The characterization of ultrafine particle emissions from jet aircraft
equipped with turbofan engines, which are commonly used in civil aviation, is an important issue in the assessment of the impacts of aviation on climate and human health. We conducted field observations of aerosols and carbon dioxide (
Civil aviation has grown rapidly as a result of global economic development.
Consequently, the impacts of aircraft emissions on climate and human health
have been recognized as an important issue (ICAO, 2017; Masiol and Harrison,
2014; Stacey, 2019; and references therein). The characterization of ultrafine
particles (UFPs; diameters of
The primary importance of aviation-produced aerosol particles in assessing the
climate impacts is the formation of contrail cirrus clouds from soot or black
carbon (BC) emitted at aircraft cruising altitudes (Kärcher and Voigt,
2017; Kärcher, 2018). Furthermore, aircraft emissions can significantly
affect the number concentrations of Aitken mode particles in the upper
troposphere (Wang et al., 2000; Lee et al., 2010; Righi et al., 2013,
2016). Righi et al. (2013, 2016) showed that the impacts of aviation on
aerosols were sensitive to the parameterization of nucleation-mode particles
(
The health impacts of UFPs, although they are not specific to aircraft
emissions, have been extensively studied by many researchers (Oberdörster
et al. (2005), Ohlwein et al. (2019), and references therein). UFPs can be
efficiently deposited in the nasal, tracheobronchial, and alveolar regions in
the human respiratory system, and the uptake and translocation (physical
clearance) of solid UFPs such as soot into the blood and lymph circulation
could be an important pathway (Oberdörster et al.,
2005). Sub-10
A number of experiments have been performed at engine-test facilities and
under real-world conditions to investigate gaseous and particulate emissions
from aircraft equipped with turbofan engines, which are commonly used in civil
aviation (e.g., Hagen et al., 1998; Petzold et al., 1999, 2005; Kärcher
et al., 2000; Brock et al., 2000; Herndon et al., 2008; Westerdahl et al.,
2008; Onasch et al., 2009; Kinsey, 2009; Timko et al., 2010, 2013; Lobo
et al., 2015a, b; Moore et al., 2017a, b; Kinsey et al., 2019; Yu
et al., 2017, 2019; Durdina et al., 2019). The key findings from the previous
studies include the following two points. First, significant formation and
evolution of volatile particles with diameters smaller than 10
Alongside these scientific studies, the International Civil Aviation
Organization (ICAO) has authorized a new regulatory standard for the mass
and number emissions of particles emitted from aircraft engines (ICAO,
2017). In the method for measuring non-volatile particle number
concentrations described in the Aerospace Recommended Practice (ARP) 6320,
issued by the Society of Automotive Engineers (SAE-ARP6320) (SAE, 2018), the
number concentrations of aerosol particles with diameters larger than 10
Direct measurements of UFPs behind jet engines (either in engine test cells or
aircraft hangers) can provide systematic emission data as a function of the
engine thrust and fuel types from selected jet engines under well-controlled
conditions. A common issue in measuring UFPs behind jet engines in the
previous scientific studies and in the regulatory standard is the significant
loss of particles in long sampling tubes and/or the VPR when fresh aircraft
exhaust plumes are sampled (Kinsey, 2009; Lobo et al., 2015a, b; Durdina
et al., 2019). Although corrections for particle loss have been extensively
evaluated and carefully considered for quantifying particle number
concentrations, the absolute values of the correction factors and relative
errors associated with the corrections tend to be larger for smaller particles
(Kinsey, 2009; Lobo et al., 2015a, b; Durdina et al., 2019). Furthermore, the
large uncertainty in measuring the particle number size distributions for
diameters smaller than 20
Field measurements of advected (diluted) aircraft exhaust plumes near runways are not optimal for obtaining systematic emission data, whereas potential artifacts associated with long sampling lines and/or high concentrations of condensable materials can be reduced by this approach. Furthermore, a variety of exhaust plumes from different types of in-use aircraft engines can be collectively characterized by field measurements near runways. Considering that the accessibility to platforms for sampling fresh engine exhausts (engine test cells, aircraft hangers, and runways) is generally restricted, these approaches should be complementarily selected for better characterizing UFP emissions from aircraft. Consistent integration of the data is also important for constructing reliable emission inventories from the aviation sectors for the global troposphere (cruising altitudes), where the accessibility to sampling platforms is extremely limited.
We conducted field measurements of UFPs near a runway at Narita International
Airport (NRT), Japan. We used multiple instruments for the measurements of
particle number concentrations and size distributions and carefully
investigated the performance and consistency of these instruments. The
purpose of the present study was to investigate the emission characteristics
of sub-10
The field measurements were performed using two containers placed at an
observation point
Approximate layout of Narita International Airport (NRT). The
observation point was located
Figure 2a illustrates a schematic diagram of the sampling setup for the UCPC,
CPC, SMPS, and
As mentioned earlier, the measurements of particles below 20
The EEPS was operated independently from the UCPC–CPC–SMPS inlet system
(Fig. 2b), and it measured the unheated particle number size distributions
during the entire period. The sample flow rate of the EEPS was
10
The
The
The overall penetration efficiencies of particles through the sampling tubes
were estimated by using the theoretical formulae proposed by Gormley and
Kennedy (1949). Details of the calculation procedures are given in Sect. S1
of the Supplement. The penetration efficiency for the UCPC and CPC sampling
line (unheated mode; from the top of the inlet to the flow splitter) was
estimated to be 70 %, 87 %, and 94 % for particle diameters of 5,
10, and 20
The particle diffusion loss during sampling is an important issue for the
quantification of UFPs, as mentioned in Sect. 1. The corrections for the
penetration efficiencies through the sampling tubes and the detection
efficiencies (see Sect. 3.1 for details) were not incorporated in the UCPC and
CPC data presented in Sect. 3.2.1–3.2.4 because the actual size
distributions in the sub-10
Potential artifacts due to the nucleation of gaseous compounds vaporized from
particles in the evaporation tube (hereafter referred to as nucleation
artifacts) were evaluated. Predicting the nucleation rates requires an
estimate of the supersaturation of nucleating compounds, which is highly
uncertain. Here we evaluate the growth rate of nucleated clusters under the
given condition. The upper limit of this effect can be estimated by assuming
that the number concentration of the vaporized compounds remains constant
after a certain period of time (
Let us assume a condensable material (number concentration of molecules:
Other potential artifacts may originate from the condensational growth of
non-volatile particles (or residual particles downstream of the evaporation
tube) smaller than the detectable size range of the UCPC (diameter
The accuracy of the measurements of particle number concentrations was the key issue in this study and thus was evaluated in the laboratory at AIST before and after the field measurements. We mainly used the data obtained after the field measurements because they were more comprehensive than those obtained before the measurements. The test items included the size-resolved detection efficiencies of the UCPC and CPC, the penetration efficiency of non-volatile particles through the dilution–heater section, and the removal efficiency of volatile compounds through the evaporation tube.
An electrospray aerosol generator (EAG; model 3480, TSI), a combustion aerosol
standard (CAST; Matter Engineering, AG, Wohlen, Switzerland) with a tube
furnace for thermal treatment at 350
The experimental apparatus for measuring the size-resolved detection
efficiencies of the UCPC and CPC was similar to that used in our previous
studies (Takegawa and Sakurai, 2011; Takegawa et al., 2017), except that the
sampling line was longer for the CPC. The length of the sampling line for the
CPC was
We also tested the removal efficiencies of tetracontane particles for
diameters of 30 and 50
Figure 3a shows the size-resolved detection efficiencies of the UCPC and CPC measured at AIST. The detection efficiencies for the UCPC and CPC were empirically estimated by using our previous calibration results for the CPC (Takegawa and Sakurai, 2011), the manufacturer specifications for the UCPC (Takegawa et al., 2017), and the penetration efficiencies in the instrument (for the UCPC; Wimmer et al., 2013) and the sampling lines. The penetration efficiencies were calculated by using the theoretical formulae proposed by Gormley and Kennedy (1949). Further details of the empirically estimated detection efficiencies are given in Sect. S1 in the Supplement. We found a good agreement between the experimental data and the estimated detection efficiencies for both the UCPC and CPC.
Laboratory evaluation of the performance of the UCPC and CPC.
Figure 3b shows the penetration and detection efficiencies of non-volatile
soot particles through the 350
Time series of
The SAE-ARP6320 protocol specifies that the removal efficiencies of
tetracontane particles in a VPR should be higher than 99.9 % for particle
diameters of 15 and 30
Remaining fraction (%) of tetracontane (
Figure 4 shows time series of
Figure 5a is a scatterplot of 1
Figure 6 shows time series of total particle number concentrations measured by
the CPC and EEPS and the particle number and volume size distributions
(
In the enhancement events at 14:10 and 14:20
Figure 7 shows the particle number and volume size distributions measured
simultaneously by the EEPS and the 350
The effects of nucleation artifacts (Sect. 2.2) might be a major concern but
were likely small under the observation conditions because the mass
concentrations of aerosol particles in the aircraft plumes inferred from
Fig. 7 were much lower than the threshold concentration (50
The temporal variations in aerosol particles and number size distributions of aerosol particles clearly indicate that the observed air parcels were significantly affected by aircraft emissions under appropriate wind conditions. However, aircraft emissions from various cycles of take-off, landing, and idling may have been mixed in the atmosphere. We calculated the enhancements of
Particle number emission indices (EIs) (particles per kilogram of fuel)
and sub-10
Note: The particle number EI values for unheated
The
The median total and non-volatile EI(
Previous studies have shown that the particle number EIs can vary significantly depending on the engine type, the engine thrust, the fuel sulfur content, the plume age, and the ambient conditions (Petzold et al., 1999, 2005; Kärcher et al., 2000; Brock et al., 2000; Onasch et al., 2009; Timko et al., 2010). The sampling setup (deployed instruments and sampling location relative to the runways) and the analysis procedures (discrete plume analysis) of this study are similar to those of Lobo et al. (2012, 2015b) and Moore et al. (2017a). Therefore, it is worth discussing the similarities and differences between those studies and our results. The fuel sulfur content is an important parameter for the comparison with other studies. We do not have information on the sulfur content of the fuel that was actually used at NRT. Instead, we analyzed fuel samples (Jet A-1) provided by a jet fuel company in Tokyo (Ishinokoyu, Co. Ltd.) (Saitoh et al., 2019b). We obtained a total of five samples between August 2017 and August 2018. The sulfur content of the fuel samples ranged from 30.4 to 440 ppmw (parts per million by weight). We assume that these values are representative of the sulfur content of jet fuels commercially available in Tokyo during the observation period.
Lobo et al. (2012) reported particle number and mass EIs measured
100–350
Lobo et al. (2015b) reported the particle number and mass EIs measured near
the jet engine exits and 100–350
Moore et al. (2017a) reported the particle number and volume EIs for take-off
plumes measured 400
Timko (2010) showed that the total particle number EIs in moderately diluted
plumes (measured by a CPC 3022A), which were dominated by volatile particles,
exhibited a relatively weak dependence on the fuel sulfur content (
The enhancements of
Size distributions of
The total and non-volatile particle number EIs derived from the UCPC and CPC
fell in the same range as those from the previous studies for take-off plumes
under real-world operating conditions (Lobo et al., 2012, 2015b; Moore et al.,
2017a), as described in Sect. 3.2.4. However, the characteristics of the size
distributions appeared to be significantly different. The mode diameters of
the
The uncertainties in the
We estimated the possible particle number size distributions for the total
and the non-volatile particles constrained by the UCPC and CPC observations
and investigated the consistency with the EEPS and SMPS measurements. We
assumed lognormal number size distributions with various geometric mean
diameters (GMDs) and geometric standard deviations (GSDs). We calculated the
number fraction of sub-10
Figure 9 shows the calculation results for the total particles. GMD values of
Figure 10 shows the calculation results for the non-volatile particles.
Similarly to the total particles, GMD values of
The characteristics of the total particles observed in this study are
qualitatively consistent with the findings from previous studies (e.g.,
Petzold et al., 1999, 2005; Lobo et al., 2012, 2015b;
Kärcher et al., 2000; Brock et al., 2000): i.e., the total particle number
EIs are dominated by volatile particles, and the sub-10
An alternative possibility for the significance of sub-10
The key point in our results is that the non-volatile particle number and
volume EIs originating from soot-mode particles (
Our results have an implication for jet engine exhaust measurements by the
SAE-ARP6320 method. The non-volatile
Our results also have an implication for the emission inventories of the
aviation sector. Although the potential contributions of sub-10
We conducted field measurements of aerosols at an observation point The median values of the total and the non-volatile EI( More than half the total and the non-volatile particle number EIs in the aircraft take-off plumes were found in the size range smaller than 10 The unheated UCPC, CPC, and EEPS data consistently suggest that the mode diameters of the The EEPS data suggest that the non-volatile particle number and volume EIs originating from soot-mode particles (
The characteristics of particle emissions may significantly depend on the type of jet engine, the maintenance conditions, and the fuel sulfur content, which are not available in this study. Particle emissions may also depend on other factors including ambient pressure and temperature. These factors should be carefully considered for a more systematic comparison of different studies.
The field measurement data used in this study are available at the Zenodo data repository (
The supplement related to this article is available online at:
NT, AF, and HS designed the research; NT, AF, KM, YF, and KS performed field observations and collected data; NT, YM, and HS performed laboratory experiments; NT and YM performed data analysis; NT, AF, YF, and HS wrote the paper.
The authors declare that they have no conflict of interest.
We thank Narita International Airport Corporation and Narita International Airport Promotion Foundation for their help during the field observations at Narita International Airport. We also thank Takumi Saotome at the Research Institute for Environmental Strategies, Inc., Makiko Mine and Anna Nagasaki at Tokyo Metropolitan University for their help in the observations and data analysis, and Kenjiro Iida at AIST for useful advice on the evaluation of the UCPC and CPC.
This research has been supported by the Ministry of the Environment, Japan (grant no. Environment Research and Technology Development Fund (5-1709)).
This paper was edited by Andreas Petzold and reviewed by two anonymous referees.