Please find my comments in the attachment.

Review of egusphere-2024-113 by A.C. Aiken

Summary:

This manuscript describes a dust event that occurred in the desert southwestern United States. The data used includes meteorology and particulate matter (PM2.5 and PM10) from a range of available monitoring sites within New Mexico and Texas. The manuscript addresses relevant science questions within the scope of ACP, presenting data from 19 monitoring stations in NM and TX of a dust event that occurred in February 2023 and had the highest PM2.5 concentration recorded in the last 20 years at one of the sites (Lubbock, TX). Overall, the manuscript is well-written and worthy of publication in ACP. A few areas could be improved with minor revisions to highlight the importance of the results as they are presented in the current version to relate this dust event and storm within a larger context in terms of visibility, PM, and their impacts.

The authors’ presentation of the data is well-structured and clear. The scientific impact could be improved by adding additional information in a general sense on how this event relates to others in region as well as the globe in the abstract and conclusion sections. Discussing a regional or seasonal average for visibility and PM versus those during the event would further highlight the magnitude of the different conditions experienced during the event versus the “background”. Some more detail of how averages were calculated and reference periods with no dust events were selected within the methods section would be beneficial. Background conditions with no dust events are of interest and should be presented in the text as well as potentially in a table as the PM concentrations are hard to see in the figures since the event concentrations are so high in comparison. The conclusions section could be expanded as well, and more detailed suggestions are included in the comments below. For example, an interesting area to highlight would be a summary of the mass ratios for PM2.5/PM10 that were analyzed in the results section as well as a comparison of the PM data during the event versus the periods before and after the event to understand the magnitude of the impact on PM (and visibility). More details and recommendations are included below.

General Comments:

Title

• Clearly reflects the contents of the manuscript.

Abstract

• Can you relate in general how this dust event and dust storm relate to others in the region and potentially globally in terms of duration, wind speeds, visibility, and PM concentrations?
• It is highlighted that PM2.5 was the highest ever recorded at the Lubbock site. Could you also add to the abstract what the ratios of PM2.5/PM10 were on average during the event and storm as well as the dust storm in relation to the baseline or background and how this compares to other storms and/or regions?

Introduction

• Line 43: Recommendation to expand this paragraph on how this storm relates to others in the area. It is stated that this storm was “one of the most significant” over the last decade. Could a summary of the other storms be included to understand more of the climatology for the region? Are there other references to include to show historical comparisons for this area? Include how often they occur and last as well as available summaries/measurements of PM.
• Is there a seasonality for the region and/or known occurrence in the area due to different meteorological patterns or events? There is some information on this provided in the results/paragraph Line 186 but adding a higher-level summary in the introduction would help the reader put this study within a larger context before getting into more of the details in the results section.

Methods

• Add details of how the average daily values for PM were calculated. Was the dust event excluded or included and why? How much would those averages change if you did the opposite?
• If the dust event was included in the daily averages should the day before and after be included to assess how much the daily average changed during the day of the event?
• When concentration ratios are calculated for the event versus the period before – how was the period before defined? How would it compare to an average after the event – do the concentrations return to the previous values or is there a significant difference or lag in time before the values return to the pre-event concentrations?
• Would it be possible to look at a longer background period such as a week or a month to establish a “background” for the data?

Results

• Would it be possible to calculate background values for visibility and PM over a longer time period and to discuss what those values are for a month or the season?
  • It looks like visibility may be more stable than PM, but it’s not easy to tell from the figures in the main text what a non-dust period looks like in terms of PM.
  • If a month is too long, even a week would show a longer period to give an idea of PM and ratios between the size cuts for the region. Ideally, you could look at all the station averages as well as an average for all the data presented. For example, there look to be two main areas where the sites have both PM10 and PM2.5. How similar/different are the concentrations and ratios at those two sites and what might be the reasons for those differences that warrant further investigation.
• Could you add a table to the main text that shows the background values for visibility and PM versus the event average and the peak during the event?
• Consider moving the figures within S4 that contain the difference and ratios between PM10 and PM2.5 into the main text and expanding the discussion.
  • Would it be possible to extend the PM2.5/PM10 ratio figure beyond the day of the event to look at that ratio in a broader context?
  • Are the range of values that are all < 0.6 representative of region during no dust events or just the hours before the event as shown?

Conclusion

• It’s very interesting that the PM2.5 fraction is so low during the event, much lower than dust events in other areas. This should be mentioned here as well as in the results.
  • Is it known if this is a regional signature or is this not well-characterized since most sites don’t have PM10 and PM2.5?
  • What might the implications be to human health, atmospheric transport and potentially climate for dust events like these versus those that have a higher PM2.5/PM10 ratio – or – is there so much total mass that the PM2.5 fraction is not to be overlooked? How do the storms referenced in the results with ratios > 0.6 relate to this storm in terms of PM concentrations?
• If a lot is not known about what meteorological conditions and seasons result in observed dust events and storms for this region, perhaps the conclusions should include a future work section that discusses what is known versus what needs more research, and whether this can be done with the existing observations or what might improve data collections to further the state-of-the-science for the scientific community to understand dust events in the southwestern US as they are now and might change in the future.

Specific comments:

Lines 151 and 334: Was the period “16 hours” or 18 that was stated in the abstract?

Line 274: type-o - replace “tru exsposure” with “true exposure”

Tables S3 and S4 – State in the table header or footer what the bold data signifies.