responsible for the emissions during

hotelling activity and with longer time spent at berth,

they are almost as emissions during cruising (2018-

cruising 1040.86 t, maneuvering 942.69 t and in 2019 –

cruising 854.13 t, maneuvering 701.40 t).

5 DISCUSSION

The results show that most of the emission is

generated during cruising activity and a notable part

is the result of hotelling activity. The emissions during

hotelling and maneuvering have a more significant

impact on the port area climate and human health.

Most of the emissions in port are from auxiliary

engines, due to increased ship’s electricity demands.

The electricity demand depends on the type of cargo

ship, for example, tankers are using electricity for

transfer cargo pumps and general cargo ships for

loading/unloading the cargo.

In Figure 6 the emissions are divided according to

the type of cargo ship. The majority of emissions are

produced by tankers (70%) and general cargo ships

are responsible for 20%. The main reason why tankers

have the highest emissions is due to large installed

power (kW), especially of the two-stroke low-speed

main engine. The bulk carriers had more port calls

than tankers in 2018 and 2019, however, their main

engines are mostly high-speed four-stroke engines.

Also, the auxiliary engine load factor (at berth) for

tanker ships is higher than the rest of the cargo ships.

Figure 7. Overall CO2 emissions for a different type of cargo

ships (2018 and 2019)

To achieve the term “green port” the port

authorities must find the solution for reducing

pollution from ships while at berth, moreover, the

ship-owners must adapt to the sustainable energy-

efficient plan of each port. The emission reduction in

port depends on many factors such as port size,

number of port calls, type of port, financial condition,

and local infrastructure. Few recommended measures

for reducing emissions in the port:

− Cold ironing (On-shore power supply)

The meaning of “cold ironing” term is when shore-

side electric power is provided to ships while at

berth, allowing them to shut down the auxiliary

engines. This measure can significantly reduce

emissions in port, however, it depends on the

source of electric energy. The ideal scenario is

when the port power grid is supplied through

renewable energy sources. For ports in the EU

where air quality is above normal and with a high

level of noise the EU recommendation 2006/339/EC

[4] for shore-side electricity is provided. Few

examples of large ports in Europe [9, 19] that are

using cold ironing are the ports of Gothenburg,

Antwerp, Stockholm, Bergen.

− Alternative fuels

The most efficient method for reducing emissions

without installing any technologies on the ship is

to change fuel from marine diesel oil to cleaner

fuels. The existing alternative fuels for the

shipping industry are LNG (Liquefied Natural

Gas), LPG (Liquefied Petroleum Gas), NH3

(Ammonia), CH3OH (Methanol), H2 (Hydrogen),

HVO (Hydrotreated Vegetable Oil) [2]. When

compared with conventional diesel oil, alternative

fuels can significantly reduce SOx, NOx, and PM

emissions because they primarily depend on fuel

used. However, the main difficulties for operating

with alternative fuels are in economical aspects

such as energy cost, capital cost, and availability.

For most of the alternative fuels, current

availability is insufficient to cover the energy

consumption for the shipping industry and most

ports are lacking the necessary infrastructure and

bunkering stations.

− Slow steaming and reduced time in port

The reduction of sailing speed or so-called ‘slow

steaming’ has become common for many cargo

ships, especially containers to save bunker fuel

costs. Slow steaming is an effective method for

reducing CO2 emissions and it could be achieved

without installing any new technology. However,

in fairway channels or in this case, in reduced

speed zone, the ships are already going slow so

further speed reduction could increase the fuel

consumption or even damage the main engine and

increase maintenance costs. The normal operating

range for main engines is 70-85% of MCR and

while slow steaming is up to 50 to 55% [12].

Another operating measure for reducing emissions

in port is to reduce time spent at berth. This could

be done with more efficient administrative

procedures, port operations, optimized

loading/unloading activity, and improved

communication between ship crew and port

authorities. As seen in results the emissions at

berth are mostly from the auxiliary engines, so this

measure could have the potential for ships with

large installed auxiliary power that spends a long

time in port.

6 CONCLUSION

The annual exhaust emissions in 2018 and 2019 year,

generated by different types of cargo ships in the

cargo Port of Zadar, have been estimated by the

‘bottom-up’ methodology. This methodology divides

the estimated emissions into three activities (cruising,

maneuvering hotelling), of which activity hotelling

has a significant impact on the port air quality. The

overall marine cargo traffic included 64 port calls in

2018. and 72 in 2019. Bulk carriers emitted 20% of

total emissions and the highest amount of emissions

620

are from tanker ships (70%) due to large main and

auxiliary engine power and 43 port calls in two years.

The obtained results are necessary to prepare the

emission database and then to determine the

sustainable plan for reducing emissions in port.

Moreover, the results are contributing to emission

inventory on a national level and they could be

compared with inventories in other Croatian cargo

and passenger ports. To reach sustainable and energy-

efficient objectives, the previously mentioned

measures for reducing should be considered not only

on a local level but also on a regional and national

level.

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