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Article

Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins

by
Xinyue Dong
1,2,
Yihui Yin
3,4,
Jingjing Pei
2,* and
Meinan Qu
2
1
School of Environment and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
2
Tianjin Key Laboratory of Indoor Air Environmental Quality Control, School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
3
School of Architecture and Urban Planning, Chongqing University, Chongqing 400045, China
4
Key Laboratory of New Technology for Construction of Cities in Mountain Area, Ministry of Education, Chongqing University, Chongqing 400045, China
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(3), 909; https://doi.org/10.3390/su17030909
Submission received: 4 December 2024 / Revised: 27 December 2024 / Accepted: 2 January 2025 / Published: 23 January 2025
(This article belongs to the Special Issue New Insights into Indoor Air Quality in Sustainable Buildings)
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Abstract

:
The aircraft cabin provides a unique indoor environment compared to other building environments. Tetrachloroethylene (PCE) is widely found in cabins and has clear adverse health impacts. This study investigated the PCE pollution characteristics in 56 aircraft cabins using on-flight Tenax-TA tube sampling and GC-MS analysis. PCE was detected at a high rate of 79% in sampled flights, indicating widespread contamination within the cabins. The mean concentration of PCE was 10.12 μg/m3, exceeding the 2.06 μg/m3 observed in residences in a previous study. The positive matrix factorization (PMF) model was used to identify potential sources of PCE in cabins. Six categories of sources were determined, including in-cabin cleaning products, aircraft cleaning/maintenance, cabin interior material, aircraft and vehicle exhaust, non-fuel oil and ozone-associated chemical reactions. The biggest PCE source in cabins was attributed to in-cabin cleaning products (45.30%), followed by cabin interior materials (24.90%), and aircraft cleaning/maintenance (19.82%). The findings of this study are beneficial to improving aircraft cabin air quality, reducing harmful pollutant exposure for cabin crew and passengers.

1. Introduction

As one of the most extensively used modes of transportation, the aircraft cabin environment has been evolving towards sustainability in terms of safety, comfort, and environmental preservation. Different from other indoor environments [1,2,3,4], in such a semi-closed space like that of the aircraft cabin, passengers and crew members may encounter high occupant density, low relative humidity, and air contaminants, such as carbon dioxide, ozone, and volatile organic compounds (VOCs) [5,6,7]. Although the cabin ventilation rate is high [8], 50% of the cabin air flow is recirculated and the other 50% is taken from engine bleeding air, which can bring in pollutants from the ambient atmosphere and engine system. In these cabin contaminants, tetrachloroethylene (PCE) was identified as one of the representative VOCs in aircraft cabins [9]. Prior studies showed high PCE detection rates (57.9–90%) in cabins [10,11,12]. Epidemiological studies indicated that the short-term exposure to PCE can cause physical discomfort, such as headache, dizziness and forgetfulness. The chronic exposure to PCE can decrease an individual’s visual contrast sensitivity, and even adversely affect the central nervous system [13,14,15]. Considering the definite harmful health impact and its high detection rate, PCE sources in aircraft cabins need to be identified to better control its pollution source and improve cabin air quality. Meanwhile, PCE control helps to limit impacts on individuals and the cabin environment, as well as develop ecologically friendly alternatives, which would be beneficial to balance economic advantages with public health.
PCE is a primary chlorine solvent with broad uses in many fields. As early as in the 1950s, it was notably known as vermicide, degreasing agents and narcotics [16]. In the following years, as a substitute of trichloroethylene, PCE has broad applications in dry cleaning, up to the present day [17,18]. PCE is also commonly used in consumer products and the industry [6,19], which lead to its frequent occurrences in air, water and soil [20]. Based on its known health effects, the International Agency for Research on Cancer (IARC) has classified PCE as a Group 2A carcinogen [21]. It is well recognized that the major exposure path of PCE to humans is through breathing and drinking water [20]; therefore, some safety limits were established to protect people from excessive exposure. For occupational exposure, the Occupational Safety and Health Administration (OSHA) imposed 100 ppm (8 h-time weighted average) as the occupational permissible exposure limit [22]. The National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH) also identified recommendation levels for occupational exposure [23,24]. For indoor environment exposure, the US Environmental Protection Agency (EPA) set 0.04 mg/m3 as the noncancer inhalation reference concentration, based on occupational neurotoxicity studies [25]. The Office of Environmental Health Hazard Assessment (OEHHA), and the Agency for Toxic Substances and Diseases Registry (ATSDR), derived the threshold for acute and chronic exposure, respectively [20,26]. In China, PCE has been included into the revised indoor air quality standard (GB/T 18883-2022) [27]. Table 1 summarizes the specific limits mentioned above. It is noted that 0.04 mg/m3 (0.006 ppm) is a generally accepted threshold for indoor exposure.
No authoritative PCE exposure threshold has been set for aircraft cabin environments. In the limited studies on aircraft cabin pollutants, PCE seems to present a high detection rate and high concentration. In a cabin study, PCE kept at a steady high concentration level of 23 μg/m3 during the meal service, and the concentration fluctuated widely from below the detection limit to hundreds of μg/m3 during the whole flight [29]. An understanding of the levels and sources of PCE in other closed environments would also be helpful. However, most of the closed environment studies focus on VOCs such as carbonyl, PAHs and benzene series, and only very limited information was found for PCE. An investigation of air pollutants in a new car showed a PCE concentration level of 1 μg/m3 [30]. But another measurement indicated that PCE concentrations differed greatly between a new car and one-year-old car [31]. It ranked among the top five compounds (242 μg/m3) in a new car, but not in old cars. For PCE in indoor environments, previous investigations have proven that some household products, including cleaning agents, pesticides and polishes, were the main sources [32,33,34]. Studies on the potential sources of PCE in aircraft cabins were limited. Although a study pointed out that a major source of VOCs during the whole flight was from the cabin interior [35], there was no further analysis about the specific interior source. In a source apportionment study of cabin VOCs, a chemical reaction was identified as the primary source for PCE, which was quite different from the main source of VOCs, i.e., human activity [36]. The comprehensive source profiles of PCE in cabins is still not clear.
This study aimed to investigate the PCE pollution status in aircraft cabins and identify its potential sources in aircraft cabins, as well as the contribution of each source, based on on-flight measurement data.

2. Methodology

2.1. On-Flight Sampling and Analysis

During sampling, the cabin temperature ranged from 21.4 °C to 31.2 °C (median 24.4 °C), and the humidity ranged from 15.0% to 59.0% (median 20.4%). The specific information about indoor environment parameters, such as temperature, humidity and CO2, were sampled by HOBO as described in a previous study [37]. As shown in Figure 1, the measurement of on-flight VOCs (including PCE) was carried out on 56 randomly selected flights, including both domestic and international flights, from May 2018 to June 2019. These flights covered 9 aircraft models (A320, A321, A330, A350, B737, B747, B777, B787, E190), different aircraft ages (ranged from 0 to 20 years), different flight durations (domestic flights 1–4 h, international flights 4–14 h) and 1–5 flight phases (including boarding, take-off, cruising, meal service, and landing). VOCs (including PCE) were actively sampled by Tenax-TA adsorption tubes (0.20 mg adsorbent, 60–80 mesh, Markes, Bridgend, UK) with a portable pump (BUCK-Libra Plus Model LP-1, A.P. BUCK Inc., Orlando, FL, USA) at a flow rate of 0.2 L/min for 20 min. After sampling, all samples were sealed in aluminum foil and stored in a bag refrigerated with ice packs (0 °C) on board, then stored in a fridge (−24 °C) before analysis [37].
Tenax-TA tubes were analyzed by TD-GC/MS (TD-100, Markes, Inc. UK; Agilent 7890B/5975B, Wilmington, DE, USA). For benzene, toluene, p/m-xylene, o-xylene, ethylbenzene, styrene, butyl ester, acetic acid and undecane, the nine compounds were identified from chromatographic retention times using mixed standard solution compounds. External standard methods were separately used to obtain the linear calibration curves of the nine compounds (including 0.02, 0.05, 0.08, 0.1, 0.2, 0.5, and 0.8 μg standards, R2 was higher than 0.98) for quantitative analysis. For the other VOCs (including PCE), the respond factor of toluene was used for their quantitative analysis. The detection limit was about 1 ng for each chemical compound (signal-to-noise ratio, S/N = 3/1). The method detection limit (MDL) was 0.5 μg/m3. More information about the analysis of the VOCs and the analytical conditions of TD-GC/MS can be found in previous studies [37,38].

2.2. Source Identification and Apportionment

Broadly there are generally four source analysis receptor models for the source identification of pollutants in ambient air and soil, namely chemical mass balance (CMB), principal component analysis (PCA), positive matrix factorization (PMF) and Unmix. Compared with other models, PMF is improved based on the PCA model and had constrained factor elements so that the contribution of negative values was not allowed [39,40]. It is applied to situations where the possible source profile is unknown [41], which is the case in aircraft cabins. Therefore, the PMF 5.0, developed by EPA, was used for the PCE source apportionment in this study.
The PMF model used a multilinear engine to decompose the matrix of the original concentration sample data (X) into two matrices: factor contributions (G) and factor profiles (F). Factor residuals (E) were also considered [42].
x i j = ∑ k = 1 p g i k f k j + e i j
where k represents the pollution factors; x i j represents the concentration of compound j in the i sample; g i k represents the amount of mass contribution by factor k to the i sample; f k j represents the compound j’s percentage in factor k; and e i j represents the factor residual of compound j in the i sample.
The PMF defined an objective function Q as shown by Equation (2). The criterion for rational PMF results was to minimize Q. According to the iterative calculation by the least squares method, the original concentration matrix X was continuously decomposed, so that the positive matrices G and F, as well as the minimum value of Q, were obtained.
Q = ∑ i = 1 n ∑ j = 1 m ( e i j / u i j ) 2
where u i j represents the uncertainty of compound j in the i sample.
u i j =                               5 6 × M D L ,   C i j ≤ M D L ( C i j × θ ) 2 + 0.5 × M D L 2 ,   C i j > M D L
where C i j represents the concentration of compound j in the i sample; θ is the error fraction, which was set to 0.1 in this study; and MDL represents the method detection limit, which was set to 1/3 of the minimum of the measured concentration.
More than three hundred VOC species were detected in the measured aircraft cabin, but only 40 species had detection rates higher than 50%. Considering the carcinogenic potential [9] and potential tracer (e.g., butyl ester acetic acid for aircraft painting, octane and nonane for jet fuel/exhaust and hexane for household cleaning products), 12 species with lower detections (2-methyl-1, 3-Butadiene, butyl ester acetic acid, octane, nonane, hexane, acetic acid, 1-butanol, 2-methyl-1-propanol, 2-butanone, 1,4-dichloro-benzene, 1,2-dichloro-ethane, benzothiazole) were also included in the dataset. Therefore, 52 VOCs from 150 on-flight samples were pre-selected for PMF model running.
The initial model running showed that there is an unsteady Q (Qrobust and Qtrue) in base running, indicating that an outlier impacted the Q results. In addition, bootstrap (BS) results showed too many unmapped factors that even the factor number was reduced to 2, indicating a poor repeatable factor or abnormal source affecting the model reliability. Based on a repeat screening, poorly fitted VOC species (too many residuals >±3.0, correlation coefficient <0.1) were set as “bad” and excluded from the model implementation. Finally, 32 species and 6 factors were determined for the final PMF analysis. All of the runs converged and the ratio between Qrobust and Qtrue was less than 1.5. Qexp was calculated as nm − p(n + m) [42], and the ratio of Qrobust and Qexp was between 2.0 and 3.0. Two ratios showed an acceptable fit in the base model running.
The displacement (DISP) and bootstrap (BS) methods were used to evaluate model uncertainty, respectively. The dQ drop was 0.001% (less than 1%) in DISP, indicating that the uncertainty of all the identified factors was in an acceptable range. A total of 100 BS runs with an r2 value of 0.6 showed that there were no unmapped factors and that over 80% of bootstrap factors were mapped to each base factor, indicating a repeatable solution. In summary, 32 VOC species with 6 factors were used in PMF modeling for a steady and robust solution.

3. Results and Analysis

3.1. PCE Concentrations in Aircraft Cabins

In the 56 measured flights, PCE was detected in a total of 44 flights (24 domestic, 20 international), with the detection rate as 79%. In three other studies of aircraft cabin VOC measurement [10,11,12], the detection rate of PCE was 85%, 90%, 57.9%, respectively. Figure 2 shows the mean PCE concentration in the 44 aircraft cabins. For all flights, the mean concentration fluctuated in a range of 0.26–66.77 μg/m3. Among them, the mean concentration on 18 flights was less than 1.0 μg/m3, and that of 11 flights was between 1.0 μg/m3 and 10 μg/m3. The median value of mean concentrations was 1.86 μg/m3, which indicated that PCE concentration was low in most measured flights. However, the highest concentration reached up to 67.77 μg/m3, which may be correlated with cleaning activities, like wearing clothes that were just dry cleaned or the cabin was just cleaned.
Figure 3 shows the PCE concentrations during various flight phases. The median concentration was 1.36 μg/m3, 3.54 μg/m3, 1.49 μg/m3, 4.85 μg/m3, 0.62 μg/m3 for the boarding, take-off, cruising, meal and landing phases, respectively. Considering the media concentration, the PCE concentrations were slightly higher during the take-off and meal phases. One possible reason may be the lower bleed air during the take-off phase. When aircraft accelerate, the bleed air supply power is likely insufficient [8], which may result in the lack of air supply and elevated PCE emission inside cabins. Another possible reason may be related to human activities. Passengers using chlorine-based disinfectants to wipe trays during meal service could emit PCE, as the presence of PCE in some household disinfectants has been proven [32].
Table 2 lists the PCE concentrations in previous aircraft cabin studies [10,11,12,43,44,45,46,47,48]. The median concentrations presented in the literature were in a range of 0.62–2.7 μg/m3, with only one study, by Spengler et al., detecting a much higher concentration of 10.67 μg/m3. For all of the measured concentrations listed in Table 2, most of them were far below the chronic regulation limits set by ATSDR, EPA, OEHHA and WHO (0.006 ppm, 40 μg/m3, 35 μg/m3, 0.25 mg/m3) [20,25,26,28]. Considering the time at which the previous studies were conducted, the PCE concentrations in cabins did not show obvious changes during the last two decades.
To further explore the difference in PCE concentration distribution between aircraft cabins and building indoor environments, the PCE in aircraft cabins of this study and the PCE in residences from a previous study by the same group were compared [38], as shown in Figure 4. The previous residence study included the different geographical locations of cities, sample seasons and ventilation rates, and most of the building indoor concentrations (blue bars) were in the range of 0.75–5.0 μg/m3, with the median concentration of 1.33 μg/m3 in the similar level to the mean concentration of 2.06 μg/m3. This study found a higher mean concentration of 10.12 μg/m3 in aircraft cabins (red bar). The detection rate in aircraft (79.0%) is also higher than that in buildings (9.4–30.0%). The higher PCE and detection rates in cabins suggested that there may be more potential sources of PCE in aircraft.

3.2. PCE Source Identification in Aircraft Cabins

The PMF model was applied to identify the sources of cabin PCE, as well as estimate the quantitative source contributions [36]. According to the published literature related to pollutant emission [31,32,49,50,51,52], six sources were set. When Qrobust/Qtrue was less than 1.5 and Qrobust/Qexp was less than 3.0, a minimum and stable Q was obtained. Finally, six factors—in-cabin cleaning products, aircraft cleaning/ maintenance, cabin interior material, ozone-associated chemical reactions, non-fuel oil, aircraft and vehicle exhaust—were identified as PCE sources in aircraft cabins. The factor profiles given by the PMF model are presented in Figure 5.

3.2.1. Factor 1: In-Cabin Cleaning Products

High percentages of PCE (45.3%), hexanal (49.3%), toluene (20.5%), hexane (41.6%), tridecane (31.3%) and 1,2-dichloroethane (58.5%) were present in Factor 1. Based on the available literature, household cleaning products, deodorizers, and pesticides were important sources of PCE, toluene and hexane [32,53]. The detection rate of PCE among these common household products reached a high of up to 67%. PCE, toluene and hexane are typical components in cleaning products, especially in automotive cleaning, household cleaners and electronic equipment cleaners, where the PCE content could be greater than 20% (w/w) [54]. Tridecane accounted for 3.4% of the emitted products and mainly originates from pesticides [55]. 1,2-dichloroethane is most frequently detected as chlorinated components in bleaches [56]. In a test of bleach-containing products, 1,2-dichloroethane was detected with the second highest concentration [57].
Based on the above analysis, cabin cleaning products were considered to be the biggest contributor of PCE. There may be high residue of PCE remaining in cabins when they are immediately used after cleaning. At the same time, airliners were sometimes required to use repellent spray, which may introduce pesticides residues in cabins. Bleach containing products were often used in aircraft toilets. The wastewater generated in aircraft is known as blue water because of the additive of deodorizer with bleach as the main ingredient [58]. Through a comprehensive consideration of the above discussion, a category of in-cabin cleaning products can be defined as factors contributing to PCE in aircraft cabins, including aircraft cleaning agents, repellents and bleaches (deodorizers).

3.2.2. Factor 2: Aircraft Cleaning/Maintenance

High percentages of p-xylene (92.1%), 2-methylpentane (64.1%), ethyl acetate (57.7%), ethylbenzene (74.5%),1-butanol (67.0%) and butyl acetate (70.3%) are present in Factor 2. P-xylene and ethylbenzene were the most prominent species in this factor. In typical spraying industries, BTEX were the main components of solvents, with the proportion present being more than 80% [59,60]. Oxygen-containing VOCs, like ethyl acetate, also presented a proportion of 20–64% in solvents [61]. Similarly in automobile painting, BTEX were considered as the main tracers, with the largest proportion of 36% in p-xylene [62]. 2-methylpentane was also a major species, with proportion of 2.15% [60]. A field investigation of VOC pollution in an aircraft spraying workshop showed that butyl acetate was the most abundant compound, accounting for 36.3% of the total VOCs, and 1-butanol is one of the top 10 compounds in the finishing process [63].
Painting is an important phase in aircraft maintenance to protect an aircraft from corrosion and increase its lifetime [63]. An Airbus-320 would consume 484 kg of paint per spraying work, which is equal to, approximately, the painting consumption of 200 cars [64]. PCE is used as a vapor-state degreasing solvent in aircraft painting [49]. A survey of solvent use showed a high PCE concentration of 3.55 ppm in the workshop, implying serious PCE pollution generated by painting work [65]. Therefore, in newly painted aircraft, high PCE residuals are very likely to be present.
PCE is the first characteristic component of solvent-based dry-cleaning agents [20]. According to limited references, the basic requirement for aircraft exterior cleaning was that cleansers must be harmless to metal materials, and PCE-based aircraft cleansers could achieve a clean and anti-corrosion result [66]. In addition, the industry standard of Cleaner for Aircraft Components Solvent Type [67] stated that benzene series and PCE are allowed to be used in aircraft components cleaning. The standard of Cleaner for Aircraft Components Cold Tank Type [68] also mentioned that dry cleaning solvents could be added into solvent-based cleaners. Therefore, it is reasonable to identify aircraft components and aircraft exterior cleaning/maintenance as a potential source of PCE in cabins.

3.2.3. Factor 3: Cabin Interior Material

Factor 3 presented high percentages of 2-ethyl-1-hexanol (2E1H) (86.4%), nonanal (50.0%), toluene (43.7%), phenol (83.5%) and hexanal (33.3%). The presence of 2E1H in indoor air was an indicator of carpet emission, and its emission rate from carpets remained almost constant over a period [69], especially for wet PVC carpets, because of the hydrolysis reactions with plasticizers of di-octyl-phthalate (DOP), di-isononyl phthalate (DINP), widely added in polymer materials like PVC carpets. 2E1H was treated as the second most emitted product in the degradation of polymer materials or PVC additives [70]. In the most commonly used adhesive for PVC and linoleum carpets, polyacrylate, the ester linkage would be hydrolyzed to 2E1H when used in humid environments [71]. Toluene, nonanal and hexanal were also commonly emitted VOCs from all test carpets [72,73]. The existence of phenol was due to additives and adhesives in carpet production [50].
As an important interior material in cabins, carpets emitted a mass of VOCs. A test of automobile carpets showed that the concentration of PCE was as high as 92 μg/m3 [50]. In addition, adhesives are one of the common products used in carpets and connect 67% of bonding surfaces in aircraft. PCE was found in commercial adhesives such as epoxy resin [74]. Even in some electric appliances and accessories, like the computer body and the insulation of power cables and switches, PCE was found to be the most detected chlorinated VOC, with a detection rate of 69% [75]. Given the large amount of interior decoration materials, such as carpets, PVC-associated materials and adhesives, they are identified as a potential PCE source in aircraft cabin.

3.2.4. Factor 4: Ozone-Associated Reactions

Factor 4 presented high percentages of 6-methyl-5-Hepten-2-one (6-MHO) (91.2%), decanal (91.5%), heptanal (73.1%) and nonanal (30.8%). 6-MHO, nonanal and decanal are primary products of the ozone reaction with human skin oil and hair [51,76]. Another study also found that 6-MHO was the most commonly detected oxidation product of the ozone reaction with cabin materials and cloth fabric, especially used ones stained with human skin oil [77]. These byproducts were responsible for more than half of the oxidation products in aircraft cabins [78]. Therefore, 6-MHO could be considered as an indicator of the VOCs generated from ozonation.
In aircraft cabins, the ventilation system introduces ambient air into the cabin; therefore, the ozone concentration typically rises to hundreds of ppb at the cruising altitude [77]. Together with the high occupant density in cabins, human-related ozone reactions could generate a series of new volatile byproducts and can be an important source of cabin VOCs.

3.2.5. Factor 5: Non-Fuel Oil

High percentages of benzene (93.7%), eicosane (42.8%), trichloromethane (61.6%), methyl cyclohexane (38.8%), hexadecane (45.0%) were present in Factor 5. In general, benzene and its derivatives are the main components of mineral lubricating oils [79], so it could be considered as a tracer for non-fuel oil, such as lubrication oil [38]. Although there is a lack of information about aircraft lubricants, the information regarding vehicle lubricants indicated that long-chain alkanes (C14–C17) were identified in most grease samples in new cars. This finding supported the presence of hexadecane (C16) from lubricants of seat rails [80]. Another vehicle lubricant study also showed that long-chain alkanes (C18–C25) were predominant in the mineral and base oil [81], supporting the presence of eicosane (C20) in this factor.
Oil contamination may be introduced by bleeding air into aircraft cabins. The bleed air is extracted from engine compressors, which take air from the ambient atmosphere during flight or from the Auxiliary Power Unit when on the ground, and then passes through the air conditioning system and is distributed into cabin [82]. If any leakage of lubricating oil occurred in the ventilation system, the bleed air is easily contaminated. Although there is no direct evidence for the existence of PCE in lubricating oil, the PCE concentration of 2.6 μg/m3 in supply air (with 50% as bleeding air) [31] indicated such a possibility.

3.2.6. Factor 6: Aircraft and Vehicle Exhaust

Factor 6 presented high percentages of dodecane (85.8%), tetradecane (87.8%), naphthalene (85.7%), 2-methylbutane (87.7%), undecane (28.0%) and hexadecane (26.6%). It is obvious that heavy alkanes contributed the most in this factor. Usually, naphthalene, dodecane and undecane are the main VOC constituents in diesel exhaust, while acetone is one of the top three VOCs in gasoline exhaust [83]. Because diesel vehicles produce significant emissions of undecane and dodecane (6–8%), while gasoline vehicles produce negligible emissions of these two compounds, undecane and dodecane were considered as potential tracers of diesel vehicle exhaust [84,85]. In an airport investigation, heavy alkanes (C8-C14, including dodecane, tetradecane, undecane) were treated as tracers to distinguish aircraft diesel fuel exhaust from other fuel exhausts because they accounted for 51–64% of heavy VOCs in aircraft emission [86]. 2-methyl butane, a tracer of gasoline exhaust, was one of the most abundant VOCs in roadside air samples [87].
Except for aircraft landing on ground, there are many other airport vehicles for backup support, such as ground power units, refueling equipment, platforms stairs, shuttles and so on. An identification test indicated the natural existence of PCE in crude oil, and PCE also exists in gasoline, aviation kerosene (jet fuel) and light diesel through the distillation process from crude oil [52]. Another test also showed a PCE concentration of 0.66 mg/L in automobile gasoline and speculated that the presence of PCE was due to chlorine-containing additives in the process of crude oil exploitation [88]. When combusted incompletely, unburned fuel with exhaust could enter cabins through the bleeding air system during flight or through the air conditioning system when landing on ground [89]. In summary, this factor was set as gasoline or diesel exhaust from aircraft or other airport vehicles.

3.3. PCE Source Apportionment

Based on the above six source profiles in aircraft cabins, the contribution apportionment of each factor (source) to PCE were obtained and shown in Figure 6.
It is observed that the biggest contributor of PCE in aircraft cabins was the in-cabin cleaning related source. Nearly 45.30% of PCE was from in-cabin cleaning and the associated products. About 19.82% was derived from aircraft exterior cleaning and maintenance. The following contributions to PCE were cabin interior materials (24.90%), aircraft and vehicle exhaust (9.73%) and non-fuel oil (0.30%). Though ozone-associated chemical reactions were identified as an independent source, its contribution to PCE was very low (<0.05%), as observed from the current model-resolved results.

4. Conclusions

An analysis on the PCE distribution in 56 randomly selected flights was conducted. The PCE detection rates reached up to 79% and was consistent with the findings from prior studies conducted in aircraft cabins. The PCE concentration measured in cabins ranged from 0.26 to 67.77 μg/m3, with a mean value of 10.12 μg/m3. The median concentrations of PCE remained relatively stable during all flight phases. The results of the PMF model showed that the largest source contribution of PCE was attributed to in-cabin cleaning products (45.30%), including cabin clean agents, repellents and bleaches (deodorizers). The remaining source contributions were attributed to aircraft cleaning/maintenance, cabin interior materials, aircraft and vehicle exhaust, non-fuel oil and ozone-associated reactions.

Author Contributions

Conceptualization, J.P.; Methodology, X.D., Y.Y. and M.Q.; Investigation, Y.Y.; Data curation, X.D., Y.Y. and M.Q.; Writing—original draft, X.D.; Writing—review & editing, X.D. and J.P.; Supervision, J.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

This study did not require ethical approval.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The process of on-flight sampling (T/RH/VOCs).
Figure 1. The process of on-flight sampling (T/RH/VOCs).
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Figure 2. Mean concentrations of PCE in 44 aircraft cabins.
Figure 2. Mean concentrations of PCE in 44 aircraft cabins.
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Figure 3. PCE concentrations at different flight phases (μg/m3).
Figure 3. PCE concentrations at different flight phases (μg/m3).
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Figure 4. PCE concentrations and detection rates in aircraft cabins and residences. The bar represents the mean concentration, and the red dot represents the detection rate.
Figure 4. PCE concentrations and detection rates in aircraft cabins and residences. The bar represents the mean concentration, and the red dot represents the detection rate.
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Figure 5. Identified PCE source profile in aircraft cabins by PMF resolved factors.
Figure 5. Identified PCE source profile in aircraft cabins by PMF resolved factors.
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Figure 6. Contributions of different sources to PCE in aircraft cabins.
Figure 6. Contributions of different sources to PCE in aircraft cabins.
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Table 1. Regulations and guidelines applicable to PCE in air.
Table 1. Regulations and guidelines applicable to PCE in air.
No.InstitutionExposure LimitsComments
1OSHA
2013 [22]		PEL: 100 ppmPEL: permissible exposure limit
2NIOSH
2013 [23]		IDLH: 150 ppmIDLH: immediately dangerous to life or health
Potential occupational carcinogen
3ACGIH
2012 [24]		TLV: 25 ppm
STEL: 100 ppm		TLV: threshold limit values
STEL: short-term exposure level
4OEHHA
2019 [26]		AREL: 20 mg/m³
CREL: 0.035 mg/m³		AREL: acute reference exposure level
CREL: chronic reference exposure level
5ATSDR
2019 [20]		Chronic-duration inhalation MRL: 0.006 ppm
Chronic-duration oral MRL:
0.008 mg/kg/day		MRL: minimal risk level
The chronic-duration inhalation MRL was adopted as the acute- and intermediate-duration inhalation MRLs
6EPA
2012 [25]		RfC: 0.04 mg/m3
RfD: 0.006 mg/kg/day		RfC: inhalation reference concentration
RfD: oral reference dose
Carcinogenicity classification: Likely to be carcinogenic in humans by all routes of exposure
7WHO
2010 [28]		Air quality guidelines:
0.25 mg/m3		Annual average
8SAMR (PRC) a, SAC b
2022 [27]		Indoor air quality standard:
0.12 mg/m3		8 h-time weighted average
a SAMR (PRC) is the State Administration for Market Regulation of the People’s Republic of China. b SAC is the Standardization Administration of the People’s Republic of China.
Table 2. PCE concentrations in aircraft cabins of previous studies (μg/m3).
Table 2. PCE concentrations in aircraft cabins of previous studies (μg/m3).
SourceMeanMedianMaxMinSD95th Study Sample
Dumyahn et al., 2000 & Spengler et al., 1997 [44]NANA285NANA27 flights
135 samples
Fox 1997 [45]4.1NA6.62.4NANA2 flights
8 samples
Nagda et al., 2001 [46]5.9NA122.8NANA10 flights
30 samples
MacGregor et al., 2008 [47]NANA5.90NDNANA4 flights
3phases
Crump et al., 2011 [48]0.43ND20.1ND1.041.8>100 flights
981 samples
Spengler et al., 2012 [11]NA0.621.930.05NANAAirline A/B/C
83 flights
NA1.1710.010.07NANA
NA10.67123.01.18NANA
Guan et al., 2014 [10]NA2.8303.9<LODNANA51 flights
3 phases
Wang et al., 2014 [43]2.792.57NANA1.9712.9014 flights
84 samples
Sven Schuchardt 2017 [12]3.8
8.5		1.2
2.7		73.9
42.4		0
0.2		NA14.6
25.1		61 flights
8 flights
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Dong, X.; Yin, Y.; Pei, J.; Qu, M. Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins. Sustainability 2025, 17, 909. https://doi.org/10.3390/su17030909

AMA Style

Dong X, Yin Y, Pei J, Qu M. Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins. Sustainability. 2025; 17(3):909. https://doi.org/10.3390/su17030909

Chicago/Turabian Style

Dong, Xinyue, Yihui Yin, Jingjing Pei, and Meinan Qu. 2025. "Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins" Sustainability 17, no. 3: 909. https://doi.org/10.3390/su17030909

APA Style

Dong, X., Yin, Y., Pei, J., & Qu, M. (2025). Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins. Sustainability, 17(3), 909. https://doi.org/10.3390/su17030909

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