10
Atmospheric Environment 37 (2003) 2139–2148 Emissions of trace gases and particles from two ships in the southern Atlantic Ocean Parikhit Sinha a , Peter V. Hobbs a, *, Robert J. Yokelson b , Ted J. Christian b , Thomas W. Kirchstetter c , Roelof Bruintjes d a Department of Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98195 1640, USA b Department of Chemistry, University of Montana, Missoula, USA c Lawrence Berkeley National Laboratory, Berkeley, CA, USA d National Center for Atmospheric Research, Boulder, CO, USA Received 2 September 2002; accepted 9 January 2003 Abstract Measurements were made of the emissions of particles and gases from two diesel-powered ships in the southern Atlantic Ocean off the coast of Namibia. The measurements are used to derive emission factors from ships of three species not reported previously, namely, black carbon, accumulation-mode particles, and cloud condensation nuclei (CCN), as well as for carbon dioxide, carbon monoxide (CO), methane (CH 4 ), non-methane hydrocarbons, sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), and condensation nuclei. The effects of fuel grade and engine power on ship emissions are discussed. The emission factors are combined with fuel usage data to obtain estimates of global annual emissions of various particles and gases from ocean-going ships. Global emissions of black carbon, accumulation- mode particles, and CCN from ocean-going ships are estimated to be 19–26 Gg yr 1 , (4.4–6.1) 10 26 particles yr 1 , and (1.0–1.5) 10 26 particles yr 1 , respectively. Black carbon emissions from ocean-going ships are B0.2% of total anthropogenic emissions. Emissions of NO x and SO 2 from ocean-going ships are B10–14% and B3–4%, respectively, of the total emissions of these species from the burning of fossil fuels, and B40% and B70%, respectively, of the total emissions of these species from the burning of biomass. Global annual emissions of CO and CH 4 from ocean-going ships are B2% and B2–5%, respectively, of natural oceanic emissions of these species. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Ship emissions; Particles from ships; Gases from ships; Emissions from ships; Pollution from ships 1. Introduction Ships are among the world’s highest polluting combustion sources per quantity of fuel consumed (Corbett and Fischbeck, 1997). They account for up to B14% of all nitrogen emissions from fossil fuel combustion, and up to 4% of all sulfur emissions from fossil fuel combustion (Corbett et al., 1999). Moreover, ship emissions often take place in areas remote from other sources of air pollution. Over large areas of the northern hemisphere, and in some regions of the southern hemisphere, sulfur emissions from ships are comparable to natural biogenic emissions of dimethyl sulfide (DMS) from the ocean (Corbett et al., 1999). Emissions from ships may increase surface concentra- tions of nitrogen oxides (NO x ) in heavily traversed ocean regions by more than 100-fold (Lawrence and Crutzen, 1999). Cloud condensation nuclei (CCN) in ship exhausts can increase the albedo of stratiform marine clouds by increasing the concentrations of cloud droplets *Corresponding author. Tel.: +1-206-543-6027; fax: +1- 206-685-7160. E-mail address: [email protected] (P.V. Hobbs). 1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1352-2310(03)00080-3

Emissions of trace gases and particles from two ships in the southern Atlantic Ocean

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Atmospheric Environment 37 (2003) 2139–2148

Emissions of trace gases and particles from two ships in thesouthern Atlantic Ocean

Parikhit Sinhaa, Peter V. Hobbsa,*, Robert J. Yokelsonb, Ted J. Christianb,Thomas W. Kirchstetterc, Roelof Bruintjesd

aDepartment of Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98195 1640, USAbDepartment of Chemistry, University of Montana, Missoula, USA

cLawrence Berkeley National Laboratory, Berkeley, CA, USAdNational Center for Atmospheric Research, Boulder, CO, USA

Received 2 September 2002; accepted 9 January 2003

Abstract

Measurements were made of the emissions of particles and gases from two diesel-powered ships in the southern

Atlantic Ocean off the coast of Namibia. The measurements are used to derive emission factors from ships of three

species not reported previously, namely, black carbon, accumulation-mode particles, and cloud condensation nuclei

(CCN), as well as for carbon dioxide, carbon monoxide (CO), methane (CH4), non-methane hydrocarbons, sulfur

dioxide (SO2), nitrogen oxides (NOx), and condensation nuclei. The effects of fuel grade and engine power on ship

emissions are discussed. The emission factors are combined with fuel usage data to obtain estimates of global annual

emissions of various particles and gases from ocean-going ships. Global emissions of black carbon, accumulation-

mode particles, and CCN from ocean-going ships are estimated to be 19–26Gg yr�1, (4.4–6.1)� 1026 particles yr�1, and

(1.0–1.5)� 1026 particles yr�1, respectively. Black carbon emissions from ocean-going ships are B0.2% of total

anthropogenic emissions. Emissions of NOx and SO2 from ocean-going ships are B10–14% and B3–4%, respectively,

of the total emissions of these species from the burning of fossil fuels, and B40% and B70%, respectively, of the total

emissions of these species from the burning of biomass. Global annual emissions of CO and CH4 from ocean-going

ships are B2% and B2–5%, respectively, of natural oceanic emissions of these species.

r 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Ship emissions; Particles from ships; Gases from ships; Emissions from ships; Pollution from ships

1. Introduction

Ships are among the world’s highest polluting

combustion sources per quantity of fuel consumed

(Corbett and Fischbeck, 1997). They account for up to

B14% of all nitrogen emissions from fossil fuel

combustion, and up to 4% of all sulfur emissions from

fossil fuel combustion (Corbett et al., 1999). Moreover,

ship emissions often take place in areas remote from

other sources of air pollution. Over large areas of the

northern hemisphere, and in some regions of the

southern hemisphere, sulfur emissions from ships are

comparable to natural biogenic emissions of dimethyl

sulfide (DMS) from the ocean (Corbett et al., 1999).

Emissions from ships may increase surface concentra-

tions of nitrogen oxides (NOx) in heavily traversed

ocean regions by more than 100-fold (Lawrence and

Crutzen, 1999).

Cloud condensation nuclei (CCN) in ship exhausts

can increase the albedo of stratiform marine clouds

by increasing the concentrations of cloud droplets

*Corresponding author. Tel.: +1-206-543-6027; fax: +1-

206-685-7160.

E-mail address: [email protected]

(P.V. Hobbs).

1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S1352-2310(03)00080-3

(Twomey, 1977; Radke et al., 1989; King et al., 1993;

Ferek et al., 1998). The resulting ‘‘ship tracks’’ appear in

satellite imagery as long-lived linear regions of enhanced

solar reflectivity in marine stratiform clouds downwind

of ships (Hobbs et al., 2000). Global radiative forcing

due to the emission of CCN from ships has been

estimated to be –0.11Wm�2 (Capaldo et al., 1999).

Emissions of NOx from ships increase tropospheric

ozone (O3) and the hydroxyl radical (OH) over their

background levels, thereby increasing the oxidizing

power of the troposphere, decreasing the atmospheric

lifetimes of reactive greenhouse gases, and increasing

aerosol production rates (Lawrence and Crutzen, 1999).

Since B70% of the emissions from ocean-going ships

occur within 400 km of land, ship emissions may also

affect air quality in many coastal and port regions

(Corbett et al., 1999).

A global inventory of ship emissions, based on

emission measurements at sea, fuel usage, and engine

characteristics, has been given by Corbett et al. (1999).

Emission factors (i.e., mass of a species emitted per unit

mass of fuel burned) based on emission tests from

Lloyd’s Register of Shipping are given by Carlton et al.

(1995). Emission factors for some species have been

obtained from airborne measurements in the plumes of

ships at sea (Hobbs et al., 2000).

In September 2000, the University of Washington

(UW) Cloud and Aerosol Research Group (CARG),

with its Convair-580 research aircraft, obtained in situ

measurements of a large number of gaseous and

particulate emissions, including several species not

previously measured, from two ships in the southern

Atlantic Ocean, off the coast of Namibia. These

measurements are described here and utilized to derive

estimates of emissions of a number of species from

ocean-going ships worldwide.

2. Sampling techniques and instrumentation

All of the measurements described in this paper were

obtained aboard the UW Convair-580 research aircraft.

A complete list of the instruments aboard this aircraft

for the present study is given in a technical appendix by

P.V. Hobbs in Sinha et al. (2003). Only the instruments

and techniques that provided the measurements pre-

sented in this paper are described here.

Aerosol samples collected on quartz filters (Pallflex

2500 QAT-UP) were used to determine the concentra-

tion of particulate carbon. Black carbon (BC) concen-

tration was measured with an optical transmission

technique similar to that described by Rosen and

Novakov (1983). This method compares the attenuation

of white light through a loaded filter relative to that of a

blank filter. The relationship between optical attenua-

tion (ATN) and the BC concentration (mg cm�2) is given

by ATN=sBC, where ATN ¼ 100� ln ðI0=IÞ; where I0and I are the transmitted light intensities through the

blank and loaded filters, respectively, and s the mass

absorption cross-section for BC deposited on quartz

(m2 g�1). A value of 20m2 g�1 was used for the mass

absorption cross-section (Gundel et al., 1984).

Measurements of SO2 were made using a Teco model

43S pulsed-fluorescence analyzer (precision of 7%,

detection limit of 1 ppbv). Calibration of this instru-

ment, both in flight and on the ground, was carried out

with commercial standard mixture (Scott-Marrin) of

18079 ppbv SO2 in ultra pure air. The instrument was

zeroed using ultra pure air (SO2o1 ppbv). Measure-

ments of O3 were obtained with a Teco model 49C UV

photometric analyzer (precision of 2%, detection limit

of 3 ppbv). Calibration of this instrument was carried

out prior to and following the field project using a

Columbia Scientific Instruments Photocal 3000 Version

080 Ozonator. Continuous measurements of O3 were

obtained using the Teco 49C in ambient air.

The total concentration of particles (CN) in the size

range B0.003–3mm diameter was measured with a TSI

3025A ultrafine condensation particle counter (precision

of 10%). A particle measuring systems (PMS) passive

cavity aerosol spectrometer probe (PCASP-100X) was

used for measuring particle size spectra from B0.10 to

3.00 mm. The PCASP-100X was mounted on the wing of

the aircraft. The sampling inlet was heated to dry the

particles, so that measurements from the PCASP could

be compared with those obtained on dried particles with

other instruments inside the aircraft cabin. The PCASP-

100X was regularly calibrated on the ground using

polystyrene latex spheres of known sizes. Concentra-

tions of cloud condensation nuclei (CCN) at 0.3%

supersaturation were measured with a University of

Wyoming thermal diffusion chamber.

The filters, SO2, and O3 measurements required

sampling times longer than it took the aircraft to cross

the widths of ship plumes (B30 s). Therefore, when

sampling the plumes, we employed a ‘‘grab-bag’’

technique, which consisted of a 2.5m3 electrically

conducting plastic (Velostat) bag that could be filled

with a sample of a plume in 12 s, to obtain samples for

the filters, SO2 and O3 measurements. Samples in the

grab-bag were drawn through the filters for subsequent

chemical analysis of the aerosol. The TSI 3025A was

also configured so it could sample from the grab-bag.

The grab-bag system had an aerosol 50% cut point

diameter of B4mm; larger particles were lost in the inletand on the walls of the grab bag. Grab-bag samples of

plumes were followed by grab-bag samples of ambient

air, which were compared to continuous sampling of

ambient air. There was no significant difference between

the two sampling techniques.

Evacuated electropolished stainless steel canisters

were used to sample the ship plumes, or ambient air

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–21482140

just upwind of the ships, using a stainless steel inlet that

passed through the aircraft fuselage. For each canister

sample, mixing ratios of selected C2–C11 non-methane

hydrocarbons (NMHC) were determined by gas chro-

matography (GC) with flame ionization detection (FID)

and electron capture detection (ECD). The precision of

the NMHC measurements was 3%, and the typical

NMHC detection limit was 3 pptv. Mixing ratios of CO2

(precision of 3%), CO (precision of 5%), and CH4

(precision of 0.1%) in the canisters were determined

using a second GC/FID. A detailed description of the

analytical procedure for the canister samples, including

quantification of the measurement precision for indivi-

dual compounds, is given by Colman et al. (2001).

An airborne Fourier transform infrared spectrometer

(AFTIR) was deployed onboard with a separate and

specially coated inlet that directed ram air through a

Pyrex multipass cell with an exchange time of 4–5 s. For

the ship plume penetrations, the AFTIR was used to

measure CO2, CO, nitric oxide (NO), nitrogen dioxide

(NO2), and O3. The AFTIR technique is described in

detail by Yokelson et al. (2003).

3. Calculation of emission factors

Emission factors for gases and particles were calcu-

lated using the carbon balance method (Radke et al.,

1988), which assumes that all carbon is emitted as CO2,

CO, CH4, non-methane organic compounds (NMOC),

and particulate carbon (PC). The emission factor

(EF(X)) of a species X is defined here as the ratio of

the excess mass concentration (DX ) of X emitted by a

source to the excess mass concentration of the total

carbon (DC) emitted by the source:

EF ðX Þ ¼

½DX �½DC�CO2

þ ½DC�CO þ ½DC�CH4þ ½DC�NMOC þ ½DC�PC

;

ð1Þ

where the excess mass concentration refers to the excess

in the plume over the concentration in the ambient air.

This emission factor is commonly converted to grams of

X emitted per kilogram of fuel burned using the mass

fraction of carbon in the fuel. Typically, the fuel burned

in large marine diesel engines is a mixture of hydro-

carbons with a ratio of hydrogen to carbon atoms of 1.8

(Tuttle, 1995), which corresponds to a mass fraction of

carbon in the fuel of B87%.

4. Ships studied

The UWs Convair-580 was used to sample emissions

from two ships: the tanker Royal Sphere, located at

26.25S and 13.49E, and the container ship MSC

Giovanna, located at 26.00S and 13.61E, both in the

southern Atlantic Ocean off the coast of Namibia

(Fig. 1). Plume samples of the Royal Sphere and the

MSC Giovanna were obtained at 1001 and 1033 UTC, 14

September 2000, respectively. Information on the two

ships is given in Table 1.

Diesel propulsion systems on large ships are designed

to run on two types of fuel, residual fuel and distillates.

Residual fuel refers to a broad category of low-grade

fuel, ranging from crude oil to a fuel where some of the

impurities have been removed from the oil, particularly

those that cause excessive engine wear. Residual fuels

are generally characterized by high density, high

viscosity, and high concentrations of impurities such as

sulfur (Corbett et al., 1999). The high viscosity fuel

carried on the Royal Sphere (2187 ton) is a residual fuel

that has only a few impurities removed. The inter-

mediate fuel oil carried on the MSC Giovanna (1906 ton)

is a higher grade of residual fuel with more impurities

removed. Distillates, such as the diesel oil carried on the

Royal Sphere (420 ton) and MSC Giovanna (309 ton), are

refined fuels of various grades that are more expensive

than residual fuels. Different engines require different

grades of distillates. Combustion of distillates results in

less non-CO2 emissions than the combustion of residual

fuels.

In general, ship operators use the lowest grade, lowest

cost fuel available that does not cause excessive engine

wear. When operating in the open ocean, ship operators

will generally use residual fuels. Due to their higher cost,

distillates are generally used only where air pollution

regulations require them (i.e., in harbors, on approaches

to major ports, and within certain distances from shore).

When ships make port visits only a few days apart, they

may continue to burn distillates during transit to avoid

switching between fuel systems. Based on their north-

northeast headings, both the Royal Sphere and the MSC

Giovanna appeared to be traveling toward the port at

Walvis Bay, Namibia (Fig. 1).

5. Results

5.1. Ambient conditions

Immediately prior to sampling the plumes from the

two ships, there were no clouds in the vicinity of the

ships, and there were no low-altitude stable layers to

limit the rise of the ship plumes. Surface wind speeds

were moderate at B10m s�1. The background air was

quite clean, with surface O3 mixing ratios below 30 ppbv,

surface SO2 mixing ratios of o1 ppbv, CN concentra-

tions of B500 cm�3, and CCN concentrations at 0.3%

supersaturation of B70 cm–3.

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–2148 2141

5.2. CN concentrations along the plumes

Measurements of CN concentrations along the length

of the two ship plumes are shown in Fig. 2a. The CN

concentrations in the plume from the Royal Sphere

peaked at B7� 104 cm�3 above the ship and dropped

off to ambient (B500 cm�3) concentrations B1 km

downwind of the ship. The CN concentrations in the

plume from the MSC Giovanna peaked atB1� 105 cm–3

above the ship and remained well above ambient

concentrations (5� 102 cm�3) up to at least 3 km down-

wind of the ship. The dense particulate emissions from

the MSC Giovanna were likely due to its use of residual

fuel.

5.3. Emission factors

Emission factors for selected gaseous and particulate

species were derived from the measurements obtained in

the plumes of the Royal Sphere and MSC Giovanna

(Table 2). As can be seen from Table 2, the SO2 emission

factor for the Royal Sphere was substantially less than

for the MSC Giovanna. We surmise from this that the

Royal Sphere had switched to distillate fuel as it headed

for port, but the MSC Giovanna was still burning

residual fuel.

In Table 2 the emission factors from this study are

compared with those for the ships discussed by Hobbs

et al. (2000) and Carlton et al. (1995). Hobbs et al.

derived emission factors for selected gases and particles

from in situ aircraft measurements of ship emissions off

the west coast of the United States. They sampled the

plumes of eight ships burning either low-grade marine

fuel oil or high-grade navy distillate fuel. Carlton et al.

(1995) describe the results of a study of ship emissions

from marine diesel propulsion engines conducted by

Lloyd’s Register of Shipping. Steady-state emissions at

various ship engine loads from 60 engines on 50 vessels

at sea were measured for medium- and slow-speed diesel

engines burning both distillate and residual fuel.

5.3.1. Carbon dioxide

Emissions of CO2 from ships are independent of

engine power and depend primarily on the carbon

Fig. 1. Locations of the Royal Sphere and MSC Giovanna when their plumes were sampled from the Convair-580 aircraft. The arrows

indicate the headings of the ships.

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–21482142

content of the fuel burned (Carlton et al., 1995). As

such, the emission factors for CO2 from the Royal

Sphere and MSC Giovanna (3135 and 3176 g kg�1 of

fuel, respectively) agree within 1% even though the

engine power of the MSC Giovanna exceeds that of the

Royal Sphere by B60% (Table 1). The CO2 emission

factors from this study are consistent with the value of

3170 g kg�1 of fuel reported by Carlton et al. (1995). The

CO2 measurements in this study were obtained by

AFTIR from plume samples collected at altitudes of

B90 and B60m above the Royal Sphere and MSC

Giovanna, respectively. The CO2 measurements from

Carlton et al. were obtained using a non-dispersive

infrared analyzer with a sample line directly attached to

the exhaust stack of the ship being studied.

The CO2 emission factors from this study can be

compared to the value of 1700760 g kg�1 of fuel

obtained by Sinha et al. (2003) for savanna fires in

southern Africa using the same instrumentation and

sampling strategies used in the present study. The much

higher CO2 emission factor for ships is primarily a result

of the higher carbon fraction in ship fuels (B87%)

compared to biomass (B50%).

5.3.2. Carbon monoxide

Unlike CO2, emissions of CO from ships are

dependent on engine power with higher CO emissions

resulting from ship engines with less power (Carlton

et al., 1995). As such, the CO emission factor for the

Royal Sphere (19.5 g kg�1 of fuel) exceeds that of the

MSC Giovanna (3.0 g kg�1 of fuel) whose engine is

B60% more powerful than that of the Royal Sphere.

Carlton et al. (1995) reported an average CO emission

factor of 7.4 g kg�1 of fuel, which is between the two

values measured in this study. Carlton et al. studied

ships with engine power ranging from 0.364 to

21.643MW, compared to the range of 8.2–13.4MW in

this study.

5.3.3. Hydrocarbons

As with CO, emissions of hydrocarbons (HC) from

ships depend on engine power, with lower power engines

emitting more HC. This trend is evident in the emission

factors for CH4 and NMHC, since the emission factors

for CH4 and NMHC for the Royal Sphere (5.4 and

2.4 g kg�1 of fuel, respectively) exceed those for the MSC

Giovanna (2.6 and 0.4 g kg�1 of fuel, respectively).

The emission factor for total hydrocarbons

(CH4+NMHC) reported by Carlton et al. (1995) of

2.4 g kg�1 of fuel is comparable to our measurement for

the MSC Giovanna (3.0 g kg�1 of fuel) but lower than

that of the Royal Sphere (7.8 g kg�1 of fuel). However,

hydrocarbon emissions depend not only on engine

power but also on the percentage utilization of engine

power. Carlton et al. (1995) showed that hydrocar-

bon emissions could be increased by B50% when theTable1

Propulsionsystem

parametersfortheships

Ro

ya

lS

ph

ereand

MS

CG

iova

nn

afrom

Lloyd’sRegisterofShipping(2002)

Ship

Ship

type

Gross

tonnage

Engine

type

Number

of

cylinders

Length

(m)

Beam

(m)

Draft(m

)Power

(MW)

Fuelaboard

Fuel

consumption

rate(kgs�

1)

Servicespeed

(ms�

1)

Ro

ya

l

Sp

her

e

Tanker

21,893

Diesel

6182.6

29.6

10.6

8.2

Dieseloil(420ton),

highviscosity

fuel

(2187ton)

0.35

7.9

MS

C

Gio

van

na

Container

27,103

Diesel

6177.6

32.2

10.7

13.4

Dieseloil(309ton),

interm

ediatefueloil

(1906ton)

0.49

9.4

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–2148 2143

percentage utilization changes from 85% to 25%. Since

the Royal Sphere was heading to port at Walvis Bay,

Namibia, it may well have slowed its speed and

decreased its percentage utilization of engine power,

resulting in higher hydrocarbon emissions.

5.3.4. Nitrogen oxides

Emissions of NOx from ships have been estimated to

account for up to B14% of nitrogen emissions from

fossil fuel combustion (Corbett et al., 1999), and hence

they are of global importance. Since NOx emissions

from ships are temperature-dependent, and more power-

ful combustion systems operate at higher temperatures,

the emission rate of NOx depends on the power of the

ship engine. The Royal Sphere and MSC Giovanna both

have six cylinder diesel engines, but since the MSC

Giovanna’s engine has 60% more power than the

Royal Sphere, the NOx emission factor for the MSC

Giovanna was greater than that from the Royal Sphere

(Table 2).

The high concentrations of NOx in the plumes from

the Royal Sphere and MSC Giovanna are consistent with

the much lower concentrations of O3 in the exhaust

directly above the ships (5–8 ppbv) than ambient O3

concentrations (23–27 ppbv), as measured by the Teco

49C. In the ship plumes, NO can react with O3 to form

NO2 and O2, thereby lowering O3 concentrations.

Downwind of the ships, the NOx, hydrocarbons, and

CO from ships (and other sources) react photochemi-

cally to form O3. Since O3 is an OH precursor, elevated

0 1 2 3 4 5 6 7

0

2

4

6

8

10 Royal SphereMSC Giovanna

CN

co

nce

ntr

atio

n (

in u

nits

of 1

04

cm-3)

Distance downwind of ship (km)

0.1 10.1

1

10

100

1000

10000

0.5

Royal SphereMSC GiovannaAmbient air

dN

/d(lo

gD

) (c

m-3)

Particle diameter D (micrometers)(b)

(a)

Fig. 2. (a) Condensation nucleus concentrations along the length of the plumes from the Royal Sphere, and the MSC Giovanna. (b)

Particle size distributions in the plumes directly above the Royal Sphere and MSC Giovanna and in the ambient marine air.

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–21482144

O3 downwind of ships will result in elevated OH and

increase the oxidation potential of the troposphere.

5.3.5. Sulfur dioxide

Sulfur dioxide emissions from ships are primarily

determined by the sulfur content of the fuel burned, so

that residual fuels produce higher SO2 emissions than

distillate fuels. Since the SO2 emission factor that we

derived for the MSC Giovanna (52.2 g kg�1 of fuel)

greatly exceeds that of the Royal Sphere (2.9 g kg�1 of

fuel), we conclude that at the time we sampled their

exhausts the Royal Sphere and MSC Giovanna were

burning distillate and residual fuels, respectively.

Carlton et al. (1995) reported SO2 emission factors for

ships in the form:

Emitted SO2 ðin g kg�1 of fuelÞ

¼ 20� ðpercentage of sulfur by weight in the fuelÞ: ð2Þ

Since marine fuel specifications require that residual

fuels have a maximum sulfur content of 5% by weight,

and that distillate fuels have a maximum sulfur content

of 2% by weight (IOS, 1987), typical upper limits for

SO2 emission factors for the burning of residual and

distillate fuel from Eq. (2) are: 100 and 40 g kg�1 of fuel,

respectively. Also, from (2) and the SO2 emission factors

measured in this study for the Royal Sphere and MSC

Giovanna, the percentage of sulfur by weight in the fuels

of the Royal Sphere and MSC Giovanna are deduced to

be 0.1% and 2.4%, respectively. The derived sulfur

fraction of the fuel used by the MSC Giovanna (2.4%)

exceeds the maximum specified sulfur content of

distillate fuels (2%) which further confirms our deduc-

tion that the MSC Giovanna was burning residual fuel at

the time of our measurements.

Hobbs et al. (2000) also found SO2 emission factors

from ships burning distillate fuel (6–24 g kg�1 of fuel) to

be substantially lower than for those burning residual

fuel (62725 g kg�1 of fuel). Substituting the SO2

emission factors given by Hobbs et al. (2000) into

Eq. (1), the percentages of sulfur by weight in distillate

and residual fuels used by the ships studied by Hobbs

et al. are deduced to be 0.3–1.1% and 2.871.1%,

respectively.

5.3.6. Black carbon

A single quartz filter was exposed to the exhausts from

both the Royal Sphere and MSC Giovanna. Analysis of

this filter yielded an average emission factor for black

Table 2

Emission factors of some gases and particles from the ships Royal Sphere and MSC Giovanna. Emission factors have units of grams of

species emitted per kilogram of fuel burned, except for CN, CN0.1–3mm, and CCN which have units of number of particles emitted per

kilogram of fuel burned

Fuel type Technique used for

measurement in this

studya

Royal Sphereb

(assumed to be

distillate fuel)

MSC Giovannac

(assumed to be

residual fuel)

Hobbs et al. (2000) Carlton et al. (1995)

Distillate fuel Residual fuel Residual and distillate

fuels

CO2 AFTIR 3135794 3176795 3170

CO GC/C 19.571.0 3.070.2 7.4

CH4 GC/C 5.470.1 2.67o0.1

NMHC GC/C 2.470.1 0.47o0.1

HC GC/C 7.870.2 3.070.1 2.4

NOx (as NO) AFTIR 22.371.1 65.573.3 2375 57–87

SO2 Teco 43S/GB 2.970.2 52.273.7 6–24 62725 20� (percentage of

sulfur by weight in

fuel)d

Black carbon Filter/GB (0.1870.02)e

CN TSI-3025A/GB (4.070.4)� 1016 (6.270.6)� 1016 (0.4–1.3)� 1016 (1.670.5)� 1016

CN0.1–3mm PMS PCASP-100X (1.170.1)� 1015 (5.170.5)� 1015

CCN (at 0.3%

supersaturation)

Thermal diffusion

chamber

(7.670.8)� 1014 (1.170.1)� 1015

aAFTIR=Airborne Fourier Transform Infrared Spectrometer; GC/C=gas chromatography via canisters; GB=grab bag.bEmission factors for the Royal Sphere are based on excess concentrations in the plume of 2.97 ppmv CO2, 29 ppbv CO, 14 ppbv

CH4, 6 ppbv NMHC, 31 ppbv NOx, 1.9 ppbv SO2, 0.6 mgm–3 black carbon, 7.18� 1010m�3 CN, 1.93� 109m–3 CN0.1�3 mm, and

1.35� 109m–3 CCN.cEmission factors for the MSC Giovanna are based on excess concentrations in the plume of 2.71 ppmv CO2, 4 ppbv CO, 6 ppbv

CH4, 1 ppbv NMHC, 82 ppbv NOx, 30.6 ppbv SO2, 0.6 mgm–3 black carbon, 9.94� 1010m–3 CN, 8.14� 109m–3 CN0.1–3mm, and

1.75� 109m–3 CCN.d In units of g kg�1 of fuel.eOne filter for black carbon analysis was exposed to the plumes from both ships.

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–2148 2145

carbon for the two ships of 0.18 g kg�1 of fuel. To our

knowledge, this is the first measurement of the emission

factor of black carbon from ocean-going ships. Carlton

et al. (1995) reported emission factors for total parti-

culate matter (TPM) from ships of 1.3 and 8.4 g kg�1 of

fuel burned for distillate fuel and residual fuel,

respectively. Taking the ratio of emission factors for

black carbon from this study and TPM given by Carlton

et al. we see that B4% of the particle mass released by

ships consist of black carbon. Using the same instru-

mentation and sampling strategies as in the present

study, Sinha et al. (2003) derived black carbon and TPM

emission factors for savanna fires in southern Africa of

0.3970.19 and 10.077.5 g kg�1 of fuel, respectively. As

was the case for ship exhausts,B4% of the particle mass

released by African savanna fires consisted of black

carbon.

5.3.7. Particles

Emission factors for three classes of particles are given

in Table 2: total number of particles with diameters

>0.003mm (CN), number of particles with diameters

from 0.1 to 3mm (CN0.1–3 mm), and number of cloud

condensation nuclei (CCN) at 0.3% supersaturation.

Emission factors from ships of CN0.1–3 mm and CCN

have not been reported previously.

Hobbs et al. (2000) found that the CN emission factor

for ships burning residual fuel ((1.670.5)� 1016 parti-

cles per kilogram of fuel) is higher, on average, than for

ships burning distillate fuel ((0.4–1.3)� 1016 particles per

kilogram of fuel). This is consistent with our measure-

ments on the Royal Sphere and MSC Giovanna (Table

2). The higher emission factors for CN reported here

((4–6.2)� 1016 particles per kilogram of fuel) than by

Hobbs et al. is consistent with the fact that our CN

measurements were made with a TSI 3025A ultrafine

condensation particle counter with a diameter range of

0.003–3mm, whereas, the CN measurements of Hobbs

et al. were made with a TSI 3760 condensation particle

counter with a diameter range of 0.011–3 mm.Shown in Fig. 2b are particle size distributions

measured in the plumes from the Royal Sphere, the

MSC Giovanna, and in the ambient marine air. The

number concentration of particles with diameters of

B0.1mm was over three orders of magnitude greater in

the plumes of the ships than in the ambient marine air.

The particle diameter mode of the effluents from the

diesel-powered Royal Sphere burning distillate fuel was

0.10mm and for the diesel-powered MSC Giovanna

burning residual fuel it was 0.12mm. Hobbs et al. (2000)measured a particle mode diameter of 0.04 mm in the

plume from a steam-turbine powered ship burning

distillate fuel and particle mode diameter from 0.06 to

0.1mm for diesel-powered ship burning residual fuel.

The ratios of CCN (at 0.3% supersaturation) to CN

for the Royal Sphere and MSC Giovanna are 19% and

18%, respectively. Hobbs et al. (2000) obtained a CCN/

CN ratio of 1877% for a ship burning residual fuel by

measuring DNd=DNtot; where DNd is the increase (above

ambient) in cloud drop concentrations in the ship track

and DNtot the sum of the increases (above ambient) of

cloud droplet and cloud interstitial aerosol concentra-

tions in the ship track. The CCN can nucleate cloud

droplets, and thereby increase the reflection of solar

radiation by clouds (Hobbs et al., 2000).

The SO2 and NOx emitted by ships may react

heterogeneously on particles to form SO42� and NO3

�.

Most heterogeneous reactions take place on accumula-

tion-mode particles (B0.1–3mm diameter), since these

particles account for most of the surface area of

atmospheric aerosol (Seinfeld and Pandis, 1998). The

CN0.1–3 mm emission factors for the Royal Sphere and

MSC Giovanna reported here (1.1� 1015 and 5.1� 1015

particles per kilogram of fuel, respectively) provide an

estimate of accumulation-mode particle emissions. If it

is assumed that all particles in the accumulation-mode

are spherical and have a diameter of 0.1 mm, the

emission factors for the surface area of these particles

are 34.6 and 160.2m2 kg�1 of fuel burned for the Royal

Sphere and MSC Giovanna, respectively.

6. Global implications

We can estimate the global emissions of various

species from ocean-going ships from the emission factors

given in Table 2 and annual world marine fuel usages of

(100–110)� 109 kg of residual fuel and (30–40)� 109 kg

of non-residual fuel (Corbett et al., 1999). In arriving at

these estimates, we assumed (based on the justifications

given above) that the MSC Giovanna was burning

residual fuel and the Royal Sphere was burning distillate

fuel when we sampled their plumes. The results are

shown in Table 3.

Our estimates of global emissions can be compared

with those of Corbett et al. (1999) for CO2, NOx, and

SO2 (Table 3). In view of the inherent uncertainties of

the estimates, the global emissions of CO2 and NOx (as

N) obtained in this study (97–124 and 3.3–4.2 Tg yr–1,

respectively) are not significantly different from those

obtained by Corbett et al. (123 and 2.66–4.00 Tg yr–1,

respectively). However, the annual flux of SO2 from

ships estimated by us (B2.5 Tg S yr�1) is significantly

lower than Corbett et al.’s estimate of 4.24Tg S yr�1.

However, since the sulfur fraction of the distillate fuel

(B0.1%) burned by the Royal Sphere, which is implied

by our SO2 emission factor for the Royal Sphere, is well

below the maximum legal sulfur content of distillate

fuels (2%) specified by IOS (1987), our estimate of

global SO2 emissions from ships is likely an under-

estimate.

P. Sinha et al. / Atmospheric Environment 37 (2003) 2139–21482146

Emissions from ocean-going ships are compared with

those from some other anthropogenic sources and from

natural sources in Table 3. Two major anthropogenic

emission sources are fossil fuel combustion and biomass

burning; major natural sources include the oceans and

vegetation. For several of the species measured in this

study (e.g., CO2, CO, CH4), emissions from ships are

minor compared to fossil fuel combustion. However, since

ship emissions occur primarily over relatively unpolluted

oceanic regions, they may have significant local and

regional impacts, particularly in the Southern Hemisphere.

In the case of NOx and SO2, ocean-going ships

constitute a globally important emission source: they

emit B10–14% of the NOx emissions from fossil fuel

combustion and B3–4% of SO2 emissions from fossil

fuel combustion. Ship emissions of NOx are B40% of

those from biomass burning, and emissions of SO2 from

ships are B70% of those from biomass burning. Using

Carlton et al.’s (1995) emission factor for NOx (which is

in reasonable agreement with our measurements—see

Table 2), Lawrence and Crutzen (1999) concluded that

emissions from ships produce NOx enhancements of

more than 100-fold in busy ship lanes, and by more than

a factor of two over most of the North Atlantic, North

Pacific, and Indian Oceans. Kasibhatla et al. (2000)

reassessed the effects of ship emissions on NOx

concentrations in the marine boundary layer using

Carlton et al.’s emission factor but updated information

on ship positions. The impact of ships on NOx were

found to be more widespread, but the peak enhance-

ments less than those suggested by Lawrence and

Crutzen. However, Kasibhatla’s model-simulated con-

centrations of NOx over the central Atlantic Ocean were

much greater than in situ measurements. The reason for

this discrepancy is unclear.

We have reported here the first measurements of

emissions of black carbon, CN0.1–3 mm, and CCN (at

0.3% supersaturation) from ships. The black carbon

emissions from ships (B0.02 Tg yr�1) are small in

relation to both fossil fuel combustion (B6–8Tg yr�1)

and biomass burning (B4.8Tg yr�1). However, since

there are no oceanic sources of black carbon, emissions

of black carbon from ships could be important in direct

radiative forcing over the oceans. Also, particle emis-

sions from ships can affect cloud structures and cloud

radiative properties over major shipping lanes (Hobbs

et al., 2000).

Acknowledgements

We thank all members of the UW-CARG and the

pilots of the Convair-580 for help in obtaining

measurements, Dan Jaffe for help in calibrating the

gas instruments, Donald Blake for analyses of the GC/C

samples, and Richard Gasparovic for help in the

identification of ships.

This study was carried out as part of the SAFARI

2000 Southern African Regional Science Initiative.

Research supported by grants NAG5-9022 and

NAG5-7675 from NASA’s Radiation Science Program,

and grants ATM-9901624 and ATM-9900494 from

NSF’s Division of Atmospheric Sciences.

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Global emissions from ocean-going ships compared with some other anthropogenic sources and natural sources. Units are Tg yr–1

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CO 0.76–1.06 650 690 50 150

CH4 0.37–0.47 75–110 39 10–15 115–237

NMHC 0.09–0.14 49

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