the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jan 2024
The annual cycle and sources of relevant aerosol precursor vapors in the central Arctic
Abstract. In this study, we present and analyze the first continuous timeseries of relevant aerosol precursor vapors from the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. These precursor vapors include sulfuric acid (SA), methanesulfonic acid (MSA), and iodic acid (IA). We use FLEXPART simulations, inverse modeling, sulfur dioxide (SO2) mixing ratios, and chlorophyll-a (chl-a) observations to interpret the 20 seasonal variability of the vapor concentrations and identify dominant sources. Our results show that both natural and anthropogenic sources are relevant for the concentrations of SA in the Arctic, but anthropogenic sources associated with Arctic haze are the most prevalent. MSA concentrations are an order of magnitude higher during polar day than during polar night due to seasonal changes in biological activity. Peak MSA concentrations were observed in May, which corresponds with the timing of the annual peak in chl-a concentrations north of 75° N. IA concentrations exhibit two distinct peaks during 25 the year: a dominant peak in spring and a secondary peak in autumn, suggesting that seasonal IA concentrations depend on both solar radiation and sea ice conditions. In general, the seasonal cycles of SA, MSA, and IA in the central Arctic Ocean are related to sea ice conditions, and we expect that changes in the Arctic environment will affect the concentrations of these vapors in the future. The magnitude of these changes and the subsequent influence on aerosol processes remains uncertain, highlighting the need for continued observations of these precursor vapors in the Arctic.
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RC1: 'Comment on egusphere-2023-2953', Anonymous Referee #1, 07 Feb 2024
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Comments to the muanuscript egusphere-2023-2953
Boyer et al. The annual cycle and sources of relevant aerosol precursor vapors in the central Arctic.
Reviewer's comments
The article presents and analyzes the first time series of aerosol precursor vapors (sulfuric acid (SA), methanesulfonic acid (MSA), and iodic acid (IA)) that are relevant to the central Arctic during MOSAiC. The authors conducted the measurements with state-of-the-art instruments, and the results are crucial in assessing the impact of anthropogenic emissions in the Arctic. The article is well structured, and well written, and only requires minor corrections before acceptance.
Minor comments
- The article discusses the crucial findings related to the concentration of atmospheric gases in the Arctic. However, the information is not presented in a concise format such as a table, which would enable the reader to easily examine the data. It is recommended to include a table that displays the monthly and seasonal averages of the primary anthropogenic pollutants.
- The date in Figure 4 is confusing. It is recommended to improve the date and use a single format.
- Figure 1 presents the gas phase time series for SA, MSA, and IA during clean and polluted periods using a violin-type scheme. This type of schematic can be a bit confusing. It is recommended to present the information in another format, for example, box-and-whisker diagrams. Could you expand the description of these results? Perhaps showing a table with the main statistical results.
- Figure 2c shows several results that are difficult to interpret. Is it possible that you could improve or present these results in another format?
- The message describing Figure 2c mentions the dashed white line denoting the monthly median latitude of Polarstern during the campaign. However, in Figure 2c no dotted line is shown. The only one observed is a continuous white line.
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RC2: 'Comment on egusphere-2023-2953', Anonymous Referee #2, 11 Apr 2024
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Boyer et al. describe one year of relevant aerosol precursor in the gas phase from the central Arctic during the MOSAiC expedition from Sep 2019 to Oct 2020. The data include sulfuric acid (SA), methanesulfonic acid (MSA), and iodic acid (IA). They used the FLEXPART simulations, inverse modeling, and satellite chlorophyll-a (chl-a) to interpret the seasonal variability of the studied parameters and identify their source regions. The results conclude that natural and anthropogenic sources contribute to different aerosol types depending on the season, biotic and abiotic factors, and air mass movement. The information provided and the study's conclusions could be helpful to the scientific community. The manuscript does, however, require more explanation in some sections. The results visualizations, as I explain below, are my major concern.
General comments:
Section 2.6, Line 207: The FLEXPART and inverse modeling need further explanation on how they work. For instance, what are the frequency, timing and length of back-trajectories used? Where do the main sources of air mass dominate during the measurement period? A figure showing the air mass back-trajectories in the supplement would be beneficial. While ECLIPSE is a fundamental tool in presenting the results, no details on how It works, references and previous applications.
The conclusion section is long and has discussion sentences/cited references that might be moved to Results and Discussions. The Section shall summarize the major findings along with their implications.
Specific comments:
Line 94: Between brackets, define the HOx, for example, (OH and H2O).
Line 97: At least define what IxOy refers to at the 1st mention.
Figure 1: The data is misleading and the word “time series” in the caption is not appropriate. From the 1st glance, the readers may interpret that the colors distinguish between the input from biogenic (clean) and anthropogenic (polluted) sources. While I see the polluted cases represent the excess concentration to the biogenic one (polluted + biogenic). Indeed, I think this figure after a suitable explanation could be transferred to the supplementary material since it doesn’t contribute to the main conclusion of the study.
Line 178: A statistical test would be more robust to evaluate that there is no significant difference in medians.
Line 200: Not only cloudiness but also the low-incidence sun angle in winter hinders the measurement of chl-a from satellites at high latitudes.
Line 270: do you think the word “diurnal” fits the explanation here? Diurnal means 24-hour variations from day to night.
Figure 2: I don’t see the advantage of adding the 5-minute time resolution data in the background. The figure presents the annual cycle, so the monthly median with the shaded area or monthly box charts that describe the whole statistics is enough. Panel-A: the left y-axis is hidden. Panel C: It is better to present the missing data in chl-a as blank (white) to differentiate low values and non-measured times. Accordingly, the dotted white line must be modified.
Figure 3: Same comment as Figure 2. Presenting a time average (median) may be better to highlight the main variations throughout the time series.
Figure 4: The presentation of the data is hard to interpret. For example, the oceanic contribution in July is about 0.1 µg/m3 or (0.18 – 0.1 µg/m3). Indeed, I see Fig. S8 is worth presenting in the main manuscript rather that Fig. 4.
Figures 5, 6, and 7: In my view, the colors show the contribution of each polygon, which, when added together, gives the concentration overall.
Line 375: Refer to the polygon number.
Line 420: Citing Park et al. is not enough here because it handles the DMS rather than MSA. There are studies in the literature that have reported the link between marine biological activity and aerosol chemical composition (or MSA) in different marine environments (e.g., North Atlantic, Mediterranean and Eastern China Seas).
Line 443: Introducing an equation or more explanation on the influence index calculation and the unit used is required to make it clearer.
Line 447: It is worth highlighting that DMS emissions are mostly related to senescent phytoplankton cells rather than healthy cells.
Line 723: Who is MDO? What is the role of BH?
Typos:
Line 52: “product” instead of “byproduct”
Line 60: “sulfur” instead of “sulfate”
Line 151: -50% to …
Line 255: remove “or”
Citation: https://doi.org/10.5194/egusphere-2023-2953-RC2 -
RC3: 'Comment on egusphere-2023-2953', Anonymous Referee #3, 15 Apr 2024
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The manuscript presents very interesting and useful data. It is well organized and clearly written and the elaborations and conclusions are scientifically sound. I recommend publication once the following minor issues are addressed.
Sect. 2.3. This Paragraph deals with a key issue that should be addressed more quantitatively. For the provided plots it is quite evident that pollution from the ship or ongoing surrounding activities did not spoil the measurements, nevertheless the differences should be presented more quantitatively: a statistics test should be employed to demonstrate that the data distribution are not statistically different between the “clean” and “polluted” data subsets. Furthermore, I find interesting the fact that, judging from Figure 1, MSA is more affected from pollution than SA (the difference between the “clean” and “polluted” medians is higher for the MSA case than for SA): have the authors an explanations for this? Which activity can be a source of MSA?
Sect. 2.5. Which time resolution have the CHL data?
Sect. 2.6. Please provide more information on the back trajectories: time resolution, length, frequency. Moreover, was the travelling height of the back-trajectories taken into consideration for the elaborations?
L265. Why “including SA, MSA, and IA”? Fig. 2a presents precisely SA, MSA and IA.
L280. No “dotted white line” is present in Figure 2c.
L317. “To further evaluate the sources of SO2 and SA in our measurements, we examined emissions of anthropogenic sulfate…”. I do not think this expression to be correct: by coupling the ECLIPSE v6b with flexpart trajectories the authors are not evaluating the emissions. Please reformulate the sentence.
L371. “Despite lower anthropogenic SO4-S influence from the North Asia sector during March and April”: refer to the appropriate Figure here, for major clarity.
L640. Correct in “sea-ice continues to decline”.
Citation: https://doi.org/10.5194/egusphere-2023-2953-RC3
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