Jet engine aircraft are ubiquitous and significant sources of
atmospheric nanoparticles. Using size-resolved particulate samples collected
near a runway of the Narita International Airport, Japan, we clearly
demonstrate that organic compounds in the ambient nanoparticles (diameters:
< 30 nm) were dominated by nearly intact forms of jet engine
lubrication oil. This finding provides direct evidence for the importance of
unburned lubrication oil as a source of aircraft exhaust nanoparticles and
also has an implication for their environmental impacts near airports and in
the upper troposphere.
Introduction
Jet engine aircraft are a significant source of atmospheric nanoparticles and
exist ubiquitously from ground level to the upper troposphere (Masiol and
Harrison, 2014). A new particulate emission standard for turbofan and
turbojet aircraft engines will come into effect from 2020 (International
Civil Aviation Organization, 2017). Therefore, there has been a growing interest in characterizing
aircraft exhaust particles. Previous studies have shown
that the impacts of aircraft on the distribution of nanoparticles in ambient
air may range over a horizontal scale of approximately 16 km near airports
(Hudda et al., 2014). Nanoparticles can penetrate deep into the human
respiratory tract and may have adverse effects on human health (Oberdörster
et al., 2000; Biswas and Wu, 2005). The nanoparticles in diesel vehicle
exhaust emissions are comprised of mainly organic compounds with relatively
high saturation vapor pressures (alkanes, alkenes, etc.), and their lifetimes may be shorter
than those of submicron particles owing to their evaporation and coagulation
(Fushimi et al., 2008; Harrison et al., 2016). To understand the mechanisms
of formation of nanoparticles emitted from jet engines and their
physical and chemical transformation in ambient air, it is important to determine
the size distribution and chemical composition of nanoparticles emitted from
in-use commercial aircraft under real-world conditions.
Previous studies have suggested that aircraft exhaust nanoparticles mainly
comprise volatile particles. For example, the fraction of particles that
completely evaporate below 300 ∘C are approximately 70 %–95 %,
and the number concentrations below 20 nm were found to decrease with an
increasing ambient temperature (Wey et al., 2006). Bulk-level chemical
analyses of aircraft exhaust particles showed that the particle compositions
were dominated by organic compounds under low engine thrust (e.g., idle and
taxi) conditions and elemental carbon under high engine thrust (e.g.,
takeoff and climb) conditions (Agrawal et al., 2008; Presto et al., 2011;
Masiol and Harrison, 2014; Yu et al., 2017). This feature is contradictory to
the volatility of aircraft exhaust nanoparticles. Sulfur compounds
originating from jet fuels are also known to be the major components of
aircraft exhaust particles (Masiol and Harrison, 2014; Yu et al., 2017).
Particle emission factors show a strong dependence on the sulfur
and aromatics contents in jet fuel (Wey et al., 2006; Masiol and Harrison, 2014). On
the other hand, some qualitative markers of jet engine lubrication oil were
commonly found in aircraft exhaust particles (Timko et al., 2010; Yu et al.,
2012). The contribution of lubrication oil to the total organic mass may
range from 5 % to 100 % (Timko et al., 2010; Yu et al., 2012). While such
previous studies have provided useful insights into the characteristics of
aircraft exhaust particles, little is known regarding the origin and detailed
chemical composition of size-resolved particles and especially nanoparticles
(Kinsey, 2009; Presto et al., 2011; Kinsey et al., 2011; Masiol and Harrison,
2014).
The purpose of this study is to determine the size-resolved chemical
composition of particles emitted from jet engine aircraft during takeoff
and landing in real-world conditions, and to estimate the contribution of
jet fuel and lubrication oil to the nanoparticle mass. We have therefore
collected particulate samples from an area near a runway at the Narita
International Airport, Japan, during the daytime and nighttime using
low-pressure cascade impactors. We used thermal desorption–gas
chromatography-mass spectrometry (TD–GC-MS) to identify the chemical
composition of nanoparticles having diameters smaller than approximately 30 nm originating from real-world aircraft emissions, which is unprecedented.
MethodsJet fuels and lubrication oils
To investigate the emission sources of the nanoparticles in aircraft
exhausts, we obtained two Jet A-1 fuels and two jet engine lubrication oils
(Mobil Jet Oil II and Mobil Jet Oil 254, ExxonMobil, Irving, TX, USA) from
Ishinokoyu Co. Ltd. (Mitaka, Tokyo, Japan). The Mobil Jet Oil II has a market
share of 49 % (Winder and Balouet, 2002), and the Mobil Jet Oil 254 is a
newer-generation oil.
Measurement site
Field measurements were conducted at a distance of 140 m west of runway A of
the Narita International Airport, Japan, in winter
(5–26 February 2018, Fig. 1). The instruments used for obtaining the
particle number size distributions and size-resolved particulate samplers
were installed in a container. The airport has two runways. In 2017, the runways A and
B had an average of 401 and 290 flights per day, respectively.
Aircraft operating times are from 06:00 to 23:00. A summary of the
aircraft models used in runway A of Narita International Airport during our
measurement period is given in Table S1 in the Supplement.
Map of the measurement site.
Particle number size distribution
The size distributions of the particle number concentration were measured
every 1 s using the engine exhaust particle sizer (EEPS; model 3090, D=0.006–0.560 µm, TSI, Shoreview, MN, USA; flow rate: 10 L
min-1) during the entire measurement period. A copper tube (inside
diameter: 10 mm, and length: 2 m), electrically conductive tubes (inside
diameter: 6.35 and 9.53 mm; total length: 1 m; part 3001788, TSI), and a
glass manifold (inside diameter: 40 mm; total length: 600 mm) were used to
transport the ambient air at a ground height of 3 m to the EEPS. To avoid
particle deposition onto the sampling tubes and to increase the response
speed, an extra pump (flow rate: 30 L min-1) was used to vacuum the
air inside the glass manifold.
The size distributions of the particle number were also measured every 5 min
using a scanning-mobility particle sizer (SMPS; model 3936, D=15–660 nm, TSI, Shoreview, MN, USA) which consists of an electrostatic
classifier (model 3080), a differential mobility analyzer (DMA; model 3081),
and a condensation particle counter (CPC; model 3022A). Ambient air was
aspirated from the roof of the container through a stainless steel tube
(inner diameter: 10 mm, length: approximately 3 m, inlet height:
approximately 3 m above ground level), and was split into the main sample
flow (approximately 0.8 L min-1) and bypass flow (approximately
20 L min-1). The bypass flow was used to reduce the possible loss of
nanoparticles due to Brownian diffusion. The main sample flow was diluted
with particle-free air (approximately 2 L min-1), and was further split
into the individual sample flows for the SMPS (approximately
0.3 L min-1) and other CPCs (approximately 2.5 L min-1). We
used the dilution flow to reduce the effects of particle coincidence in the
CPCs at higher concentrations. For the SMPS, the penetration efficiency
through the sampling tube was estimated to be > 70 % above
10 nm based on the theoretical formulae of Gormley and Kennedy (1949).
Sampling
Size-resolved particles in the ambient air at a height of approximately 3 m
from the ground were collected using two low-pressure cascade impactors
(NanoMoudi II, model 125B, MSP, Shoreview, MN, USA; flow rate,
10.2 L min-1) simultaneously. To distinguish the effect of aircraft
emissions, the samples were collected during the daytime (during aircraft
operating hours) and nighttime (during non-operating hours). Three daytime
(07:00–22:00) samples were collected from 16:24 on 9 February to 13:09 on
13 February 2018 (duration = 56.8 h, sample no. 1), from 17:33 on
13 February to 09:37 on 17 February 2018 – except for 13:30–16:45 on
15 February 2018 (duration = 48.8 h, sample no. 2) – and from 19 to
20 February 2018 (duration = 30.0 h, sample no. 3). One nighttime
(00:00–6:00) sample was collected during 22–26 February 2018
(duration = 30.0 h, sample no. 4).
For one of the two NanoMoudi II impactors, a gold (Au) foil (diameter:
47 mm, Mitsubishi Materials, Tokyo, Japan; “NanoMoudi II-Au”, hereafter)
was used as the collection substrate for the impaction stage, and a
quartz-fiber filter (diameter: 47 mm, 2500QAT-UP, Pall, East Hills, NY, USA)
was used as the substrate for the backup filter. In the other NanoMoudi II, a
polycarbonate membrane filter (Nuclepore; pore size: 0.05 µm;
diameter: 47 mm; Whatman, GE Healthcare UK Ltd., Buckinghamshire, UK;
“NanoMoudi II-PC”, hereafter) was used as the collection substrate for the
impaction stage. At each impaction stage, a nitrocellulose membrane filter
(AAWP04700, pore size: 0.8 µm; diameter: 47 mm; Merck Millipore,
Billerica, MA, USA) was set underneath the PC filter. A
polytetrafluoroethylene with non-woven fabric polyethylene and polyethylene
terephthalate membrane filter (TFH-47; diameter: 47 mm, Horiba Ltd., Kyoto,
Japan, for samples no. 1 and no. 2) or a quartz-fiber filter (diameter:
47 mm, 2500QAT-UP, Pall, for samples no. 3 and no. 4) was used as the
substrate for the backup filter. The use of different substrates as backup
filters does not alter the flow rates. Using NanoMoudi II, the particles were
separated into 14 size fractions. For the NanoMoudi II-Au, for example, the
equivalent cut-off aerodynamic diameters at a 50 % efficiency (D50) of
the impaction stages, calibrated and reported by the manufacturer, were as
follows: 0.010, 0.018, 0.032, 0.057, 0.105, 0.170, 0.290, 0.560, 1.00, 1.80,
3.10, 6.20, and 9.90 µm. Au foils were rinsed with acetone (dioxin
analytical grade, Wako Pure Chemical Industries, Osaka, Japan) before use. A
copper tube (inside diameter: 10 mm, length: 3 m) was used as the sampling
line. Before each sampling, the impactor nozzles and the support rings of the
NanoMoudi II were cleaned using acetone and blown off with an air duster.
The NanoMoudi II-Au samples were used for particle mass weighing,
elemental and organic carbon (EC and OC) analysis, and organic analysis. The
NanoMoudi II-PC samples were used for elemental analysis. The NanoMoudi II
with aluminum foil as a collection substrate can be used to collect
particles with a reasonable size distribution, and the aluminum foil and PC
filters (on cellulose filters) have comparable collection efficiencies
(Fujitani et al., 2006). Therefore, we assumed that the NanoMoudi II-Au and
NanoMoudi II-PC collected particles with reasonable size distributions, and
their size distributions were comparable with each other. In this paper, the
data for the backup filters are not presented because their collection
characteristics (especially adsorption of gaseous compounds) are remarkably
different from those of the impaction substrates.
Particle mass
The particle masses of NanoMoudi II-Au and NanoMoudi II-PC samples were
determined from the differences between the weights of the collection
substrates before and after the sampling. For the NanoMoudi II-PC samples,
only PC filters were weighed after eliminating static electricity using an
ion balancer (TAS-182 NWM, Trinc Corporation, Shizuoka, Japan). The substrates were
weighed with a microbalance (readability 0.1 µg, UMX2,
Mettler Toledo, Columbus, OH, USA) in a chamber (CHAM-1000, Horiba) in which
the temperature and relative humidity were controlled at 21.5 ∘C and
35 %, respectively. Each sample was weighed twice, and the obtained
results were averaged. If the difference between two recorded weights
exceeded 0.5 µg in the case of the Au samples or 2.0 µg
in the case of the PC samples, the sample was reweighed. The samples were
not conditioned before the weighing because Au foils and PC filters have low
hygroscopicity.
EC and OC
The EC, OC, and total carbon (TC) in the NanoMoudi II-Au samples were
determined by using a thermal–optical carbon analyzer (DRI Model 2001 Carbon
Analyzer; Desert Research Institute, Las Vegas, NV, USA) (Chow et al., 1993).
Three-eighths of each Au-foil sample cut in a fan shape was analyzed after
the outside of the deposit area (diameter: 28 mm) had been cut-off. The
samples were analyzed using the IMPROVE protocol (OC1: 120 ∘C,
OC2: 250 ∘C, OC3: 450 ∘C, OC4:
550 ∘C in a 100 % He atmosphere; EC1: 550 ∘C,
EC2: 700 ∘C, EC3: 800 ∘C in a 2 %
O2/98 % He atmosphere; Chow et al., 2001). The pyrolysis of the
OC during analysis was not corrected because adequate correction using laser
light is not possible with Au-foil samples.
Elements
The elemental compositions of the NanoMoudi II-PC samples were determined
using particle-induced X-ray emission (PIXE) analysis at the Nishina Memorial
Cyclotron Center of the Japan Radioisotope Association in Iwate, Japan. The
target elements were Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Co, Ni, Cu, Zn,
Ga, As, Se, Br, Sr, Y, Zr, Nb, Mo, Hg, and Pb. The NanoMoudi II-PC samples
were mounted on a Mylar target frame and bombarded with 2.9 MeV protons from
a small cyclotron (Sera et al., 1992). The beam current, accumulated charge,
and typical measuring time were 40–60 nA, 20–58 µC, and
10–12 min, respectively. The X-ray spectra thus obtained were analyzed
using the SAPIX program (Sera et al., 1992). A quantitative analysis of the
elemental values was performed using the Nuclepore–Br method (Sera et al.,
1997). Blank filters were analyzed in all the procedures. The accuracy of the
PIXE analysis was confirmed based on the National Institute of Standards and
Technology (NIST) standard reference materials (Saitoh and Sera, 2005).
Time series total number concentrations of particles measured using
the EEPS between 11:00 and 12:00 on 15 February 2018. One second data are shown.
The letters “D” and “A” indicate the departure and arrival times of
aircraft fleets, respectively, reported by Narita International Airport. The
time periods of the “plume” and the “no plume” events, shown in Fig. 3,
are shown here as bars. Wind directions measured at the measurement site are
shown as arrows. The wind speed was 3.2–4.8 m s-1 during this hour.
Organic composition
The organic compounds in the NanoMoudi II-Au samples were analyzed using TD–GC-MS, which is
sensitive and suitable for trace-level particulate samples (Fushimi et al.,
2011). A thermal desorption unit (TDU; Gerstel GmbH & Co. KG, Mülheim
an der Ruhr, Germany), a cooled injection system as a GC inlet (CIS 4;
Gerstel), a 6890 GC (Agilent Technologies, Palo Alto, CA, USA), and a
double-focusing magnetic sector mass spectrometer (JMS-700K, JEOL Ltd., Tokyo,
Japan) were used. For the GC columns, a DB-5MS (length: 30 m, internal
diameter: 0.25 mm, film thickness: 0.25 µm; Agilent Technologies,
Palo Alto, CA, USA) was used.
One-eighth–three-eighths (particulate mass per sample: 1–20 µg) of the NanoMoudi II-Au samples were cut into a fan shape after the outside area (diameter: 28 mm) had been cut off and were placed in a glass
liner (length: 60 mm, outside diameter: 6 mm, inside diameter: 5 mm,
Gerstel). The samples were transferred into the TDU and 1 µL of the
internal standard mixture of 13C-labeled polycyclic aromatic
hydrocarbons (approximately 0.5 µg mL-1 for each compound; US
EPA 16 PAH cocktail, Cambridge Isotope Laboratories, Andover, MA, USA)
and deuterium n-alkane mixtures (10.7 µg mL-1 of
C24D50n-alkane and 11.0 µg mL-1 of
C30D62n-alkane) were injected onto the surface of the samples
using an autosampler (MPS-TEX, Gerstel). The samples were then thermally
desorbed using the TDU; the temperature was increased from 30 ∘C
(held for 0.5 min) to 350 ∘C (held for 3 min) at
50 ∘C min-1, using a helium desorption flow at
50 mL min-1 in splitless mode. The interface temperature was
maintained at 350 ∘C. During desorption at the TDU, the desorbed
compounds were focused at 0 ∘C on a quartz wool inside the glass
liner (inside diameter: 2 mm) in the CIS 4 for subsequent GC-MS analysis.
The CIS 4 was then programmed to increase the temperature from 0 (held for
0.75 min) to 150 ∘C at 960 ∘C min-1 and from 150 to
350 ∘C (held for 3 min) at 720 ∘C min-1 to inject
focused compounds into the GC column. The injection was performed in
splitless mode with a 3 min splitless time. The GC oven was programmed to
increase the temperature from 40 (held for 3 min) to 150 ∘C at
20 ∘C min-1 and to 320 ∘C at
10 ∘C min-1 (held for 15 min). Helium was used as a carrier
gas at 2.5 mL min-1 in a constant flow mode. The temperature of the
transfer line between the GC and MS was 320 ∘C. The samples were
ionized using the electron ionization method (ionizing voltage: 70 V,
ionizing current: 600 µA, ion source temperature: 260 ∘C).
The MS was operated in scan mode (m/z 35–400) with a mass resolution of
1000 to obtain comprehensive information regarding the organic compounds in
the particulate samples. The accelerating voltage was 10.0 kV, and the
detector voltage was 0.40 kV.
Size distributions of particle concentrations with and without
aircraft exhaust plumes. (a) Particle number concentrations.
(b) Estimated particle mass concentrations. The averaging times are
approximately 20 s for both events. The measurement periods were
11:43:42–11:44:01 on 15 February 2018 and 11:43:11–11:43:30 on
15 February 2018 for the “plume” and “no plume” events, respectively, as
indicated in Fig. 2.
The Jet A-1 fuels and the jet lubrication oils were diluted by approximately
1000 times with n-hexane (dioxin analytical grade, Wako Pure Chemical
Industries) and then analyzed with TD–GC-MS under the same condition as the
particulate samples.
Results and discussionParticle number size distribution
In our parallel measurements at the measurement site, the size distribution
and concentrations measured using the EEPS agreed well with those measured
using the SMPS for particles larger than 15 nm. A typical example is shown
in Fig. S1 in the Supplement. However, the EEPS can show an artifact peak at
approximately 10 nm with polydisperse particles, which is not usually
observed in the case of the SMPS (Fujitani et al., 2012). Therefore, we treat
the EEPS data below 10 nm as supporting information and indicate it using
dashed lines in this paper.
Mass concentrations of particles, OC, EC, sulfur, and other elements
by particle size. The data of sulfur and other elements were adjusted so that
the particulate masses of the NanoMoudi II-PC samples at each stage are equal
to that of the NanoMoudi II-Au samples.
From the measurements obtained using the EEPS, total particle number
concentrations remarkably increased up to more than 1×106 particles cm-3 consistently when an aircraft took off or landed
while wind (northerly or easterly winds) was blowing from the runway to the
measurement site (Fig. 2). The peak concentrations of total particle number
(6.8×105–1.3×106 particles cm-3) during the
plume event (indicated in Fig. 2) are approximately 2 orders of magnitude
higher than the baseline concentrations (1.1–1.6×104 particles cm-3) during the no-plume event. Most peaks of
particle number concentrations seem to be attributed to specific takeoffs or
landings of aircraft, judging from the synchronized increase in CO2
(data are not presented in this paper) and the reasonable time delay
(approximately 20–200 s) between aircraft takeoff and landing, and the increase
in particle number concentration. A 1-month time series of total number
concentrations and size distribution of particles is shown in Fig. S2. The
total particle number concentrations during operating hours (06:00–23:00)
were remarkably higher than those during non-operating hours
(23:00–06:00). There was no noticeable enhancement of nanoparticles during
non-operating hours.
Proportions of OC, EC, sulfur, and other elements by particle size.
The peak concentrations of total particle number at our measurement site are higher than the
maximum value (1.5×105 particles cm-3) measured within
3 km of Los Angeles International (LAX) Airport (Hudda et al., 2014). The
result seems reasonable because our measurement site is much closer to the
runway (i.e., 140 m). In fact, Zhu et al. (2011) reported higher total
particle number concentrations (i.e., > 1×107 particles cm-3) during takeoffs at the blast fence of the LAX
airport. The total particle number concentrations at our measurement site is
higher than the average concentrations at a roadside with a large number of
heavy-duty diesel vehicles in Kawasaki, Japan, in winter 2011 (1.2×105 particles cm-3, Fujitani et al., 2012).
Mass chromatograms (m/z 85) of size-resolved ambient particles
collected during the daytime (sample no. 1, 9–13 February 2018) and
nighttime (sample no. 4, 22–26 February 2018) at the Narita International
Airport. Mass chromatograms of Jet Oil II, Jet A-1 fuel, and Au-foil blank are
also shown for comparison. The mass values (in micrograms) presented in the
plots indicate the mass of the samples that were analyzed using TD–GC-MS. The
carbon numbers of n-alkanes are shown in the chromatograms of the
S7 particles and Jet A-1 fuel.
Typical examples of the size distributions of particle number concentrations
measured with the EEPS are shown in Fig. 3a.
When the aircraft exhaust plume approached the measurement site, the modal
diameters were approximately 10 nm or smaller; these values are smaller than
those of diesel vehicle exhaust particles (Fushimi et al., 2011). In
contrast, without the aircraft exhaust plumes, nucleation-mode particles were
not observed. The number size distributions at 40–500 nm with aircraft
exhaust plumes did not show a significant difference as compared to those
without aircraft exhaust plumes. The mass size distributions, as estimated
from the measured concentrations while assuming a density of
1.0 g cm-3, showed significant enhancements in the nucleation mode and
a slight increase in the accumulation mode (Fig. 3b). These results clearly
indicate that nanoparticles of diameters < 30 nm contribute to the
major fraction of aircraft exhaust particle mass.
The size distributions of particle number concentrations averaged during the
sampling periods are shown in Fig. S3a. During the daytime sampling periods,
the modal diameters were approximately 10 nm or smaller. In contrast, during
the nighttime sampling period, the modal diameter was 34 nm, and the peak
concentrations observed (1.1×104 particles cm-3) were lower
than those observed during the daytime (8.8-21×104 particles cm-3) by 1 order of magnitude. These results
clearly show that aircraft emissions greatly affect the atmosphere at our
sampling site during the daytime sampling periods. Although the air was not
necessarily transported from the runway to the measurement site for the
entire daytime sampling periods, remarkable enhancement of nanoparticles was
observed on multiple days during every daytime sampling period. We estimated
the particle mass concentrations from the measured number concentrations
while assuming a density of 1.0 g cm-3 (Fig. S3b, c). At the
nanoparticle size range (stage 11–13), the particle mass concentrations
during the daytime were several times those observed during the nighttime.
This suggests that aircraft emissions also greatly affect the nanoparticle
samples (stage 11–13) during the daytime on mass basis.
Mass chromatograms (m/z 85) of a nanoparticle sample collected
during the daytime (sample no. 1, 9–13 February 2018; S12, diameter: 18–32
nm) at the Narita International Airport, Jet Oil II, and Au-foil blank. The
mass spectra of the peaks at 23.51 min of Narita no. 1–S12 sample and Jet
Oil II with an asterisk are shown in Fig. 8.
Mass spectra of a nanoparticle sample collected during the daytime
at the Narita International Airport (sample no. 1, 9–13 February 2018; S12,
diameter: 18–32 nm) and Jet Oil II at 23.51 min of the TD–GC-MS
chromatograms. The chromatographic peaks are indicated in Fig. 7. The
instrument background spectrum was subtracted for the Narita no. 1–S12
sample.
Particle mass and chemical components
The mass concentrations of the particles, OC, EC, sulfur, and other elements
are shown in Fig. 4 by particle size. Generally, particle mass concentrations
showed bimodal distributions with fine mode (diameter:
0.11–0.56 µm) and coarse mode (1.0–9.9 µm). The
concentrations of the total particle mass were
9.7–13.4 µg m-3 during the daytime and
10.7 µg m-3 during the nighttime. At the nanoparticle stages
(S11–S13, diameter: 10–57 nm), 4–10 µg of the particulate
samples per stage were collected, which was assumed to be sufficient for the
chemical analyses. The size distributions of particle mass concentrations of
NanoMoudi II-AU and NanoMoudi II-PC agreed reasonably with each other.
The OC showed not only a fine mode at 0.11–1.0 µm but also a
nucleation mode at 18–57 nm for the daytime samples no. 1 and no. 2. The
sulfur also showed a bimodal distribution with a nucleation mode at
10–32 nm and a fine mode in all the daytime samples. In contrast, the EC
showed a monomodal distribution with a modal diameter of
0.11–0.56 µm.
In this study, inorganic salts such as nitrate and ammonium were not
measured. Thus, large percentages of the particulate mass remained
unidentified especially in the fine and coarse modes. On the other hand, more than half of the particulate mass is not often explained with the measured OC, EC, ions, and elements even in the case of vehicle exhaust particles,
of which the major components are supposed to be carbonaceous (Fushimi et al., 2011, 2016). Therefore, NanoMoudi II may have a positive artifact on the particulate mass in the nanoparticle size range.
In addition, the particle mass concentration at each stage in the nanoparticle size range was approximately
1.4–10 times those estimated from the number concentrations measured using
the EEPS (Figs. S3c and 4). Therefore, we assumed that the general chemical
characteristics of the nanoparticles can be explained based on the measured
components.
The proportions of OC, EC, sulfur, and other elements are shown in Fig. 5 by
particle size. For the daytime samples no. 1 and no. 2, the EC percentages
were high (up to > 40 %) at approximately
0.057–0.29 µm (stage 8–10). In contrast, the smaller particles in
the nanoparticle size range comprised larger percentages of OC. The OC
proportions were approximately 60 %–80 % in the nanoparticles
(10–32 nm) of the daytime samples no. 1 and no. 2. The sulfur and the sum
of the other elements comprised approximately < 10 % and
10 %–30 %, respectively, in the nanoparticles (10–32 nm) of the
daytime samples no. 1 and no. 2. These results suggest that the nanoparticles
emitted from a wide variety of in-use commercial aircraft with high thrusts
mainly consist of OC. This is interesting and important because there has
been some inconsistency between the volatility of the nanoparticles and the
composition of the bulk particles in previous studies. However, if aircraft
exhaust nanoparticles primarily comprise OC, the higher volatility appears to
be reasonable. The OC proportions can be larger (EC proportions can be
smaller) if the pyrolysis that occurs during the carbon analysis is
corrected. Furthermore, the masses of the organic materials are generally
1.2–3.1 times that of the OC (Bae et al., 2006), and sulfur and other
elements often exist as organic or inorganic compounds. Therefore, the
proportion of organic materials, sulfur compounds, and other elements would be larger than that presented in this paper.
Organic composition of size-resolved particles
A chemical analysis of the size-resolved ambient particles sampled during
daytime suggests that nanoparticles having diameters of 10–32 nm (S12 and
S13 of the impactor stages) are mainly comprised of organic carbon. We thus focus on the chemical characteristics of organic
compounds for this size range, in comparison with those of jet fuels and jet
lubrication oils.
The mass chromatograms (m/z 85) of size-resolved particles collected during
the daytime (07:00–22:00, aircraft operating hours) and nighttime
(00:00–06:00, non-operating hours), jet lubrication oil, and Jet A-1 fuel are
shown in Fig. 6. A series of n-alkanes was detected in the mass
chromatograms (m/z 85, an indicator of hydrocarbons) of Jet A-1 fuels. The carbon numbers of these n-alkanes were in the range of
C11–C18, with the largest peak for C14. Interestingly,
“humps” (baseline elevations) in the mass chromatograms at m/z 85 – which
is often detected in mineral-oil-based lubricants commonly used for
automobiles – were not detected in jet lubrication oils (Mobil Jet Oil II and
Mobil Jet Oil 254). Instead, approximately 25 distinct peaks (likely fatty
acid esters of pentaerythritol) were detected at the retention time of
approximately 21–29 min (corresponding to molecular weights of
approximately 380–530) from two jet lubrication oils (Fig. 6). This is
considered to be reasonable because the base stocks of jet lubrication oils
are essentially a mixture of C5–C10 fatty acid esters of
pentaerythritol (Timko et al., 2010; Yu et al., 2012). Furthermore, three
compound groups (N-phenyl-1-naphthylamine, alkylated diphenyl amines, and
tricresyl phosphate) were detected, which are reported as toxic substances in
the material safety data sheet of lubrication oils. These three compound
groups and fatty acid esters can be used as good markers for jet lubrication
oil or jet exhaust because they are not usually contained in
mineral-oil-based lubricants. In fact, these markers for jet lubrication oil
were not detected from a mineral-oil-based lubricant for diesel vehicles with
our TD–GC-MS analysis. n-Alkanes were not detected from two jet lubrication
oils.
The daytime nanoparticle samples (S13: 10–18, S12: 18–32, and S11:
32–57 nm) clearly show the presence of oil-marker peaks at a retention time
of approximately 21–27 min (likely fatty acid esters of pentaerythritol).
The intensity ratios of these peaks at 22.3 min or later were very similar
to those of a jet lubrication oil (Fig. 7). However, the intensities of the
peaks at 22.3 min, or earlier in the case of the daytime samples, were lower
than those of a jet lubrication oil. This may be due to the partial
evaporation of more volatile compounds in the atmosphere, which was found to
be the case for diesel exhaust nanoparticles in roadside atmospheres (Fushimi
et al., 2008; Harrison et al., 2016). The mass spectra of peaks at 21–27 min from nanoparticles collected during the daytime were very similar
to that of a jet lubrication oil (an example is shown in Fig. 8). In
contrast, the oil-marker peaks from larger particles collected
during the daytime were very small (e.g., S9: 105–170 nm or S7: 290–560 nm) and were not
detected from nanoparticles collected during the nighttime (Fig. 6). The other
marker compounds for jet lubrication oil mentioned above were also detected
in the daytime nanoparticle samples but not in the nighttime samples.
C22–C33n-alkanes were detected in the daytime S9 and S7 samples
but were weak or not detected in nanoparticles.
Conclusions and implications
From the aforementioned results, we conclude that approximately half the
organic compounds in the < 30 nm particles detectable using TD–GC-MS
can be attributed to nearly intact forms of jet lubrication oil. This has not
been identified in previous studies. Jet lubrication oil is released into the
atmosphere through a centrifugal breather vent, located in bypass air flow,
as a droplet smaller than approximately 1 µm or as vapor (Timko et
al., 2010). The vented lubrication oil may be mixed with hot combustion gas
at the exhaust area or in the atmosphere.
Our findings have an important implication for environmental issues from the
ground level to the upper troposphere. The development of superior
technologies for controlling oil emissions (e.g., through a breather vent)
may greatly reduce aircraft exhaust nanoparticles. A reduction in the oil
contributions would be beneficial in mitigating the health risk caused by
aircraft exhaust nanoparticles as jet lubrication oils contain some toxic
materials. Furthermore, a detailed knowledge of aircraft emissions is also
required for improving our understanding of the origin and fate of ambient
particles in the upper troposphere, which can potentially affect the
radiative balance of the atmosphere (Righi et al., 2016).
We believe ambient measurements, such as those described in this paper, can
provide complementary insights into aircraft emissions that are not obtained
from engine exhaust measurements. However, our ambient particulate samples
may have been affected by emissions from a wide variety of jet engines,
operating conditions (e.g., takeoff, landing, taxiing, and idling),
maintenance conditions, and other sources (e.g., auxiliary power units)
(Stettler et al., 2011; Yu et al., 2012; Masiol and Harrison, 2014). The
chemical composition of nanoparticles is also the average of a variety of
emissions, although takeoff and landing seems to have a great impact
because the measurement site is near the runway. These emissions should be
separately evaluated in the future.
Data availability
For the data shown in this paper, please contact the
corresponding author via email (fushimi.akihiro@nies.go.jp).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-19-6389-2019-supplement.
Author contributions
AF contributed to conceptualization, validation, investigation, resources,
data curation, original paper draft preparation, paper review and
editing, visualization, and supervision. KS contributed to conceptualization,
validation, investigation, resources, data curation, and paper review
and editing. YF contributed to validation, investigation, resources, data
curation, and paper review and editing. NT contributed to
conceptualization, validation, investigation, data curation, manuscript
review and editing, supervision, project administration, and funding
acquisition.
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
This work was supported by the Environment Research and Technology
Development Fund (5-1709) of the Ministry of the Environment, Japan. We thank
Narita International Airport Corporation and Narita International Airport
Promotion Foundation for helping with the field measurements at the Narita
International Airport. We also thank Takumi Saotome of the Research Institute
for Environmental Strategies, Inc. for providing the required jet fuel and
lubrication oil; Hiromu Sakurai and Yoshiko Murashima of the National
Institute of Advanced Industrial Science and Technology for evaluating the
performance of the particle number measurements; Koichiro Sera of Iwate
Medical University for his assistance with the PIXE analysis;
Shunji Hashimoto, Teruyo Ieda, Kiyoshi Tanabe, and Yoshikatsu Takazawa of the
National Institute for Environmental Studies (NIES) for their valuable
comments on our TD–GC-MS analysis; Maki Chiba and Masayo Ihara of NIES for
assisting in the filter preparation, weighing, and carbon analysis;
Kentaro Misawa of Tokyo Metropolitan University, Masato Nakamura of Green
Blue Corp., and Hidenori Konno of Horiba Techno Service Ltd. for their
assistance with the sampling; Yutaka Sugaya of NIES for assistance with the
EEPS data analysis; and Ikuo Terabayashi of Aomori Prefecture Quantum Science
Center for his valuable comments on the jet engine mechanism.
Review statement
This paper was edited by Joachim Curtius and reviewed by two
anonymous referees.
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