Visibility Driven Perception and Regulation of Air Pollution in Hong Kong, 1968–2020

Round 1

Reviewer 1 Report

I had studied the manuscript entitled "Air pollution, visibility and health in Hong Kong, 1968-2020", this study uses air pollutants monitoring data with visibility, health risks and number of Google search times to analyze long term correlation on air quality in Hong Kong, this is an interesting idea to realize the issue on air quality, but the manuscript looks like kind of report but not scientific research paper. From scientific viewpoint, it is unclear to see the correlation between the four factors from the manuscript. Moreover, air pollution has to consider the emission, meteorology(climatology), as well as the topography, for example, Hong Kong is located below Guangdong, China, and is easily affected by the upstream transportation of pollutants. But in this manuscript, only using a case of the countryside and the city, it is impossible to understand or have new finding on air quality issues.  Title of this manuscript is also not suitable, no main issue on it. I strongly suggest author could think about the basic theories on air quality more seriously and modify the study with more scientific description.  The following is my specific comments:

1. Title should be changed

2. What is the reference of the equation in L206? And how to calculate the coefficient of the equation? 

3. Section 3.1 (In L186-L225), author did not explain the correlation between PM2.5 and visibility, is there any evidence to prove the results in atmospheric sciences? There are the same situation in Section 3.2 (L238), the correlation between pollutant PM2.5 and AQHI, and Section 3.3 (L308-L342), "visibility is related to PM2.5 and AQHI". Statistics results can not present the "real" in sciences.
4. In L147 to L157: Please explain the reason of visibility comparison between airport and HKO? Are they have significant characteristics on air quality? I can not see the correlation between various pollutants and visibility  in Figure 2(c)-(f), please explain it.
5. The previous narratives all describe the period from 1998 to 2020, but and in figure 5 the range of data description is 2000 to 2020, any error on it or there is some reason? Please add the note on manuscript.
6. In L355, it shows that NOx and particulate matter are reduced, but ozone is increased. We all know the precursors of ozone are mostly from VOCs and NOx, It is recommended that this study incorporate VOCs observational data for joint evaluation, or author need to prove Hong Kong is NOx dominated area on ozone issue.
7. L374-L387, the conclusion, it learned from the discussion that the number of media discussions, visibility and air pollution are not strongly correlated, I can not see any new finding on scientific results briefly. Author need to highlight the innovation in this manuscript.

Author Response

I had studied the manuscript entitled "Air pollution, visibility and health in Hong Kong, 1968-2020", this study uses air pollutants monitoring data with visibility, health risks and number of Google search times to analyze long term correlation on air quality in Hong Kong, this is an interesting idea to realize the issue on air quality, but the manuscript looks like kind of report but not scientific research paper. From scientific viewpoint, it is unclear to see the correlation between the four factors from the manuscript. Moreover, air pollution has to consider the emission, meteorology(climatology), as well as the topography, for example, Hong Kong is located below Guangdong, China, and is easily affected by the upstream transportation of pollutants. But in this manuscript, only using a case of the countryside and the city, it is impossible to understand or have new finding on air quality issues.  Title of this manuscript is also not suitable, no main issue on it. I strongly suggest author could think about the basic theories on air quality more seriously and modify the study with more scientific description. 

THE MS IS NOT TRYING TO ARGUE THAT VISIBILITY IS RELATED TO AIR POLLUTION AS THAT HAS LONG BEEN EXPLORED THE KEY NOTION IS THAT AS NOTED IN THE Ms; "Visibility is a perceptible indicator of air pollution, so it is hardly surprising that it has been used to promote the regulation of air pollutants. " THIS IS STRESSED MORE IN THE REVISIONS, BUT THIS IS WHY QUESTIONS OF EMISSION METEOROLOGY TOPOGRAPHY ARE NEGLECTED. IN REALITY IT IS MORE ABOUT THE EFFECT OF VISIBILITY OF AIR POLLUTION, NOT THE OTHER WAY ROUND  THIS IS STRESSED IN THE INTRODUCTION "This paper looks at the relationship between visibility and air pollution, but is mostly concerned with the effects these have on health, public perception and policy. It will not treat the relationship between the aerosol composition and visible range, but consider a loose relationship between air pollution and perceptions of visibility. "

The following is my specific comments:

Title should be changed
UNDERSTAND THIS, AS I HAVE STRUGGLED A LONG TIME WITH THE TITLE. IT IS NOW CHANGED TO "Visibility driven perception and regulation of air pollution in Hong Kong, 1968-2020 "

What is the reference of the equation in L206? And how to calculate the coefficient of the equation? 
THE EQUATION IS A MULTILINEAR REGRESSION SOLVED AS DESCRIBED IN THE METHODS. EXPANDED THE TEXT ON THIS 

Section 3.1 (In L186-L225), author did not explain the correlation between PM2.5 and visibility, is there any evidence to prove the results in atmospheric sciences? There are the same situation in Section 3.2 (L238), the correlation between pollutant PM2.5 and AQHI, and Section 3.3 (L308-L342), "visibility is related to PM2.5 and AQHI". Statistics results can not present the "real" in sciences.

IT IS TRUE, BUT THIS IS TAKE AS THE RESULT OF PREVIOUS WORK (NOTABLY THAT OF WANG, SEQUERIA ETC) SO WAS NOT EXPLORED HERE, BUT WAS PART OF THE INTRODUCTION- AND ALSO INTRODUCED IN THE OPENNING PARAGRAPH TO REMIND THE READER OF THE KEY HONG KONG REPORT "Study of Visibility Reduction and its Causes in Hong Kong ". TEXT CHANGED TO ITALICS SO TO EMPHASISE THIS REPOR. THE RELATIONSHOIP BETWEEN AQHI AND PM2.5 IS FROM (WONG REFERENCE 38) SO IT HAS BEEN ADDED TO THE TEXT AT THIS POINT. 

AGREE, BUT THERE IS NO CAUSALITY IMPLIED BY THE STATISTICS. THE ORIGINAL WORDING WAS "Although not perfect the relationship supports the view that pollution and visibility are related, a link, likely indirect, that aligns with public expectation"  THIS HAS BEEN EXPANDED "Pollutant gases are hardly a driver of visbility, but the relationship supports the view that pollution as measured by the HKEPD network and visibility are related, a link, likely in-direct, that aligns with public expectation "  

In L147 to L157: Please explain the reason of visibility comparison between airport and HKO? Are they have significant characteristics on air quality? I can not see the correlation between various pollutants and visibility  in Figure 2(c)-(f), please explain it.
GOOD POINT THIS IS NOW EXPANDED IN GREATER DETAIL TO READ "The visibility at the airport is shown in Fig. 2b, and although it initially has more hours of low visibility it improves rapidly and continuously from peaks early in the 21st century, showing a rather similar change over time to that at the HKO, suggesting that these changes are widely experienced across the territory."

GOOD POINT FIG 2C-F ARE MERELY THERE TO SHOW CHANGES IN POLLUTION OVER TIME THAT ARE EXPLORED LATER, ALTHOUGH IT IS WORTH NOTING THE TRENDS OCCUR MAY RELATE TO VISBILITY.   ADDED THE WORDS "However, from about 2005 the number of hours of low visibility gradually decreases and loosely aligns with improvements in PM, NO2, SO2, though not O3 (Figs 2c-f). "

The previous narratives all describe the period from 1998 to 2020, but and in figure 5 the range of data description is 2000 to 2020, any error on it or there is some reason? Please add the note on manuscript.
GOOD POINT ADDED AS" Hong Kong’s English language newspaper the South China Morning Post published 70 articles on air pollution from December 2018 – December 2020, to hint at current perceptions. "

In L355, it shows that NOx and particulate matter are reduced, but ozone is increased. We all know the precursors of ozone are mostly from VOCs and NOx, It is recommended that this study incorporate VOCs observational data for joint evaluation, or author need to prove Hong Kong is NOx dominated area on ozone issue.
I HAVE MADE THE POINT, BUT AS MENTIONED IT IS WELL KNOWN. THE INTENT HERE WAS NOT TO ESTABLISH THE DRIVER OF HOMG KONMG'S OZONE INCREASE, BUT I ADD A REFERENCE (Xue, L., Wang, T., Louie, P. K., Luk, C. W., Blake, D. R., & Xu, Z. (2014). Increasing external effects negate local efforts to control ozone air pollution: a case study of Hong Kong and implications for other Chinese cities. Environmental science & technology, 48(18), 10769-10775.) TO THAT TO AVOID A LENGTHY DEBATE ON THE MECHANISM. 

L374-L387, the conclusion, it learned from the discussion that the number of media discussions, visibility and air pollution are not strongly correlated, I can not see any new finding on scientific results briefly. Author need to highlight the innovation in this manuscript.

AGREE, BUT SCIENTIFIC DISCOVERY WAS NOT THE INTENT OF THIS PAPER IT IS MUCH MORE ABOUT THE INFLUENCES ON POLICY AND PERCEPTION THE REASON THE PAPER WAS SENT TO "MDPI ENVIRONMENTS" AS ITS AIMS SAY IT IS INCLUDES DISCUSSIONS OF "risk, policy, governance, monitoring and modelling of environmental systems, stakeholder engagement and decision support. ". THE NOVELTY IN THIS HAS NOW BEEN STRESSED IN THE CONCLUSION SHOWING THAT THE PAPER ADDRESSES THE AIMS OF THE PAPER AND CONCERN: "with the effects these have on health, public perception and policy."

Reviewer 2 Report

Dear Author,

The paper is well written, and in concrete way. I have only few suggestion listed below:

Line 35-36 – Author wrote about some problems in UK, Italy and Greece in the past, but nowadays the air pollution is also a problem in African countries, where the industry is a pollutes of air, water, land e.g Guinea Conakry (Environmental pollution as a threats to the ecology and development in Guinea Conakry). Maybe it would be good to write that problem is not only from the past. And currently is very important in developing African countries. The smell of “heavy air”, destroyed water, beach and influence on health is easy visible in Guinea.

Line 228 – Author wrote, that air pollutants and health risk changed over time. It would be valuable to explain who are the “poisoners” and which activities produce NOx, Sox, CO2. Who is responsible for pollutions?

After supplementing with the mentioned issues, the article can be published

Author Response

The paper is well written, and in concrete way. I have only few suggestion listed below:

Line 35-36 – Author wrote about some problems in UK, Italy and Greece in the past, but nowadays the air pollution is also a problem in African countries, where the industry is a pollutes of air, water, land e.g Guinea Conakry (Environmental pollution as a threats to the ecology and development in Guinea Conakry). Maybe it would be good to write that problem is not only from the past. And currently is very important in developing African countries. The smell of “heavy air”, destroyed water, beach and influence on health is easy visible in Guinea.

GOOD POINT AND THIS IS ADDED AS ", and continue to offer the potential to extend records in countries where monitoring data covers a relatively short period. "

Line 228 – Author wrote, that air pollutants and health risk changed over time. It would be valuable to explain who are the “poisoners” and which activities produce NOx, Sox, CO2. Who is responsible for pollutions? 

THIS IS ADDED AS  " In Hong Kong power stations have long been an important source of air pollutants, but they have improved, such that shipping has become a more dominant source, especially for SO2. Road transport is relevant to NO2, and the volatile organic emissions and carbon monoxide contribute as precursors in the production of O3."

After supplementing with the mentioned issues, the article can be published

Reviewer 3 Report

“Air pollution, visibility and health in Hong Kong, 1968-2020” is easy to read. Although it lacks of originality and new outcomes. My suggestion is that the authors revise their objectives, and write the conclusions according to those objectives. The objectives refer “…but is mostly concerned with the effects these have on health…” and the conclusions related with this point are scarce.

Some specific comments/suggestions are presented below:

Lines 162 to 184 – The contents of these lines are not results. Section 3 has also some discussion.

Line 213 - is it 85% or 95%?

Section 3.2 – should be clearer how equation in line 244 was obtained. In my opinion, since this is not a result of the present work, this should be in section 2 (Materials and Methods). Only Figure 3 and its explanation are a result of the present work.

Line 255-  r2~0.88 is a result obtained with the data used in the present work? Please explain better.

Table 1 – As it is not a result of this work, reference should be included in the table and, in my opinion, it should be moved to section 2. How was Table 1 used in this work?

Author Response

“Air pollution, visibility and health in Hong Kong, 1968-2020” is easy to read. Although it lacks of originality and new outcomes. My suggestion is that the authors revise their objectives, and write the conclusions according to those objectives. The objectives refer “…but is mostly concerned with the effects these have on health…” and the conclusions related with this point are scarce.

THIS IS TRUE, BUT TO BE FAIR THE FULL SENTENCE READS "This paper looks at the relationship between visibility and air pollution, but is mostly concerned with the effects these have on health, public perception and policy. "  I HAVE CHANGED THE CONCLUSIONS TO MAKE SURE THESE ARE EACH ADDRESSed

Some specific comments/suggestions are presented below:

Lines 162 to 184 – The contents of these lines are not results. Section 3 has also some discussion.  THIS IS A GOOD POINT. THE RESULTS AND DISCUSSION WERE ONTERLEAVED, SO THE SECTION NAME HAS BEEN CHANGED TO RESULTS AND DISCUSION 

Line 213 - is it 85% or 95%? THANKS, THAT HAS BEEN CORRECTED

Section 3.2 – should be clearer how equation in line 244 was obtained. In my opinion, since this is not a result of the present work, this should be in section 2 (Materials and Methods). Only Figure 3 and its explanation are a result of the present work.  AGREE THIS HAS BEEN MOVED TO METHOD SECTION

Line 255-  r2~0.88 is a result obtained with the data used in the present work? Please explain better.  WORK DONE HERE SO NOTED

Table 1 – As it is not a result of this work, reference should be included in the table and, in my opinion, it should be moved to section 2. How was Table 1 used in this work? GOOD POINT IT WAS NOT USED IN THE FINAL MS SO HAS BEEN DELETED

Round 2

Reviewer 2 Report

Dear Author,

Thank you for your response. I noticed that you added one very "soft", general sentence about other countries, but air pollution in African cities is such a big problem that apart from Italy and Greece, it's worth mentioning Africa by name. The author wrote the example of European countries, but for reasons of pollution due to economic problems, Africa also deserves to be cited. You can use the article on environmental pollution in Guinea Conakry

Reviewer 3 Report

The author attended most of the suggestions.