the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Aug 2024
Dust storms transport proteinaceous matter from the Gobi Desert to Northern China
Abstract. Dust storms can greatly influence the ecosystem's productivity and biogeochemical nitrogen cycles by providing new nutrients. However, the transport of proteinaceous matter (combined amino acids, CAAs) by dust storms to downwind ecosystems remains unclear. Here, the concentrations and δ15N values of individual CAAs in Gobi surface soil and vegetation, as well as in PM2.5 samples from four cities in Northern China were characterized. Proline dominated the total pool of CAAs in urban PM2.5 during non-dust periods, whereas CAAs transported by Gobi dust were rich in alanine, glycine, and glutamic acid. The concentrations and percentages of these three CAAs in PM2.5 from Northern China notably increased during dust periods. During non-dust periods, the δ15N values of individual CAAs in urban PM2.5 fell within their respective ranges in local urban sources, suggesting CAAs in PM2.5 were primarily influenced by local urban sources during non-dust periods. Compared to their values in urban PM2.5 during non-dust periods, glycine and leucine in Gobi Desert sources exhibited δ15N depletion by more than 6‰. During dust periods, glycine and leucine in urban PM2.5 all exhibited negative shifts in their δ15N values, confirming that Gobi dust is a significant source of CAAs in PM2.5 in Northern China. The dry deposition of protein-N from Gobi dust was calculated using nitrogen isotopic mass balance based on the δ15N values of glycine and leucine, yielding a value of up to 0.36 mg N m-2 d-1. The rapid accumulation of such considerable protein-N quantities may profoundly affect oligotrophic ecosystem productivity.
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RC1: 'Comment on egusphere-2024-2065', Anonymous Referee #1, 02 Oct 2024
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The manuscript addresses an interesting and emerging issue regarding the role of dust storms in aerosol transport, its effect on particulate matter composition, and its role in critical environmental issues such as air quality and ecosystem productivity. Specifically, the authors assessed the contribution of Gobi dust to proteinaceous combined amino acids (CAAs) in PM2.5 across four urban regions in Northern China during dust events. The authors collected data from multiple sites (Beijing, Tianjin, Shijiazhuang, Taiyuan), which allows for a regional comparison of CAAs in PM2.5. Their approach involved analyzing the concentrations and δ15N isotopic signatures of CAAs from both the Gobi desert and local urban sources. Additionally, they quantified the Gobi dust's input to CAAs in PM2.5 and evaluated the dry deposition fluxes of protein-N to explore the biogeochemical impacts. Overall, the rationale for this study is well stated, the experiment is well described, and the work points out important issues that are highly relevant. However, the manuscript needs some improvement.
Major Comments
- The comparison of protein characteristics in PM2.5 from urban environments with those in dust sources lacks a detailed interpretation of its broader implications, being limited only to surface-level comparison. The study could benefit from a more in-depth discussion of the potential biological or chemical mechanisms by which dust-borne CAAs affect the local and regional nitrogen cycle. This could help link the findings to broader environmental implications.
- The sampling period (March 24–31, 2018) represents a short window of time. While the authors acknowledge the occurrence of dust storms during this period, it is unclear if these results are representative of long-term trends or typical dust events. A broader period could strengthen the conclusions, or could the authors provide additional context on whether this period represents typical dust activity for that year or region
- The use of satellite imagery and back-trajectory analysis to confirm Gobi dust as the source is an important strength of the paper. However, additional validation through ground-based measurements or comparison with other dust episodes would confirm that the identified CAA increases were directly attributable to Gobi dust.
- The authors use a fixed dry deposition velocity (Vd) based on previous studies. However, Vd is typically influenced by factors such as particle size, wind speed, and hygroscopicity. The use of a fixed value introduces uncertainty in the estimation of deposition fluxes. A site-specific Vd estimate would improve the accuracy of their calculations.
- The paper focuses heavily on the Gobi dust contribution but does not extensively explore the potential influence of local urban sources of CAAs. It would be helpful to discuss how industrial, vehicular, or other anthropogenic emissions contribute to the CAAs in PM2.5. This would provide a clearer differentiation between dust and urban source contributions. Further justification or consideration of urban δ15N variability is needed.
Minor Comments
- It is suggested that the sampling locations be visually represented on a map and be incorporated into Fig 8 as a subplot. This will provide a clearer spatial understanding of the study's geographic scope.
- The terms dust storm and dust event are used interchangeably throughout the manuscript, but they can be interpreted as two different transport mechanisms in the dust transport field. The author should consistently use one or the
Citation: https://doi.org/10.5194/egusphere-2024-2065-RC1
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