Seasonal and diurnal variability in O<sub>3</sub>, black carbon, and CO measured  at the Rwanda Climate Observatory

DeWitt, H. Langley; Gasore, Jimmy; Rupakheti, Maheswar; Potter, Katherine E.; Prinn, Ronald G.; Ndikubwimana, Jean de Dieu; Nkusi, Julius; Safari, Bonfils

doi:https://doi.org/10.5194/acp-19-2063-2019

Articles | Volume 19, issue 3

https://doi.org/10.5194/acp-19-2063-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-19-2063-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 3

Research article

|

14 Feb 2019

Research article |

| 14 Feb 2019

Seasonal and diurnal variability in O₃, black carbon, and CO measured at the Rwanda Climate Observatory

H. Langley DeWitt, Jimmy Gasore, Maheswar Rupakheti, Katherine E. Potter, Ronald G. Prinn, Jean de Dieu Ndikubwimana, Julius Nkusi, and Bonfils Safari

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Final revised paper (published on 14 Feb 2019)
Preprint (discussion started on 02 Feb 2018)

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Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of DeWitt et al. - Rwanda Climate Observatory', Anonymous Referee #1, 02 Mar 2018
RC2: 'Review DeWitt et al.', Anonymous Referee #2, 07 Mar 2018
AC1: 'author comments', H.L. DeWitt, 30 Jun 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by H.L. DeWitt on behalf of the Authors (28 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (14 Aug 2018) by Rupert Holzinger

RR by Anonymous Referee #1 (28 Aug 2018)

RR by Anonymous Referee #2 (02 Sep 2018)

Suggestions for revision or reasons for rejection

The authors have done a very good job of improving the flow of the manuscript. As I stated in my original review, this is an important dataset in an area with few measurements and thus adds important new information. I do believe the authors have improved the manuscript and would recommend for acceptance after a few minor comments are addressed to improve clarity.

Line 24, I would recommend adding either regional or local to this sentence to improve clarity, “…which coincide with the two (regional or local?) biomass burning seasons.”

Line 55, The southern Africa burning season is more than just JJA, but extends until October in southern regions (austral spring). This can be seen in Figure 5 and previous literature.

Line 83, these data are not data about climate change really, but are of SLCP. This is similar for line 581. These measurements are not of impact of climate change really. I would recommend removing that or explaining the linkages better.

Line 96, this sentence is incomplete. I believe it should be “Rwanda has…”

Line 198 what is spatial resolution of NCEP reanalysis used?

Line 290, I believe this should be figure 8

Lines 315-353, this analysis is really interesting. It is inconclusive at the end, but as described in conclusions line 531, points to some research needs. I would recommend that the authors add a sentence or two summarizing this assessment and clarifying that there is still uncertainty of where this high fossil fuel comes from or if it is not being calculated correctly as info is not for local conditions before beginning section 3.3. Reading through I felt it changed abruptly. This inconclusiveness is an interesting and relevant finding and I believe should be highlighted.

Line 379, which estimates are you referring to here? Are these estimates for this area in particular? Or similar areas?

Line 381, I do not believe that your results show that targeting local emissions could bring measureable decreases in ambient PM or resultant impacts. Your local BC is estimated to be ~1ug/m3. Obviously there are associated PM and PM precursor emissions related to the BC emissions that account for the 1ug/m3, but how much? That last part isn’t known as there aren’t PM measurements – and thus I think jumping from BC to PM to health impacts is too strong of a statement. I would recommend removing or altering this statement.

Line 400, in order to see the peak in evening emissions in local cooking/generators, the station would have to be within the boundary layer generally. However, Line 389 suggests that ozone peak in evening is from transport above the boundary layer. This is confusing to me. It does appear that ozone is high starting ~20:00 and BC ~19:00. It could be possible that this hour is enough for the station to change from being within the boundary layer to out of it. If this is the case, then I would recommend in this section adding the times that the pollutants peak to clarify “evening”.

Line 414, I would recommend adding the exact dates of the case studies when they are first mentioned here.

Line 424, it seems the peaks in BC in May are all in the morning during cooking times, yet on average (from fig 8) the peak is seen in the evening. I found that interesting. I would recommend adding more time ticks to the legend of this figure. Trying to look for cooking times (which I assume are 6-8am and 6-8pm) it is hard to see without more ticks. Also, I would recommend that the labels of all graphs with time on x-axis are labelled and indicate the convention used (month/day/year) in order to avoid confusion.

Line 439, I would recommend that the authors add a sentence or two to transition from BC to PM here. Also, I would recommend subscripting 2.5 In PM2.5.

Line 462, as mentioned in previous reviews, the peak seen in Hersey et al (2015) is not due biomass burning. The peak is due to local emissions during winter, which in many sites is from domestic burning. South Africa is impacted by biomass burning more in Aug-Oct (see e.g. SAFARI aerosol papers, Queface et al, 2011; Tesfaye et al, JGR, 2011; Horowitz et al. ACP, 2017, etc.).

Line 467, PM3.5 should be PM2.5. Line 482, there was a SAFARI2000 campaign as well, which was larger. I don’t think it would change the conclusions here, just that there have been more recent measurements from SAFARI than in 1993 (line 486).

Figure 3, I would recommend adding more labels to the ticks as it is difficult to eye-ball the 3-month dry and wet seasons with other two labels. This makes it more difficult for the reader to easily pick out the differences.

Figure 12, I would not include the daily WHO recommendations on monthly averages of data as these are two different averaging times. I think this point needs more context in explaining the differences and should be in the text only.

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ED: Reconsider after major revisions (11 Sep 2018) by Rupert Holzinger

AR by H.L. DeWitt on behalf of the Authors (04 Dec 2018) Author's response Manuscript

ED: Publish as is (13 Dec 2018) by Rupert Holzinger

AR by H.L. DeWitt on behalf of the Authors (22 Dec 2018)

Short summary

Air quality in rapidly developing East Africa is a growing but understudied concern. We analyzed long-term black carbon, carbon monoxide, and ozone measurements from the remote Rwanda Climate Observatory and found that seasonal regional biomass burning raised black carbon levels to above-urban concentrations 6 months out of the year. Additional local pollution could exacerbate this issue. More regional monitoring needs to be done to understand and reduce air pollution in this region.

Seasonal and diurnal variability in O3, black carbon, and CO measured at the Rwanda Climate Observatory

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Seasonal and diurnal variability in O₃, black carbon, and CO measured at the Rwanda Climate Observatory