تحلیل زمانی منشأ گردوغبارهای فرا منطقه‌ای استان گلستان با استفاده از مدل NOAA HYSPLIT (در بازه 21 تا 25 شهریور 1404)

Objectives
It was the objective of this study to identify the temporal origin and transport pathways of extra-regional dust storms affecting Golestan Province in northeastern Iran, during the period 12–16 September 2025. For this purpose, the NOAA HYSPLIT backward trajectory model and the Sentinel-5P satellite observations were integrated to determine dust source regions, transport dynamics, and atmospheric conditions at different temporal scales (12, 24, and 72 hours). In addition, the study endeavored to evaluate the aerosol layer height and the Absorbing Aerosol Index (AAI) to verify dust occurrence and assess its spatial distribution. Satellite-derived information was further validated using ground-based PM₁₀, PM_2.5, and horizontal visibility measurements. The findings help yield a deeper understanding of the transboundary dust transport from Central Asia to northern Iran and provide scientific evidence to support air quality management, environmental monitoring, and developing early warning systems for dust-related hazards in Golestan Province.
Material and Methods
An integrated remote sensing and atmospheric trajectory analysis approach was employed to investigate the origin and transport pathways of extra-regional dust events affecting Golestan Province, in northeastern Iran, during the above-mentioned study period. Backward air-mass trajectories were simulated using the NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model together with GDAS meteorological data. Trajectories were calculated for 12, 24, and 72-hour intervals at an arrival height of 100 m above ground level to identify potential dust source regions and atmospheric transport routes. Satellite observations from the Sentinel-5P platform were used to characterize aerosol conditions during the study period. Aerosol Layer Height (ALH) products were analyzed to determine the vertical distribution of aerosol plumes while the Absorbing Aerosol Index (AAI) was employed both to detect UV-absorbing aerosols associated with mineral dust and to evaluate their spatial extent and intensity. The combined interpretation of HYSPLIT trajectories and satellite-derived aerosol products allowed not only the probable dust source regions but also the long-range transport mechanisms to be identified. To validate the remote sensing and trajectory modeling results, use was made of the ground-based meteorological and air quality observations collected from the synoptic stations in Golestan Province. Daily PM₁₀ and PM_2.5 concentrations together with horizontal visibility records were analyzed to confirm the occurrence and severity of dust events. Finally, spatial and temporal comparisons were performed among the trajectory outputs, satellite observations, and surface measurements to evaluate the consistency of the results and to improve the reliability of dust source identification and transport pathway analysis.
Results
The integrated analysis of HYSPLIT backward trajectories, Sentinel-5P satellite observations, and ground-based measurements revealed the occurrence of significant extra-regional dust events over Golestan Province during the study period. The 72-hour backward trajectory analysis indicated that the principal dust air masses originated from Central Asia, particularly Kazakhstan, Uzbekistan, and Turkmenistan, and were transported toward northeastern Iran by the prevailing northeasterly atmospheric circulation. Trajectories at higher altitudes (2–4 km) suggested that part of the dust transport occurred within the middle troposphere before descending over the study area. The 24-hour trajectory analysis demonstrated that shorter-range transports were dominated by air masses moving from the Caspian Sea region and southern Caucasus, whereas the 12-hour trajectories indicated that local and regional winds from Turkmen Sahara and northern Khorasan contributed to near-surface dust accumulation. These findings suggest that the observed events resulted from the combined influence of long-range transboundary transport and local atmospheric circulation. Sentinel-5P Aerosol Layer Height (ALH) products showed elevated aerosol layers over eastern Iran and Turkmenistan prior to the event, supporting the hypothesis of long-distance aerosol transport. Moreover, the Absorbing Aerosol Index (AAI) identified high aerosol concentrations over eastern Caspian coastal areas and Golestan Province, with values indicating intense mineral dust loading. Spatial correspondence between satellite observations and model trajectories confirmed Central Asia as the dominant source region od dust air masses. Ground observations further validated these findings as evidenced by the PM₁₀ concentrations reaching approximately 110 μg m⁻³ on 15 September 2025 accompanied by a substantial reduction in horizontal visibility, all of which confirm severe dust conditions. The consistency observed among trajectory simulations, satellite-derived aerosol products, and surface observations demonstrates the reliability of the integrated methodology proposed herein for identifying dust sources and transport pathways affecting Golestan Province.
Conclusion
The results of the present study demonstrated the effectiveness of integrating the NOAA HYSPLIT trajectory model, Sentinel-5P satellite observations, and ground-based air quality measurements in identifying the origin and transport pathways of extra-regional dust events affecting Golestan Province. Furthermore, the combined analyses revealed that the dust episode investigated was primarily associated with long-range atmospheric transport from Central Asian source regions, particularly Turkmenistan, Uzbekistan, and Kazakhstan. Backward trajectory simulations at different temporal scales showed that regional and local atmospheric circulation also contributed to the final distribution and accumulation of dust over the study area. Meanwhile, satellite-derived Aerosol Layer Height and Absorbing Aerosol Index products confirmed the presence of elevated aerosol concentrations over northeastern Iran and the eastern Caspian region before and during the event. These observations were consistent with HYSPLIT simulations and were further supported by increased PM₁₀ concentrations and reduced horizontal visibility recorded at synoptic stations, confirming the occurrence of a severe transboundary dust episode. Overall, the results highlight the Central Asian deserts as dominant external dust sources influencing northern Iran and reiterate the importance of atmospheric circulation patterns in controlling dust transport. Hence, the integrated methodology adopted in this study provides a reliable framework for identifying dust source regions and validating transport mechanisms through multiple independent datasets. Clearly, the findings contribute to a better understanding of transboundary dust dynamics in northeastern Iran that can be exploited toward developing early warning systems, air quality management strategies, and regional environmental policies. Future studies are recommended to investigate long-term dust variability using multi-year datasets, higher-resolution atmospheric models, and additional satellite products to improve the prediction and mitigation of dust-related environmental hazards.