تبیین تغییرات مکانی ریزگردهای تهران با رویکرد کیاس در معرفتشناسی فضایی (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
ریزگردهای ورودی به کلانشهر تهران از الگوی خاصی پیروی می کند که در پژوهش حاضر علل آن در دوره زمانی 2005 تا 2017 بررسی می شود. داده های استفاده شده در این پژوهش شامل روزهای وقوع ریزگردها و داده های ایستگاه های سینوبتیک تهران بوده است. در این مطالعه از مدل رهگیری بسته های هوا (HYSPLIT)، شاخص های آشکار سازی ریزگردها و تعیین خصوصیات شیمیایی گرد و غبار (از جمله عناصر اصلی و کمیاب از پهنه های انتخابی از روش فولوئورسنس اشعه ایکس XRF) استفاده شده است. یافته ها نشان داد که منشأ اولیه ریزگردهای ورودی به تهران در منطقه های بیابانی و خشک کشور های غرب و جنوب غربی ایران قرار دارد. بخش اعظم منابع خارجی ریزگرد مانند صحاری شمال عربستان و صحاری شرق آفریقا پدیده های جدیدی نیست و به رخداد ریزگردها در دوران جدید مربوط نمی شود، بلکه از گذشته فعّال بوده است و هیچ گاه از منطقه های داخلی ایران، شبیه تهران عبور نمی کردند که علت آن را باید در خشک شدن تالاب ها و دریاچه های داخلی جست وجو کرد. به طور کلی، تغییرات فراوانی مسیر ریزگرد ها و ارتباط آنها را با منابع ورودی نمی توان تبیین کرد؛ اما بیشتر به نظر می رسد که سیستم حرکتی ریزگردها در صدد برقراری نظمی عمیق تر است؛ زیرا ورودی مواد به سیستم دینامیکی ریزگردها در طول حرکت تغییر کرده است؛ در حالی که در مبدأ و شروع سیستم ریزگردها تغییرات چشمگیری رخ نداده است.Analyzing Spatial Dust Changes in Tehran Using Chaos Theory in Spatial Epistemology
This research investigated the specific patterns of dust influx into the metropolis of Tehran from 2005 to 2017. The study utilized the data on dust occurrence days and synoptic station data in Tehran. The research methodology involved employing the HYSPLIT trajectory model, as well as dust detection indices, and determining the chemical properties of dust, including main and rare elements, by using the X-Ray Fluorescence (XRF) method. The findings indicated that the primary source of dust entering Tehran originated from desert regions and vast, arid areas outside the country. External sources of dust, such as the North Arabian Sahara and the East African Sahara, have been active since ancient times and are not solely related to modern dust occurrences. The cause of their impact on Tehran could be attributed to the desiccation of internal lagoons and lakes. The changes in the frequency of fine-dust trajectories could not be solely explained by their connection with external sources. Instead, it appeared that the micro-particle movement system was striving to establish a deeper order, which was not solely influenced by changes in the origin and destination of the particles. Rather, the entry of fine particles into this movement system had undergone changes during their movement within the system.Keywords: Dust, Tehran, Chaos, HYSPLIT IntroductionThe shifting distribution of dust in various regions around the world has led to the presence of dust in major cities during certain seasons. Tehran has been particularly affected by this phenomenon from its onset. Despite the fact that numerous research efforts have aimed at understanding the origins of this phenomenon, the spatial patterns of its changes remain a topic of ongoing investigation. This study sought to elucidate the spatial dynamics of dust influx into Tehran by using a spatial epistemology approach. Analysis of MODIS images and their correlation with climate models was conducted for the period spanning 2005 to 2020. Preliminary findings indicated that the dust phenomenon adhered to specific patterns and pathways, from its initial emergence at focal points to its eventual arrival in the city of Tehran. Materials & MethodsTehran, the capital and one of the largest cities in the world, is situated on the southern slope of the Alborz highlands near the major permanent water networks of the region, namely the rivers of Karaj to the west and Jajrud to the east. The city grapples with various environmental challenges, including the issue of fine dust. Investigation into the trajectory of fine dust movement has revealed that the presence of features, such as playas, lakes, dried-up wetlands, old alluvial terraces, and sand mines significantly influences the arrival of fine dust in the area of Tehran. These particles are exceedingly small.Given the frequent occurrences of dust particles between 2000 and 2015 and availability of local data archives, the period from 2005 to 2017 was chosen for this study. Data collection was conducted in Tehran and its synoptic stations. Analysis of long-term wind-rose data from the indicator stations revealed that the prevailing wind direction in Tehran Province was predominantly from the west and south in most months. To identify regional dust sources, wind speed and direction maps were utilized and the HYSPLIT trajectory model was employed to track their paths. The HYSPLIT model in conjunction with atmospheric maps and satellite images was used to enhance the validity of the research findings for all dust events.Detection indices for fine dust, including the Brightness Temperature Difference (BTD) index, dust index method, and Miller's method, were utilized. Additionally, the X-Ray Fluorescence (XRF) method was employed to determine the chemical compositions of dust, including major and rare elements, in the samples collected from specific areas. The results obtained from climate modeling and MODIS image processing facilitated the identification of key areas influencing the movement patterns of fine dust toward Tehran. These areas predominantly corresponded to end basins (playas, lakes, lagoons) of old alluvial terraces and desert plains. Research FindingsThrough the analysis of MODIS images and their correlation with climate models spanning the years 2005 to 2020, it was established that the phenomenon of dust followed specific patterns and pathways from its origin at focal points to its arrival in Tehran. This pattern predominantly occurred in July with its initial flow originating from the northeast of Syria. Another pattern occurring in late winter and early spring originated from the Arabian Desert. Patterns with a more west-east axis corresponding to westerly currents originating from the deserts of northern Arabia predominantly occurred in the warm months of the year. Additionally, dust concentration nuclei might have been formed in East Africa and over Saudi Arabia, subsequently moving to Iraq and Iran. The primary source of dust entering Tehran was located in desert and arid expanses outside the country.Many of the external sources of dust, such as the North Arabian Sahara and the East African Sahara, are not new phenomena and have been active since ancient times, never previously extending into Iran's interior regions like Tehran. The current spread of this dynamic phenomenon is being investigated with its cause being attributed to drying of wetlands and internal lakes. The areas under scrutiny in this study included sand exploitation levels and sand mines in Tehran, Alikhan Dam, Hoze Soltan Lake, Mighan, and the desert lands around Qazvin Plain.Geochemical tests confirmed the similarity in elemental composition between the area and the dust collected in Tehran. The resemblance in chemical compositions of the elements sampled from mine surfaces and those collected with the MDCO sediment trap suggested that a significant portion of silicon dioxide (SiO2) found in the chemical compositions of dust in Tehran was likely sourced from the sand and sand mines of Tehran. This was because all dust-carrying streams passed over these mines, indicating the potential role of these mines in the elemental composition and deposition of dust in Tehran. MODIS images indicated the formation of dust condensation cores on the surfaces of Hoze Soltan and Mighan lakes, which had the potential to intensify dust flows. A comparison of the average compositions of Hoze Soltan, Mighan, and Tehran lakes revealed the presence of potassium and sodium compounds, as well as chlorine, similar to the samples from these lakes, suggesting that some of the elements of sodium, chlorine, and potassium entering Tehran might have been collected while passing through the fine-grained and separated lands around these lakes. Furthermore, the observations related to the geochemical sediment compositions of samples collected in Tehran using sediment traps compared to those collected in Qazvin Plain showed the significant presence of chlorine, potassium, and silicon among the elements. Discussion of Results & ConclusionThe research findings revealed that the sources influencing the alterations in the trajectory of micro-storms demonstrated spatial adaptation to playas, wetlands, and end basins in general. In essence, there were discernible changes in the frequency of dust entry patterns in Tehran and these changes could not be solely attributed to their connection with the input sources. Instead, it appeared that the micro-particle movement system was striving to establish a more deeply organized structure independent of changes in its origin and destination. Rather, the entry of fine particles into this movement system had undergone modifications during their transit within the system. Consequently, alterations were being introduced to the initial conditions within the system governing dust entry into Tehran from its feeding sources. Although the dimensions of these sources were relatively small compared to the original source, they could significantly impact the trajectory of fine particles. Laboratory studies on the samples from Tehran's sediment traps, as well as sand mines, Alikhan Dam, Hoze Soltan and Mighan lakes, and the desert lands around Qazvin Plain, underscored their role in contributing to fine dust in Tehran.
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