the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Oct 2026
Three Pathways of Eastward Transport of North African Dust: Synoptic Patterns and Impacts on Air Quality in China
Abstract. The long-range eastward transport of North African dust substantially influences China's climate, environment, and human health. However, the circulation mechanisms that modulate its pathway variability and downstream impacts remain poorly understood. In this study, we investigated the synoptic patterns along three distinct eastward transport pathways of North African dust and their impacts on air quality in China using reanalysis and observations. Results show that seasonal variations in dust activity and the position of the westerly belt govern the eastward transport of North African dust, with transport peaking in April and spring accounting for 56.3 % of the annual dust mass potentially available for eastward transport. Among the three transport pathways, the northern pathway transports dust northward into Europe, followed by eastward advection through the mid- and high-latitude westerlies following pre-trough uplift. In contrast, the middle pathway features Mediterranean uplift and northeastward deflection. Mid-latitude westerly transport is modulated by western Mediterranean cyclonic activity, a southward-extending trough, and the blocking and splitting effects of the European high-pressure system. The southern pathway transports dust eastward along lower latitudes and around the southern Tibetan Plateau toward southern China. This pathway is guided by southward displaced lower-latitude westerlies, the European cold trough, and Himalayan topographic deflection. These dust plumes produce maximum PM2.5 anomalies of 54.1–202.4 μgm-3 decreasing from north to south across China. These findings may support early warnings of the eastward transport of North African dust to East Asia—an overlooked issue that is becoming increasingly critical as aerosol levels decline in China.
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Status: open (until 24 Nov 2026)
- RC1: 'Comment on egusphere-2026-5002', Anonymous Referee #1, 27 Oct 2026 reply
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RC2: 'Comment on egusphere-2026-5002', Anonymous Referee #2, 02 Nov 2026
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This manuscript investigates the seasonal characteristics of eastward North African dust transport and examines three transport pathways toward East Asia using MERRA-2 and ERA5 reanalysis data, HYSPLIT trajectory simulations, and satellite and ground-based observations. The three case studies provide detailed synoptic analyses. However, some conclusions require stronger quantitative support, particularly regarding the representativeness of the three transport pathways and the attribution of near-surface PM anomalies in China to North African dust transport. I therefore recommend a major revision as follows:
- Section 2.3 and 4. The authors use a PM10 threshold of 500 to exclude the influence of local or nearby dust sources, citing Zhou et al. (2023a). However, Zhou et al. (2023a) used this threshold to classify dust weather conditions based on UAV observations over the Taklimakan Desert, rather than to distinguish dust originating from different sources. Therefore, this threshold alone cannot reliably exclude contributions from other East Asian dust sources. Although the HYSPLIT simulations and lidar observations support the long-range transport of North African dust to East Asia, they do not demonstrate that these elevated dust plumes contributed to the observed surface PM anomalies. In Section 4, the authors further attribute the near-surface impacts mainly to the deposition of fine particles from elevated dust plumes around lines 520: “This indicates that the near surface environmental impact of eastward transported North African dust over East Asia mainly results from the deposition of fine particles from the elevated dust plume. In three cases, the dust plumes did not show pronounced intrusion into the planetary boundary layer”. However, no deposition fluxes or direct evidence of this process are provided. The authors should provide stronger evidence linking North African dust transport to surface PM10 and PM2.5 anomalies, or revise their conclusions regarding its impacts on air quality in China.
- Section 3.2. The manuscript identifies three representative transport pathways based on three case studies, but provides no long-term statistics to establish their relative occurrence frequencies during 2006-2023. In particular, the statement around Line 495 that “In reality, most North African dust is transported toward the Indian Ocean or the Arabian Peninsula, and seldom crosses mountains and plateaus to affect southern China. Therefore, the southern transport pathway is relatively rare” is not sufficiently supported by the three selected case studies. Please provide statistical evidence for these conclusions or revise them accordingly.
- Section 3.1. The analysis of the spatial distribution and seasonal variability of North African dust relies primarily on MERRA-2 dust data, which have inherent uncertainties. The authors should compare the key results with other available datasets, such as CAMS DOD or other reliable satellite-derived dust products, to evaluate their consistency and assess the robustness of the conclusions.
- Section 2.3 (around Line 190). The Methods section states that “The monthly background concentrations averaged over the past three years were subtracted from the original PM10 and PM2.5 concentrations to obtain anomaly disturbances for impact assessment.” However, the caption of Fig. 11 states that “The anomaly background fields are defined as the averages of the monthly mean PM10 and PM2.5 concentrations for the event year and the preceding and following years.” These two reference periods do not match. Please clarify which reference period was actually used in the calculations and correct the inconsistent descriptions.
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- 1
This manuscript investigates three distinct pathways of eastward transport of North African dust and their associated synoptic circulation patterns and impacts on air quality in China. The topic is scientifically relevant, and the combination of reanalysis datasets, lidar observations, and trajectory simulations provides useful insights into intercontinental dust transport. The work is well-structured. However, there are areas that require clarification and improvement to enhance understanding. I recommend that the manuscript be considered for publication after addressing the comments mentioned above.
Comments
2.In the discussion of the middle pathway (Page 16, Fig. 7), the authors argue that the high-geopotential-height ridge extending from western to central Europe partially blocked and split the midlatitude westerlies. However, Fig. 7 only presents the circulation pattern at 12:00 UTC on 18 March 2022. A single snapshot is insufficient to demonstrate the persistence of this circulation configuration or its evolving influence on the westerly flow. I recommend including the temporal evolution of 500 hPa geopotential height and horizontal winds, preferably in the Supplement. If the authors intend to characterize this circulation as a formal atmospheric blocking event, an objective blocking criterion and the event duration should be provided. Otherwise, I suggest using more cautious wording, such as "the high-pressure ridge modified the regional configuration of the midlatitude westerlies," rather than implying a well-established blocking mechanism.
3.In the discussion of the southern pathway (Lines 465-470 and 488-490), although topographic effects are likely important in this case, the current figures do not provide sufficient evidence to isolate the influence of the Himalayas from that of the background atmospheric circulation. I suggest that the authors provide additional vertical cross-sections along the southern margin of the Tibetan Plateau. Such information would strengthen the physical interpretation of the southern transport pathway.
4.The potential impacts of North African dust on air quality in China are scientifically interesting, and the use of multi-site lidar observations provides valuable evidence of long-range dust transport. However, the attribution of the observed surface PM anomalies to North African dust remains uncertain. In particular, for the middle pathway, the authors report that the transported dust is mainly distributed at altitudes of approximately 5-8 km over Dunhuang, whereas substantial positive PM2.5 anomalies are observed in parts of central and northern China. It remains unclear how, when, and through which physical processes the elevated dust plumes could contribute to the observed surface PM2.5 enhancements. I suggest that the authors provide a more detailed discussion of the possible mechanisms connecting elevated dust transport to surface PM variations. In the Abstract and Conclusions. I recommend explicitly stating that the reported PM values represent observed concentration anomalies during the transport events rather than quantitatively attributed contributions from North African dust.
6.Section 2.4 provides limited information on the specific trajectory configurations, which makes it difficult to reproduce the results. I recommend that the authors explicitly report the meteorological dataset used to drive HYSPLIT, the starting locations and altitudes, release times, trajectory durations, vertical motion calculation method, and number of trajectories.
7.For middle pathway case, on Page 16, the authors argue “the mid-latitude circulation was influenced by the ridge over North Africa and the western Mediterranean...”. However, the Conclusions emphasis “cyclonic activity over the eastern Mediterranean resulted in ...”. A more consistent description of the geographical locations and dynamical roles of these systems would help readers better understand the proposed transport mechanism.
8.The rationale for selecting the three representative dust transport events is not introduced until Section 3.2 (Page 11). Given that the comparison of the northern, middle, and southern pathways is central to the study, I suggest briefly introducing the rationale for this classification and case selection in the Introduction.