Quantifying the Influences of PM2.5 and Relative Humidity on Change of Atmospheric Visibility over Recent Winters in an Urban Area of East China
Round 1
Reviewer 1 Report
In the paper “Quantifying anthropogenic and natural influences on change of atmospheric visibility over recent winters in an urban area of East China” considered here for the publication on the journal “Atmosphere” (manuscript number atmosphere-778989) the authors analyze the relationship between visibility and atmospheric parameters, both natural and anthropogenic such as relative humidity and PM2.5 respectively.
It is a very interesting topic with many kinds of implications; conclusions exposed are supported by a good data elaboration.
Paper is well written; theoretical and technological aspects are clearly exposed.
Also references are sufficient to support the work.
In my opinion this work should be published after a minor revision.
Specific comments:
- Please reduce the number of significant digits (2-3 are sufficient) used at line 168. Please check for this detail throughout the entire manuscript.
- About the references, the ratio between old (later than 5 years) and new (within 5 years) references should be balanced.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please read my report.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Quantifying anthropogenic and natural influences on change of atmospheric visibility over recent winters in an urban area of East China.
By Sun et al.
This article studies the influences of fine particles (PM2.5) and relative humidity (RH) on atmospheric visibility during the wintertime in Nanjing, an urban area of eastern China, from 2013 to 2019. In order to quantify the relative contribution of anthropogenic (PM2.5) and natural (RH) factors to the variations of atmospheric visibility, the authors use daily means of visibility, RH and PM2.5 concentrations, computed from hourly observational data. They show a significant negative correlation between visibility vs PM2.5 and RH. They also show that visibility presents a power-law relationship with the PM2.5 and RH. Based on the obtained results, they conclude that, compared with the anthropogenic PM2.5 factor, the natural RH factor has a more important impact on the atmospheric visibility in the region of Nanjing.
General Comments
It is well known that both PM2.5 concentrations and meteorological parameters, mainly RH, have an impact on the variations in visibility. However, in some cases, these variations are mainly determined by PM2.5 concentrations, and so visibility can very well represent the level of air quality. In contrast, in the cases where RH dominates the variations in visibility, the visibility may not be a good proxy of air quality. Besides, it is not clear if there are threshold values for concentrations of PM2.5 and HR that define the conditions under which visibility could be used to assess air quality. In this context, this paper presents some insights.
Although the analysis is quite straightforward and the effort of this work seems substantial, the application of these results will improve the representativeness and reliability of the use of visibility in the field of air pollution attribution and the determination of its climatic effects. This would warrant publication. However, there are several specific comments on the manuscript (listed below) and one major concern that the authors should address before recommending publication.
1) My main concern is the methodology used in the data analysis. This study should take into account some considerations, such as those listed below, that could have an impact on the results:
- Regarding visibility, it can be assumed that automatic weather stations collected hourly visibility data. In this case, the effects due to the limited range of the instruments should be avoided. Thus, data beyond the maximum observed visibility should be excluded
- Atmospheric horizontal visibility can be affected by some weather phenomena such as, fog, precipitation, and long-range transport of air pollutants, which causes haze occurrences. Thus, certain criteria must be applied in order to remove these influences (e.g. Wang et al., 2019).
- Uncertainty of the relationships between RH and visibility. The standard deviation of visibility within specific ranges of PM2.5 concentrations and RH can be used to express the uncertainty of these relationships (e.g. Wang et al., 2019).
Wang, X., Zhang, R., & Yu, W. (2019). The effects of PM2.5 concentrations and relative humidity on atmospheric visibility in Beijing. Journal of Geophysical Research: Atmospheres, 124, 2235–2259. https://doi.org/10.1029/2018JD029269
2) In order to highlight any significant findings of this study, comparisons with other studies may be beneficial to the paper.
Specific Comments
Some of the sentences are long and hard to follow. I would encourage the authors to break down long sentences so that they would be easier to follow. Please use grammar checker to improve the clarity of the content.
Page 1, line 16: Change “ambient atmosphere” to “the ambient atmosphere”
Page 1, lines 20-28: The sentence is long and not clear. Please re-word, preferably split into short sentences. Use a grammar checker.
Page 1, line 39; Replace “leaded” with “led”
Page 2, line 52: Change “aerodynamically” to “aerodynamic”
Page 2, lines 54-55: Please revise the wording “Deterioration in visibility is mainly driven to a large extent by enhancing concentrations of secondary aerosols PM2.5”
Page 3, line 101: What was the criterion used in the definition of interval limits to define, good, weak, and poor visibility?
Page 4, line 132. Figure 2: It would be helpful to add monthly variations of PM2.5 and RH. That would help to better interpret the winter relationships between visibility, PM2.5, and RH in Nanjing.
Page 4, line 137-10. The decreasing trend in visibility between 2013 and 2019 could also be explained by the slight increase in humidity during these winter periods, which could intensify the hygroscopic growth of aerosol particles, thus increasing light extinctions and reducing visibility.
Page 5, line 152-158. Please check the wording. The applications of the criteria for filtering data, mentioned in the general comments section, could have an impact on the correlation between visibility and HR and PM2.5 and thus affecting conclusions.
Page 5, line 161. Change “frequencies of good …” to “daily occurrence frequency of good …”
Page 8. Line 237. Section 3. 3. What would be the contribution of long-range transport of PM2.5, compared to local PM2.5, in the variation of visibility?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Dear authors, I appreciate the corrections made to the manuscript. I also agree with the justifications made to my main concerns. Mainly to the issue related to the impact of long-range transport of air pollutants on visibility impairment. I strongly encourage the authors to analyze this issue in more detail, in the near future, by means of a more comprehensive numerical model of air quality and meteorology.
Therefore, I recommend the revised manuscript for publication.
