Impact of COVID-19 Mobility Changes on Air Quality in Warsaw

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We would like to thank you very much for your valuable comments. You can find our detailed responses in the attached file.

Yours faithfully,

Artur Badyda.

Author Response File: Author Response.docx

Reviewer 2 Report

This work evaluated the impact of Covid-19 on traffic volumes and NO2 and PM concentrations in Warsaw.  This is an interesting work.  Authors have benchmarked the results to the literature.  However, the novelty of this work should be highlighted and distinguished from the literature.  Some tables and figures are lack of interpretations.  Without interpretations, readers are not confident in the validity of the results, which may weaken the quality of the work.  Some tables and figures are lack of cross-references in the text.  Some citations are not consistent in the format.  Specific comments are as follow.

Line 55:  For citation “1”, please be consistent with the format for other citations in the manuscript.

Line 62:  Why is Poland practicing removing particulate filters from new diesel vehicles?  What is the purpose of this action?

Line 65:  For citation “2”, please be consistent with the format for other citations in the manuscript.

Lines 69-72:  “This is connected with … wide straight sections).”  How did the authors know this?  Need citation(s).

Line 94:  What is ITS?  Please define.

Line 117:  Why was there an increase in car use from 53% to 66% in Germany?  Because of the removal of lockdown restrictions?  Needs explanation.

Lines 152-154:  This is what the authors did, but most importantly, why did the authors do it in this way?  Why were the data acquired for 3 pandemic phases?  Why did the authors select Tuesday, Wednesday, and Thursday as representative working days?  Please provide the basis for these choices.  In addition, how did the authors quality assure the mobile phone operator data?

Line 157:  For citation “3”, please be consistent with the format for other citations in the manuscript.

Lines 165-174:  For the description of Table 1, authors just “read” the table to reviewer.  However, what are the interpretations of these trends?  For examples, why is the reduction in Phase 3 much smaller than that in Phase 1?  Why was there an increase in type of travel for some areas in Phase 2 and Phase 3?  Without interpretations, reviewer is lack of confidence in the validity of the results.

Lines 178-181:  Why did authors care about the morning peak?  Please provide the reason for making this analysis?  Why did authors not care about the afternoon peak?

Lines 186-189:  Why did the number of trips increase from Warsaw to the area around Warsaw for the three phases, while all other numbers decrease?  Does it make sense?  Need interpretations.

Line 194:  Where is the interpretation of Figure 1?  In addition, reviewer does not observe any cross-references in the text with respect to Figure 1.

Line 210:  The section number is wrong, should be 4.  Please also correct the following section numbers in the manuscript.

Line 225:  Reviewer does not observe any cross-references in the text with respect to Figure 2.  In addition, where is the air quality monitoring station in the picture?  Please clearly label the air quality monitoring station.

Lines 226-227:  Are NO2 concentrations really fairly constant in the past 15 years?  For Al. Niepodległości, NO2 concentrations in 2006 were about 40% higher than those in 2012.  Please rewrite this sentence for accuracy.

Line 227:  How did the authors know the values are “significantly” higher?  Did the authors do statistical analyses at a significance level?  Reviewer did not observe any error bars in Figure 3 to indicate confidence intervals at a statistical significance level.

Line 235:  Figure 3 – please provide axis titles in the figure and also add units for NO2 concentrations in the y-axis title.

Line 238:  How did the authors quality assure the readings from air quality monitoring stations?

Lines 250-252:  Does Figure 5 refer to NO2 concentrations based on peak traffic hours on Tuesdays, Wednesdays, and Thursdays?  If so, need to be clear in the caption of Figure 5.

Line 269:  How did the authors know NO2 concentrations in March-April are “significantly” lower than those in May-June?  Reviewer did not observe any error bars in Figure 3 to indicate confidence intervals at a statistical significance level.  Reviewer is not confident the difference between 34 ug/m3 and 43 ug/m3 is significant unless authors show results for statistical analyses.

Line 281:  Why did not the authors mention the afternoon peak earlier?  The manuscript needs to be reorganized to interpret results in a logical order.

Lines 287-295:  Reviewer does not observe any cross-references in the text with respect to Table 3, Figure 6, and Figure 7.  Please add cross-references for these tables and figures in the manuscript.  Without cross-references, reviewer does not know what these tables and figures are used for.

Lines 296-301:  The interpretation here is weak.  Isn’t the traffic volume also lowest during night hours and then begins to rise during morning peak hours?  If so, why is the correlation weak between NO2 concentrations and traffic volume during the morning peak hours?  Reviewer suggests authors make correlation analyses to quantify the correlation between NO2 concentrations and traffic volume for morning peak versus afternoon peak, respectively.

Line 309:  For citation “4”, please be consistent with the format for other citations in the manuscript.

Line 319:  For citation “5”, please be consistent with the format for other citations in the manuscript.

Line 323:  For citation “6”, please be consistent with the format for other citations in the manuscript.

Lines 306-331:  Although the information regarding emission sources for various pollutants in Poland is good, reviewer is confusing why such information is needed in this work.  This information seems out of the scope of this work.  Did the authors make any analyses to evaluate the impact of Covid-19 mobility changes on air quality for pollutants such as ammonia, SOx, Hg, NMVOC, PAH, CO?  If not, why are these needed?  Reviewer suggests taking out unnecessary information.

Line 344:  Please quantify how much higher (e.g., XX% to YY% higher).

Lines 351-353:  Figure 9 – please provide axis titles in the figure and also add units for PM concentrations in each y-axis title.

Lines 354-357:  Needs interpretation.  Why did PM reduce as the volume of traffic generated increased?  Don't vehicles in the fleet generate PM emissions?  Did the authors assume the increase in PM emissions due to increased traffic volume is less than the decrease in PM emissions due to decreased burning of solid fuels in households?  If so, why?

Lines 403-408:  It is good to benchmark the authors’ work to the literature.  However, if the results in the authors’ work are all consistent with the literature, then what is the novelty of the authors’ work?  What new things can readers obtain from the authors’ work rather than from the literature?  What knowledge gaps did the authors address in this work but did not exist in the literature?  Authors need to highlight the novelty of the work.

Author Response

Dear Reviewer,

We would like to thank you very much for your valuable comments. You can find our detailed responses in the attached file.

Yours faithfully,

Artur Badyda.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thanks for revising the manuscript. Yet most comments have been addressed, I suggest that the introduction section needs to more clearly mention the aims of this research.

Author Response

Dear Reviewer,

Thank you for the acceptance of the modifications of our manuscript and for your recent suggestion. We added a new paragraph at the end of the Introduction section in which we mentioned the aim of the research described in the paper.

Yours faithfully,

Artur Badyda.