الگوها و منابع داخلي ريزگردهاي تهران

The patterns and internal sources of dust in Tehran

اين پژوهش با هدف شناسايي الگوهاي اصلي ورود ريزگرد به تهران و تعيين منشاء­هاي داخلي تغذيه ريزگرده اي وارد شده تهران است. داده ­هاي مورد استفاده شامل داده ­هاي هواشناسي بازه 97-1384، داده ­هاي مربوط كيفيت هواي تهران در همان بازه زماني، تصاوير مربوط به سنجنده TM لندست 5 و OLI لندست 8 طي سال­هاي 1985 الي 2017، داده ­هاي سطح يك MODIS در تمامي ايام وقوع ريزگرد، نتايج آزمايش XRF مربوط به تله ­هاي رسوبگير نصب شده در مناطق تهران به عنوان مقصد و برداشت نمونه از مناطق مبدا بوده است. روش انجام پژوهش مدل جرياني HYSPLIT به روش پسگرد، براي رديابي ذرات در ارتفاع 500، 1000 و 1500 متري از سطح زمين و در حدفاصل زماني 3 روز قبل از وقوع طوفان گرد و غباري بوده است. همچنين از تصاوير سطح اول MODIS با شاخص BTD به آشكارسازي اين پديده در تمامي روزهاي وقوع ريزگرد پرداخته شده است. نمونه­ گيري از منطقه مقصد كه شهر تهران است و مناطق مبدا در مسير جريان ريزگردها شامل معادن شن و ماسه تهران شهريار (تراس­هاي آبرفتي رودخانه كرج)، تالاب ­هاي قنبر آباد و بند عليخان، پلاياهاي حوض سلطان و ميقان و مناطقي از دشت قزوين بوده است. يافته­ هاي حاصله از الگوهاي اصلي ورود ريزگرد به تهران، 5 الگوي اصلي را نشان داد كه عمدتا از خارج از كشور و در فصول مختلف وارد ايران مي ­شوند و هنگام عبور از برخي سطوح پست از قبيل درياچه­ ها و پلايا­ها و برخي چاله­ هاي داخلي مجددا تغذيه مي­ شوند.

Introduction Dust is one of the serious environmental problems of Iranian cities, including Tehran. In recent years, in the Iranian capital city of Tehran, which is close to nearby dry and wastelands, continuous droughts, rainfall, and temperature increases have intensified dust. The aim of this research is to identify the main patterns of dust entering Tehran and to determine the internal sources feeding the imported dust in Tehran. Materials and methods Materials used in this research include data from the synoptic stations of the meteorological organization of Iran during 2005-2017, data of Tehran Air Quality Control Company about days of dust occurrences, as well as TM Landsat 5 and OLI Landsat 8 imagery data from 1985 to 2017 (USGS), MODIS level1 Data for all days of the incident, results of the XRF test related to Marble dust collectors installed in Tehran’s regions as destination and finally sampling from areas of the source. To determine the route of dust particles HYSPLIT model of the U.S. National Oceanic and Atmospheric Administration website (NOAA) was used to estimate changes in vegetation in the surrounding areas using the Google earth Engineering System (GEE). First, all dust indices that reduce horizontal visibility to less than 1500 meters and are registered in neighboring stations and have non-local origins are counted from 2005 to 2017. Afterwards the BTA method of HYSPILIT model is used to track the air mass entrance to the Tehran Metropolitan during the days before the occurrence. Then the level 1 MODIS images were exposed using the BTD index during all days of the occurrence. It was demonstrated that the passage of flows moves through some forms and basins. The entrance on the way to Tehran is aggravating and increasing effects. These limits include: (sand mines close to Tehran, deserts around Qazvin, Hoze-Sultan and Meghan playa and Ghanbarabad-Alikhan wetlands. in order to examine the effects of these areas, dust sediment was sampled through XRF testing from both locations in Tehran, with the installation of modified MDCO dust marble collector and at dust exit areas, using a sampling of the surface layer. The results confirm the similarities between elements of Tehran samples and exterior origins. In order to examine the changes in the surface form of selected areas using NDVI Index and the supervised classification method using TM and OLI Landsat 5 and 8, the changes in these environments during the years 1985 to 2015 examine and then the role of these changes were evaluated on the intensification and strengthening of dust cores. Results and discussion The findings of the main patterns of the arrival of Tehran showed 5 main patterns that are mainly entering Iran from abroad. Patterns that come to Tehran during the warm season are mainly originated from northeast Syria and Iraq. These streams through the low altitude areas of Zagros and increase their sediment on the way at dry areas and plains around Qazvin and sand mines. Late winter and early spring streams from Saudi Arabia's deserts enter the central plateau of Iran and are fed by landforms such as Meghan pits and salty lands around Hoze-Sultan, Ghanbarabad Lake, and Alikhan Dam wetland. The streams that are mostly western-eastern and are compatible with western wind, move to Iraq and Iran after formation in East Africa and in Saudi Arabia. Also, once they cross some mean surfaces such as lakes and playa and internal dry holes, they are fed again. The results of the research show the role of landforms in the end-basins, including dried surface and sedimentary lakes, in the pattern of dust towards Tehran. Conclusion The main patterns of entering Tehran in different seasons, are mainly from abroad. The results show the role of end basins landforms, including dried lakes and sedimentary surfaces, in the pattern of dust to Tehran. The results of the sampling and laboratory analysis show the existence of similarities between chemical compounds of the elements sampled from the mine's surface and those sampled from the Tehran dust collectors.