|This study investigated non-polar organic compounds including PAHs, alkanes, hopanes and steranes, by using TD-GC/MS technology, in different size-segregated particles from a city (Jiujiang) in eastern China. While the study did provide some information on the characteristics of organic species in a Chinese city, the manuscript in its present form, in my opinion, needs a further clarification and revision before its suitable for publication. |
Novelty of the study:
Without doubt that it is valuable to investigate the occurrence of tracer organic species in environment to better reflect the scientific understanding on their sources, impacts and roles in air pollution source apportionment, however, it is still a concern in my opinion that the novelty of this study is very limited. The methodologies including sampling, laboratory analysis and data interpretation are not new. Results and most conclusions are as expected and may be limited to the study area and period. So, what makes such a measurement in a local city novel and scientific that desires for the publication in ACP? What’s the implication of this study that is important, may be generated and promote our understanding on the characterization of tracer organics or air pollution? The authors are suggested to rethink about these and add appropriate discussions in the paper before its suitable for publication.
Study site and period:
Why the city is typical in eastern China area? Shall the situation and organic compounds characteristics differ in the studied city from those like Shanghai and Nanjing in east China?
The sampling was from Sep. to Dec. in 2016 (line 102-103), thus this study may be considered as a wintertime study, and results cannot represent a general situation in the city. This info. should be clarified in the title and abstract sections.
NPOC analysis using TD-GC/MS:
Line 142-144, Table 2 may be moved to SI as these parameters are mot key part of the study. I’d like to suggest to a new table listing the retention time and quantification ions for each species in the paper. Though the full scan method has been adopted in the study using TD coupled with GC/MS or MSMS technologies, the accuracy of the quantification is still a big problem. It would be also helpful to provide the mass spectra figure of a representative sample.
Line 178-is the spiked solution from the standard chemicals or the SRM (line 166-SRM particles)?
QA/QC-are there any blank filters from the field sampling?
Without a direct measurement of gaseous organics, the whole discussion and interpretation on the gas-particle partitioning in this paper is very weak and inconclusive. There are also many other gas-particle partitioning models, of which there are very rough estimated numbers for some key parameter. The authors may still keep a small part of discussion on the partitioning and its impacts on the PMF results, however, it is not suggested to highlight this in the title and a long paragraph in the results/discussion part. Those only increased the length of the paper but not the depth and significance of the study, and to some extent have a negative impact of the manuscript organization.
The limitations in those apportionment methods including ratios as well as PMF have been widely recognized, however, these are still widely used nowadays. The limitations are briefly mentioned in some parts (lines 278-280). It is necessary and strongly suggested to have a separate section discussing the limitation of the study including sampling periods and methods used in source apportionment discussion.
Title- as mentioned “gas-particle partitioning” is not suggested to be highlighted here. Also “tracers for PM2.5 source apportionment” is a little confusing to me. The study did not investigate or evaluate the use of specific trace organics in PM2.5 source apportionment. What they did is the use of these tracers, together with ions, to run PMF and to identify potential sources of PM2.5.
Strongly suggest the authors to rethink the title for this manuscript.
Line 18-19, suggest to add the quantitative percentages, and the implication of different size distributions between PAHs and hopanes, - sources?
Lines 23-24, no new information added to the current knowledge as this trend has been widely recognized by the researches in this area. Also high uncertainties in these quantitative numbers as this is from a simple model estimation. Suggest to remove.
Line 109- “Han et al., 2018” is missing in the reference section
Lines 231-232, provide references
Line 236, is this a daily average or seasonal?
Line 237-238, the sentence “which was estimated…” may be moved to line 237 after the phase “organic matter (OM)”
Line 242, “daily average concentration’
Lines 243-244, what’re the quantitative percentages of these studies? It is interesting but also a little strange that the results were comparable in a fast-developed area (PRD), the marine aerosol (south China sea study), and the present city in inland. Please provide results and study periods in these literature and discuss if applicable.
Lines 243-251, when comparing to literature data, it is important and necessary to clarify the study period and year of those in literature. Some data in Table 3 are the annual average, while some are the monthly or maybe daily average. A simple comparison, to the wintertime study in this paper, and the high/low contamination conclusion here is not acceptable.
Figure 2- is the left circle PM2.5- inconsistent with the legend. Only 5 site results? The area of those might be adjusted to reflect the mass concentration. Also, please pay attention to the significance figures. Did the measurement technology provide an accuracy of 0.01 µg/m3?
Line 307- “emissions were similar”, or the alkanes are more likely homogeneously distributed across different sites?
Line 326, the peak in “9.9-18 µm” is very tiny
Figure 5- suggest to find another way to improve the presentation of these data. for example, maybe monitoring data from the present study can be in the same white or black sign as spatial distribution is not discussed here.