Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is well-drafted, with a comprehensive introduction that includes the background of the study, literature review, objectives, and significance. Methodology and result are justified to the research work. However, I suggest adding a few sentences to highlight the relevance of the study in the current context. Additionally, some sections require citations, and a few grammatical and language errors have been noticed. Specific corrections and suggestions are provided in the attached document.
Comments for author File: 
Comments.pdf
Author Response
Comments 1: I reviewed the manuscript titled "Concentrations and Source Apportionment of Tetrachloroethylene (PCE) in Aircraft Cabins" carefully. I found several mistakes that should be corrected by the authors. Line 53: write full name of NIOSH and ACGIH.
Response 1: Thank you for pointing this out. We have added full names as follows: “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.” (Page 2, Paragraph 1, Line 53-55)
Comments 2: Line 59: “Indoor” I should be in lowercase.
Response 2: Thank you for pointing out this problem. We have revised “In China, PCE has been included into the revised indoor air quality standard (GB/T 18883-2022).” (Page 2, Paragraph 1, Line 61)
Comments 3: What is NHC and PRC in row 8 of table 1.
Response 3: We are sorry for our carelessness. We have corrected “NHC and PRC” into “SAMR (PRC), SAC” in Table 1, and explained “SAMR (PRC) is the State Administration for Market Regulation of the People's Republic of China. SAC is the Standardization Administration of the People's Republic of China” in footnote of Table 1. (Page 3, Paragraph 1, Line 65-66)
Comments 4: Line 194-203: Cite all the research article which has been compared.
Response 4: Thank you for your constructive suggestion. There are only PCE concentrations in aircraft cabins of this study and a published residence study (including eight cities conducted by the same group, reference [38]) for comparison. Because for other aircraft cabin studies listed in Table 2, there may be different quantification method for PCE.
For clearer expression, we have revised as follows: “To further explore the difference of PCE concentration distribution between aircraft cabins and building indoor environment, the PCE in aircraft cabins of this study and PCE in residences from a previous study by the same group were compared [38], as shown in Figure 3. The previous residence study included 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 con-centration 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 cabin (red bar).” (Page 6, Paragraph 3, Line 203-206)
Comments 5: Line 209 & 210: Citation needed.
Response 5: Thank you for your constructive suggestion. We have added seven citations in revised manuscript “PMF model was applied to identify sources and estimate quantitative source contributions to cabin PCE [36]. According to published literature related to pollutant emission [32, 61, 71, 74, 31, 88]”. (Page 7, Paragraph 2, Line 218-219)
Comments 6: Line 270: what is DOP, DINP. Mention full name.
Response 6: We agree with the comment. We have added the full names as follows: “Especially for wet PVC carpet, because of hydrolysis reactions with plasticizers of di-octyl-phthalate (DOP), di-isononyl phthalate (DINP), widely added in polymer ma-terials like PVC carpets, 2E1H was treated as the second biggest emission product by degradation of polymer materials or PVC additives.” (Page 9, Paragraph 1, Line 280)
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper deals with the air emissions of tetrachloroethylene (PCE) on board aircraft. In the paper, the authors discuss the influence of the phase of flight , the effect of the aircraft deck equipment and the effect of the cleaning agents used during aircraft cleaning on the amount of PCE emissions. The conclusions of these measurements summarized in the conclusion are very interesting. However, the paper lacks information on the aircraft occupancy ( number of people) the ambient temperature which has an effect on the amount of emissions and the humidity of the environment during the measurement. I also recommend to mention the air pumping rate through the sampling tubes.
It is advisable to include units and numbers on one line, see line 16.
Author Response
Comments 1: the paper lacks information on the aircraft occupancy (number of people) the ambient temperature which has an effect on the amount of emissions and the humidity of the environment during the measurement.
Response 1: Thank you for your constructive suggestion. We have added indoor parameters such as temperature and humidity in revised manuscript: “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 described in a previous study [37].” (Page 3, Paragraph 4, Line 91-94). Due to a lack of passenger number recording, we could not afford to provide occupancy information. But we would improve sample methods in the future to assure accurate passenger information.
Comments 2: I also recommend to mention the air pumping rate through the sampling tubes.
Response 2: Thank you for pointing this out. The pumping rate could be found in section 2.1: “Tenax-TA adsorption tubes (0.20 mg adsorbent, 60–80 mesh, Markes, UK) with a portable pump (BUCK-Libra Plus Model LP-1, A.P. BUCK Inc., USA) at a flow rate of 0.2 L/min for 20 min.” (Page 3, Paragraph 4, Line 101-103)
Comments 3: It is advisable to include units and numbers on one line, see line 16.
Response 3: Thank you for your careful comment. We have checked the whole manuscript, and make sure all numbers and units are in the correct format. (Page 1, Paragraph 3, Line 16), (Page 4, Paragraph 1, Line 113)
Reviewer 3 Report
Comments and Suggestions for AuthorsThis article reports on the analysis of tetrachloroethylene in aircraft. This article is expected to contribute to the development of the field.
Some comments are made as follows.
There is no diagram showing what analytical methods and equipment were used. Please insert such a diagram to help the reader understand.
Among the alkyl chlorides, why did you focus on tetrachloroethylene in this case? Can alkyl chloride of lower molecular weight also be analyzed using this technique?
You have included the results by aircraft type in Figure 1. Don't these results vary greatly from airline to airline?
The discussion in 3.22 and 3.2.5 is difficult to understand due to the text alone. Please use graphs, etc. as appropriate.
It is well written and worthy of acceptance if the sections I commented on to the author can be corrected.
Author Response
Comments 1: There is no diagram showing what analytical methods and equipment were used. Please insert such a diagram to help the reader understand.
Response 1: Thank you for your constructive suggestion. We have added the figure 1. (Page 4, Paragraph 1, Line 116-117)
Figure 1. The process of on-flight sampling (T/RH/VOCs)
Comments 2: Among the alkyl chlorides, why did you focus on tetrachloroethylene in this case? Can alkyl chloride of lower molecular weight also be analyzed using this technique?
Response 2: Thank you for pointing this out. There are three main reasons for focusing PCE as cabin target VOC: (1) PCE showed high detection rates of 57%-90% in aircraft cabins in published studies, while the rate was lower of 30% in residences. In another word, PCE may be a particular pollutant in aircraft. (2) PCE has adverse health impact, even short-term exposure may cause physical discomfort such as headache, dizziness and forgetfulness. (3) Standard for indoor air quality in China has included PCE as target VOC in residence, which means PCE would gradually become a noteworthy VOC in other indoor environments like cabins.
For other chloride VOCs such as trichloromethane, trichloroethylene and tetrachloromethane (lower molecular weight) could also be sampled by Tenax-TA tubes with pump, and analyzed by TD-GC/MS, as referenced by the Standards for Indoor Air Quality (GB 18883-2022).
Comments 3: You have included the results by aircraft type in Figure 1. Don't these results vary greatly from airline to airline?
Response 3: Thank you for your careful comment. We agreed with that there is difference in PCE distribution between different airlines and flights. And we also found that there is difference in the same airline. Indeed, according PMF source apportionment, cleaning products may account for the largest PCE source contribution. As a result, the usage of cleaning products may be the basic cause of PCE difference between airlines, flights, or aircraft type.
Comments 4: The discussion in 3.22 and 3.2.5 is difficult to understand due to the text alone. Please use graphs, etc. as appropriate.
Response 4: Thank you for your constructive suggestion, and we appreciate it. In 3.2.2, we discussed the “Factor 2: Aircraft Cleaning/Maintenance”, and the corresponding graph is as illustrated in figure 5.
The first paragraph of “Factor 2 had high percentage of p-xylene (92.1%)…” talked about six VOCs had high percentage in Fig.5, which are representative compounds in painting, so, the factor 2 was treated as a source of painting in daily maintenance.
The second paragraph of “Painting is one important phase in aircraft maintenance…” explained the usage of PCE in aircraft painting.
The third paragraph of “PCE is the first characteristic component of solvent-based dry-cleaning agents…” explained PCE was also used as cleaning agents for aircraft outer skin except for outer skin painting. Combined with painting usage, factor 2 was finally identified as a source of Aircraft Cleaning/Maintenance.
In section 2.3.5, we discussed the “Factor 5: Non-fuel Oil”, and the corresponding graph is as illustrated in figure 5.
The first paragraph of “Factor 5 had high percentage of benzene (93.7%)…” talked about five VOCs had high percentage in Fig.5, which are representative compounds in lubricants, so, the factor 5 was treated as a source of non-fuel oil.
The second paragraph of “oil contamination may be introduced by bleeding air into aircraft cabin…” explained the possibility that ventilation system may induce lubricant containing PCE into cabins.
If the explanation is insufficient, we can supply additional graphs or tables as needed.
