From the journal Environmental Science: Atmospheres Peer review history

05-Aug-2023

Dear Dr BAHINO:

Manuscript ID: EA-ART-07-2023-000108
TITLE: Spatio-temporal variability of PM2.5 in two West African cities, Abidjan (Cote d’Ivoire) and Accra (Ghana)

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

After careful evaluation of the manuscript and reviewers’ comments, I regret to inform you that I do not find your manuscript suitable for publication and therefore it has been rejected in its current form.

Both reviewers were supportive of more observations and analyses of PM in Africa, and I strongly agreed with this view. However, both reviewers pointed out the lack of novelty in the data reported in this study, the overstatement of novelty and implications, and the lack of context with respect to the other published studies for this region. Both reviewers recommended a more thorough review of the literature, proper identification of the knowledge gap with regard to the source of PM in this region, and the drawing of data-supported conclusions from your measurements.

However, if you are able to fully address the concerns raised by the reviewers in the reports below, I will consider a substantially rewritten manuscript which takes into account all of the reviewers’ comments. If you choose to resubmit your manuscript, please include a point by point response to the reviewers’ comments and highlight the changes you have made.

Your manuscript will receive a new manuscript ID and submission date and further peer review will be necessary. Please note that re-submitting your manuscript does not guarantee its acceptance in Environmental Science: Atmospheres.

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I look forward to receiving your re-submission.

Yours sincerely,
Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

************

Reviewer 1

The authors deployed field-calibrated low-cost sensors in West Africa, for over a year with PM2.5 concentrations. Though researches on the atmospheric issues in West Africa are very necessary, this study on the spatial-temporal variability of PM2.5 is unbacked with lots of guesswork and extrapolation. I feel the data quality of the current manuscript is not strong enough to be published in Environment Science: Atmospheres. Here are some specific comments which I hope the authors would find helpful during the revision.
1. The introduction about Abidjan and Accra seems tedious. I suggest the authors shorten the current Section 2.1 and remove the detailed information to the supplementary information.
2. The data bias detected by the RAMP shows some kind of correlation with the RH (Figure 3). Why does this kind of bias arise? Is it related to the design of the instrument? More discussion should be added.
3. For Section 3.1, I don’t feel the novelty of the PM2.5 data alone is strong enough to support the whole section. Factors like boundary layer height, emission types, etc. have been mentioned without in-depth analysis.
4. In Section 3.4, the HYSPLIT back-trajectories model deployed here is a good demonstrator to prove the air mass source. However, the presentation of the results is confusing. It seems dizzy to present so many subfigures with limited information. I suggest the author reorganize Figure 10, 11, & 12, with subfigures such as “before, during, and after the event”.

Reviewer 2

Summary and major comments

Air pollution monitoring in SSA is of vital importance as cities in this region have some of the fewest institutionalized long-term air quality monitoring schemes, but some of the highest recorded concentrations. This paper summarises the diurnal and seasonal variations of PM2.5 air pollution concentrations measured at 4 sites in Accra and 5 sites in Abidjan and compared levels to WHO guidelines. The methods are largely sound, and the results will be of interest to air pollution researchers, practitioners, and environmental policy makers in these cities. However, as a reviewer, I am also aware that there is already a fairly substantial body of research that has been conducted in Accra, on air pollution monitoring and modelling, which includes PM10, PM2.5, BC, and NO2. These long-term monitoring studies have, since 2010, and as recent as 2023, looked at diurnal variations, seasonal variations, spatial patterns, modelled and predictions concentrations in high resolution, and looked at local and regional sources and source apportionment. This paper would benefit from a more thoughtful review of the breadth of work that has already been conducted in these cities and how their own paper’s contributions are situated within it. Otherwise, it feels like the authors are being disingenuous about existing studies. With that said, this paper needs to clearly indicate their contribution to the exiting literature in the region or the study cities. Possibly, one of their main messages is that LCS underestimate in high pollution harmattan periods in West Africa?

In a similar way, the authors need to discuss their results (compare and contrast) in the context of existing research since previous papers have already found and discussed many of the key findings that this paper presents (in Accra for example).

For instance, here are some links to papers for your reference

Accra (Ghana)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf
https://pubs.acs.org/doi/10.1021/es903276s
https://www.sciencedirect.com/science/article/pii/S0048969712009102?via%3Dihub
https://www.sciencedirect.com/science/article/pii/S0048969723011981
https://www.sciencedirect.com/science/article/abs/pii/S0048969708004683
https://iopscience.iop.org/article/10.1088/1748-9326/8/4/044025
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GH000247 (e-waste sites)
Accra (Ghana) and cities in The Gambia
https://pubmed.ncbi.nlm.nih.gov/24351083/

Specific comments

[1] The authors state several times throughout the paper, including in the abstract, that this is the first study to look at diurnal patterns of PM2.5 in places like West Africa. This, however, is not the case. These statements throughout the paper should be updated to more accurately reflect the work that has already been done in this area. This will allow the authors to more clearly indicate their contribution to the emerging evidence on PM2.5 in the region.

For example, Alli et al 2021 looked at and reported on diurnal and seasonal patterns of PM2.5 in Accra using data from 10 representative sites throughout the city (monitored for 1 year) and 136 representative sites in the city (monitored for weeklong periods) (e.g., see section 5.3 and Fig 5 in Alli et al 2021). Alli’s paper used filter-corrected minute-by-minute data.

Furthermore, back in 2010 Dionisio et al also looked at diurnal and seasonal patterns of PM monitored over a long period of time across 11 different neighbourhoods in Accra (e.g., see fig 3 in Dionisio et al).

Lastly Kwarteng et al 2020 looked at hourly average concentrations near e-waste sites in Accra.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf
https://pubs.acs.org/doi/10.1021/es903276s
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GH000247

[2] The paper’s title (‘Spatio-temporal…’) as well as statements throughout the paper (such as in the Abstract: ‘This study aims to provide high quality spatiotemporal data on PM2.5…’) make claims about the data providing high spatial resolution information, however, I am not sure how the authors can justify how 4 monitoring locations in Accra and 5 in Abidjan can provide high spatial resolution data? Cities like Accra for example, can have PM2.5 levels which vary significantly over small spatial scales, as was shown previously by Rooney et al in 2012, Dionisio et al 2010, and Alli et al 2021.

The collection of data between cities (Accra vs Abidjan) is indeed interesting, though I would not consider 4 and 5 measurement sites in each city as providing high-resolution spatial data and would recommend that the authors revise statements in their paper to more accurately reflect that, and perhaps focus on the comparative aspects between the cities.

https://www.sciencedirect.com/science/article/pii/S0048969712009102?via%3Dihub
https://ehp.niehs.nih.gov/doi/10.1289/ehp.0901365
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf

[3] Can the authors describe how they sampled and chose the sites where they monitored at? Was it random sampling, purposeful sampling, convenience sampling? How might this sampling strategy impact the results they found?

[4] I feel that section 3.5 and Fig 13 are better suited for the Discussion section as they are not a result of this study.

[5] As Fig 13 does not include references to the publications it pulls results from, the figure legend should at least direct readers to Table SI 6 where this information can be found. Furthermore, I would also suggest adding results from studies such as Rooney et al 2021 to Fig 13 and in Table SI 6.

https://www.sciencedirect.com/science/article/pii/S0048969712009102?via%3Dihub

[6] PM2.5 annual average concentrations are changing over time in many SSA cities. Therefore, it may be useful to add years in which measurements were conducted to Fig 13 as its possible that differences observed between places are actually influenced by the years in which measurements were conducted.

[7] Many of the descriptive statistics given for the 4 sites in Accra (diurnal patterns, day of the week, seasonal, and comparison to WHO guidelines) are the same types of descriptive summaries that were reported for 146 sites in Accra in the study by Alli et al 2021. I think it would be useful to compare the results between these two studies and comment on any similarities or differences, and if differences are found, why might that be (in the Discussion section)?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf

[8] In the Introduction (First paragraph, page 2), the authors make several statements about studies evaluating respiratory and cardiovascular health effects, as well as statements about the methods for data collection used in those studies, however many of these statements are incorrect and/or the references attached to them are incorrect. I would encourage the authors to take a closer look at all of the references used throughout their paper and ensure statements are cited properly.

Some examples:

The authors state that ‘…..The respiratory health effects of exposure to PM2.5 have also been evaluated in Abidjan and Cotonou 8,12, Accra 13–16; Lomé 17 and Bamako 11……’. However, respiratory health effects were not evaluated in references 14 (Malley et al), 15 (Arku et al) or 16 (Delapena et al) (unsure of the other references, but these should be checked also).

The following statement is also incorrect as the study by Alli et al 2021 (ref 22) did in fact look at diurnal patterns with time-resolved filter corrected data ‘…..As well, A study providing weekly averaged data over a period of nearly a year was conducted in Accra at fixed and mobile sites using filters and low-cost devices 22 . These low temporal resolution studies do not allow analysis of diurnal, daily variations of PM2.5 concentrations, nor can these results be compared to annual WHO guidelines when conducted over period of less than one year……’

[9] Section 2.2, Measurements were collected between February 2020, and Nov 2021. Can the authors comment on what the impacts of the COVID pandemic and city-wide lockdowns might have been in terms of an interruption of measurements, but also changes in pollution levels?

[10] On Page 19, the Authors state that they hypothesize that this region could have received dust from the Saharan desert. Though this has already been hypothesized and established in previous studies. Furthermore, this question has already recently been explored in the paper by Wang et al 2022 for Accra using the HYSPLIT model. I would recommend that the authors refer to that paper as well and incorporate a summary on how their results/findings compare.

https://www.sciencedirect.com/science/article/pii/S0048969721050063?casa_token=OGHg5mfca8gAAAAA:ACO40bHjZrLHtO0ASH8fmKMrSfPFRIW7mU5Hjl1qm72EQvx1UYKLlmRWEKCJDSEaum1VQFTxH4Q

Minor comments
• The paper could benefit from some text editing throughout and could be more concise when describing results.
• Double check the area (km2) size of the GAMA that is reported here as other sources/papers report a different size.
• Typo in Table 1 should read as ‘Residential and traffic’.

12-Feb-2024

Dear Dr Bahino:

Manuscript ID: EA-ART-01-2024-000012
TITLE: Spatio-temporal variability of PM2.5 in two West African cities, Abidjan (Cote d’Ivoire) and Accra (Ghana)

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

After careful evaluation of your manuscript and the reviewers’ reports, I will be pleased to accept your manuscript for publication after revisions.

Please revise your manuscript to fully address the reviewers’ comments. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

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Prof. Nønne Prisle
Associate Editor, Environmental Sciences: Atmospheres

************

Reviewer 1

I thank the authors for addressing all my points.

Reviewer 2

I thank the authors for addressing some of my comments and for their thoughtful responses, however, I still feel as if further revisions needed to recommend publication.

Since much larger studies have already been conducted in Accra in recent years (which also address spatial, diurnal, and seasonal variations, as well as the impact of Harmattan), the novelty of this study is the work in Abidjan as well as the potential for comparison between these two cities. I thank the authors for revising the manuscript so that the novelty in Abidjan is brought out more, however, I would suggest that the authors in the discussion make a more thorough comparison between these two cities, as that is one of their main stated areas of novelty in the introduction/aims. For example, what are the similarities/differences between these cities and what can this tell us about developing air quality monitoring systems in west Africa and policies to mitigate air pollution?

I previously made the comment that the wording of the title and aims need to be revised so that they do not overstate that this paper provides information on the ‘spatio-temporal variability of’ PM2.5, however the authors do not seem to have made this revision. I reiterate this point as the contribution of this data more appropriately should be the ‘temporal variability of…’ PM2.5 in these two cities. Having 4 sites in Accra and 5 in Abidjan, and often not all of the results across the 9 sites are presented, cannot justifiably give you information on spatial variability. By using that type of phrasing, it is misrepresenting the information that this data can provide.

Other comments

-Paper could benefit from grammatical editing and refinement

-There is a lot of text in the Results section that could benefit from condensing for brevity. Alternately, authors can also move some of this text over to the supplemental materials.

-Fig 5 - Interesting that the peaks between 5am – 8am at Atomic Interchange which is a traffic influenced site has the same PM2.5 levels as the site at the University of Ghana, which should reflect low background levels. Why do you think that is the case and can you provide comment in the discussion section?

- In the introduction you make the claim that there has been a lot of personal exposure studies in Accra, but limited field measurements because there is limited availability of equipment and its expensive. Though how would this argument also not apply to personal exposure data collection, which others argue is even more expensive, time-consuming and difficult to do?

-I don’t think you need to provide the formula for the IQR in the results which is a fairly well-known statistical summary measure. If you want to keep it, I suggest moving to the supplementary materials.

-Authors say they collected measurements at 9 sites (4 in Accra, and 5 in Abidjan) but often results from only 6 sites are presented (in text, figures (Fig 6, Fig 7a, Fig 7b, Fig 8, Fig 9, and tables (Table 2)). Can authors clarify and make clear in the paper that the majority of data presented in many cases is actually only from 6 sites (not 9) (and in the abstract if applicable)?

-Page 11 in the result (as well as in the discussion), the authors make comparisons between each day of measurements (i.e., % of days above guideline) with the WHO guideline, however, the guideline is meant to be an annual average, so it would be more appropriate to take the average or median at each site and compare that with the guideline.

-Fig 13 is blurry, can the resolution be improved?

-I previously made the comment to compare this paper's results in Accra to previous work done by Alli et al (2021) as many of the descriptive analyses are the exact same (albeit data collected in slightly different time periods and number of sites), however the authors did not address my comment with a response or by editing the manuscript.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf

- This sentence in the Discussion (Page 21) does not mean much without context on how large/extensive these 7 studies are, and I would argue that Accra already has some of the more thorough and largest studies characterising air quality in SSA. ‘....The small number of studies (only 7 publications) and these large values clearly warrants for further long-term measurements.’

-My previous comment about the potential impact of the COVID pandemic was not related to carrying out maintenance on the equipment but how changes in urban activities and transport during this time (i.e., less people leaving their homes) may have impacted the air pollution results of this paper. I would suggest adding this into your discussion section.

-In the abstract you don’t need to say how the study was funded. I would suggest removing the phrase ‘…funded by the Make Our Planet Great Again (MOPGA) program’.

Answers to Editor and reviewers Manuscript N° EA-ART-01-2024-000012

The authors would like to thank the editor and reviewers for their valuable feedback, which has significantly contributed to enhancing the quality of this manuscript submitted for publication in Environmental Sciences Atmosphere.
Referee 1 expressed satisfaction with the provided responses, while referee 2 offered additional comments for consideration. Below, we present our responses and the modifications implemented in accordance with their recommendations.
All changes and additions are highlighted in yellow in the final version of the manuscript.

Referee 2:
Comments to the Author
General comments
A) I thank the authors for addressing some of my comments and for their thoughtful responses, however, I still feel as if further revisions needed to recommend publication. Since much larger studies have already been conducted in Accra in recent years (which also address spatial, diurnal, and seasonal variations, as well as the impact of Harmattan), the novelty of this study is the work in Abidjan as well as the potential for comparison between these two cities. I thank the authors for revising the manuscript so that the novelty in Abidjan is brought out more, however, I would suggest that the authors in the discussion make a more thorough comparison between these two cities, as that is one of their main stated areas of novelty in the introduction/aims. For example, what are the similarities/differences between these cities and what can this tell us about developing air quality monitoring systems in west Africa and policies to mitigate air pollution?

We appreciate the reviewer's suggestion.
Comparisons between Accra and Abidjan have been included throughout the manuscript, with several examples provided in the answers to the questions below. As a general result, our study has identified several similarities between the two cities in terms of PM2.5 pollution levels, including their seasonality, day-to-day variability, and diurnal variation, despite some quantitative differences. However, we observed that differences between various types of sites (urban background, traffic, residential) were more significant than differences between the cities.

B) I previously made the comment that the wording of the title and aims need to be revised so that they do not overstate that this paper provides information on the ‘spatio-temporal variability of’ PM2.5, however the authors do not seem to have made this revision. I reiterate this point as the contribution of this data more appropriately should be the ‘temporal variability of…’ PM2.5 in these two cities. Having 4 sites in Accra and 5 in Abidjan, and often not all of the results across the 9 sites are presented, cannot justifiably give you information on spatial variability. By using that type of phrasing, it is misrepresenting the information that this data can provide.

We thank the reviewer for these further comments and clarifications, which have helped us improve the manuscript.
Title: At the strong recommendation of reviewer 2, the title of the article was reformulated as follows:
Temporal Variability and Regional Influences of PM2.5 in the West African Cities of Abidjan (Côte d'Ivoire) and Accra (Ghana)

Other comments
Paper could benefit from grammatical editing and refinement. There is a lot of text in the Results section that could benefit from condensing for brevity. Alternately, authors can also move some of this text over to the supplemental materials.

Several rewordings have been made throughout the manuscript to better synthesize certain parts and keep the coherency of the paper. They are highlighted in the last version of the manuscript.

1. Fig 5 - Interesting that the peaks between 5am – 8am at Atomic Interchange which is a traffic influenced site has the same PM2.5 levels as the site at the University of Ghana, which should reflect low background levels. Why do you think that is the case and can you provide comment in the discussion section?.

Page 10, Section 3.1: The University of Ghana Lagoon and the Atomic Interchange junction sites are approximately 2.7 km apart. Emissions from traffic and other sources throughout the city not only affect traffic, but also urban background sites. Although the University of Ghana is classified as a background site, its proximity to nearby traffic including university employees, combined with boundary layer dynamics and local meteorology can lead to higher local PM2.5 as it does at the traffic junction. To confirm this hypothesis, a comprehensive analysis of wind direction variations and local traffic patterns is necessary, which could be investigated in future work.

The following comment has been added in the section 3.1
The University of Ghana Lagoon and the Atomic Interchange junction sites are approximately 2.7 km apart. Emissions from traffic and other sources throughout the city not only affect traffic, but also urban background sites. Although the University of Ghana is classified as a background site, its proximity to nearby traffic including university employees, combined with boundary layer dynamics and local meteorology can lead to higher local PM2.5 as it does at the traffic junction. To confirm this hypothesis, a comprehensive analysis of wind direction variations and local traffic patterns is necessary, which could be investigated in future work.

2. In the introduction you make the claim that there has been a lot of personal exposure studies in Accra, but limited field measurements because there is limited availability of equipment and its expensive. Though how would this argument also not apply to personal exposure data collection, which others argue is even more expensive, time-consuming and difficult to do?

Page 2, Introduction: References to personal exposure studies not relevant to our work have been removed from the manuscript.

3. I don’t think you need to provide the formula for the IQR in the results which is a fairly well-known statistical summary measure. If you want to keep it, I suggest moving to the supplementary materials.

Page 11, Section 3.2: As recommended by reviewer 2, equations 6 and 7, which presented the IQR and IQRr interquartile range statistical formulae, have been removed from the manuscript.

4. Authors say they collected measurements at 9 sites (4 in Accra, and 5 in Abidjan) but often results from only 6 sites are presented (in text, figures (Fig 6, Fig 7a, Fig 7b, Fig 8, Fig 9, and tables (Table 2)). Can authors clarify and make clear in the paper that the majority of data presented in many cases is actually only from 6 sites (not 9) (and in the abstract if applicable)?

Page 12, Section 3.2: Our study included data from 9 sites, 4 in Accra and 5 in Abidjan. Daily variation analysis was performed at all nine sites. However, for the seasonal and annual assessments, we focused on the 6 sites where measurements were taken simultaneously over the same period in both cities, as explained in the introduction to section 3.2. This clarification has been highlighted in the latest version of the paper.
This is illustrated by the following sentence in section 3.2.
“To allow for easy comparisons between sites, this analysis is based on data collected over the period between March 2020 and March 2021 when the majority of sites were simultaneously instrumented. Daily average concentrations and their distribution were calculated from hourly average concentrations. The database summarized in Table 2 consists of 360, 343, 324 days of daily average PM2.5 obtained at ACH, UFHB, USEAB in Abidjan and 359, 366 and 248 days of daily PM2.5 in AI, USEAC, KTPC in Accra, respectively.”

5. Page 11 in the result (as well as in the discussion), the authors make comparisons between each day of measurements (i.e., % of days above guideline) with the WHO guideline, however, the guideline is meant to be an annual average, so it would be more appropriate to take the average or median at each site and compare that with the guideline.

Page 11, Section 3.1: The daily concentrations measured were compared to the daily averages recommended by the World Health Organization (WHO). (WHO), specifically 15 µg.m-3 /24h AQG 2021 and 25µg.m-3/24h AQG 2005. Not with the annual averages.
Please note that comparisons with annual averages have been made in section 3.5: Annual Average of PM2.5 in West Africa.

6. Fig 13 is blurry, can the resolution be improved?
Page 21, Figure 13: Resolution of Figure 13 has been improved.

7. I previously made the comment to compare this paper's results in Accra to previous work done by Alli et al (2021) as many of the descriptive analyses are the exact same (albeit data collected in slightly different time periods and number of sites), however the authors did not address my comment with a response or by editing the manuscript.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227509/pdf/erl_16_7_074013.pdf

Page 20, Section 3.5: In our study, the mean annual concentrations recorded at different monitoring sites in Accra between February 2020 and March 2021 ranged from 21.1 µg.m-3 to 24.8 µg.m-3. These levels are slightly lower than those reported by Alli et al. (2021) between April 2019 and June 2020, which ranged from 26 µg.m-3 to 43 µg.m-3. In addition, this study by Alli et al.2021 showed a notable 50% decrease in annual concentration levels compared to measurements taken between 2006 and 2007, which ranged from 37 µg.m-3 to 71 µg.m-3. This confirms a consistent downward trend in PM2.5 levels following the implementation of abatement measures. However, levels are still higher than the WHO annual threshold. Our research in Accra yielded similar results to Alli's, particularly with regard to high concentrations during the dry season, influenced by the harmattan flow.
Following statement have been added in section 3.5
“In our study, the mean annual concentrations recorded at different monitoring sites in Accra between February 2020 and March 2021 ranged from 21.1 µg.m-3 to 24.8 µg.m-3. These levels are slightly lower than those reported by Alli et al. (2021) between April 2019 and June 2020, which ranged from 26 µg.m-3 to 43 µg.m-3. In addition, this study by Alli et al.2021 showed a notable 50% decrease in annual concentration levels compared to measurements taken between 2006 and 2007, which ranged from 37 µg.m-3 to 71 µg.m-3. This confirms a consistent downward trend in PM2.5 levels following the implementation of abatement measures. However, levels are still higher than the WHO annual threshold. Our research in Accra yielded similar results to Alli's, particularly with regard to high concentrations during the dry season, influenced by the harmattan flow.”

8. This sentence in the Discussion (Page 21) does not mean much without context on how large/extensive these 7 studies are, and I would argue that Accra already has some of the more thorough and largest studies characterising air quality in SSA. ‘....The small number of studies (only 7 publications) and these large values clearly warrants for further long-term measurements.

Page 21, Conclusion: The sentence “‘....The small number of studies (only 7 publications) and these large values clearly warrants for further long-term measurements” has been removed and the statement has been modified to reflect your suggestion as follows in the conclusion.
“Accra has been extensively studied to characterize its air quality, while Abidjan lacked comparable research in this area. As a general result, our study has then allowed pointing out various similarities between both cities in terms of PM2.5 pollution levels, their seasonality, day to day variability, and diurnal variation, even if quantitative differences occur. Nevertheless, we found that differences between different types of sites (urban background, traffic, residential) were larger than differences between the cities. In addition, More long-term studies are urgently needed to improve the understanding of air quality in both cities, especially in Abidjan. In particular, such measurements would allow tracking the impact of growing urbanization in both cities on air quality.”

9. My previous comment about the potential impact of the COVID pandemic was not related to carrying out maintenance on the equipment but how changes in urban activities and transport during this time (i.e., less people leaving their homes) may have impacted the air pollution results of this paper. I would suggest adding this into your discussion section.
We thank the reviewer for the clarification and suggestion. Accra experienced a partial shutdown for less than a month starting on March 30, 2020 with restrictions lifted on April 20, 2020. Similarly, in Abidjan, the restrictions had a negligible impact on traffic or human movement around the instrumented sites.
Understanding COVID-related changes to air pollution would require significant effort (consideration of annual variability in meteorology and other human activities beyond just traffic). Given the limited duration of movement restrictions in these two cities, we have not considered COVID shutdowns separately in this manuscript.

10. In the abstract you don’t need to say how the study was funded. I would suggest removing the phrase ‘…funded by the Make Our Planet Great Again (MOPGA) program’.

Page 1, Abstract: This statement has been removed from the final version of the Abstract.

18-Mar-2024

Dear Dr Bahino:

Manuscript ID: EA-ART-01-2024-000012.R1
TITLE: Temporal Variability and Regional Influences of PM2.5 in the West African Cities of Abidjan (Côte d'Ivoire) and Accra (Ghana)

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Reviewer 2

Many thanks to the authors for addressing my second round of comments