Aeolian dust deposition rates in south-western Iran
The annual atmospheric dust-load originating in the so-called Dust Belt , which ranges from the Sahara desert and the Arabian peninsula to the arid lowlands of Central Asia and the deserts of northern China, impacts the air quality and the climate worldwide. Iran as a whole, and especially the s...
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| Format: | Dissertation |
| Sprache: | Englisch |
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Philipps-Universität Marburg
2020
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| Zusammenfassung: | The annual atmospheric dust-load originating in the so-called Dust Belt , which ranges from the Sahara desert and the Arabian peninsula to the arid lowlands of Central Asia and the deserts of northern China, impacts the air quality and the climate worldwide. Iran as a whole, and especially the southwestern regions of the country, most affected by dust, with frequent dust storms characterized by annual mean concentrations of more than 100 µg/m³ of suspended dust. Although aeolian dust is a highly relevant problem in Iran, there is a lack of comprehensive regional studies on this topic. The central aim of the study presented here is therefore the spatiotemporal analyses and classification of dust events, the chemical composition of the dust, and the connections between regional and seasonal climate variation and dust deposition rates in four sub-regions of Iran. This comprehensive approach is based on the maximum mean dust concentration and the seasonality of dust events. The results are provided new and valuable insights into the dust deposition and its related processes in the study area.
The study area covers 8.43% of Iran (about 117,000 km2), located between 45°30′00″ E 35°00′00″ N and 49°30′00″ E 30°00′00″ N including Kermanshah, Lorestan and Khuzestan. The fieldwork area is characterized by the rolling mountainous terrain about 4000 m above sea level (a.s.l) in the north and east, plains and marshlands in the south. Study area has also located in dry climate and hot summer conditions in the south, cold and hot desert climates in the west. The studies on aeolian dust in southwestern Iran are based solely on ground deposition rates from 2014 to 2017.
To address the connections between the Ground observation of dust Deposition Rates (GDR), climate zones, and weather patterns, a comparative analysis with various data sets was conducted. Both gravimetric and directional dust samplers (10 each) were installed to record the monthly GDR between 2014 and 2017. The sampler design was deliberately kept simple to ensure long-term durability and easy maintenance. The collected dust samples were analyzed for their chemical composition using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The ten sampling sites were also classified by their land use / land cover (LULC) for a more detailed data interpretation. The observation data during two typical dust cases (spring 2014 and winter 2015), have furthermore been compared with the spatiotemporal dust concentration and dust load over the study area. Comparing the results of the monthly mean Aerosol Optical Thickness (AOT) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and GDR data, using enhancement algorithms were applied in order to investigate the spatiotemporal distribution of dust events. To demonstrate the aerosol movement, a HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used for tracing the investigated dust events. The time-space consistency between AOT and GDR, in agreement with the HYSPLIT model output was the basis for an improved estimation of the dust deposition rate from separate thickness layers. Finally, by comparing the high temporal and maximum seasonal deposition rates, using MODIS and GDR data, the impact of the regional climate on the deposition rates of aeolian dust was assessed, which allows insights in potential future dust emission scenarios in times of climate change.
A major finding shows the impact of dust events on the environment and considers the influence of geographical factors, such as weathering, and climate pattern over aeolian dust deposition rates. In more detail, finding to address the first objective suggested that contributors of the elemental concentrations are associated with elements emanating from local industrial and commercial activities (Cr, V, and Cd). The dominant variables (K, Zn) strongly influence the aerosol composition values and represent the dust transport route. Inter –element relationships shows that the highest proportion (80%) of dust samples subjected to Airborne Metals Regulations are formed under local and regional conditions. Besides, the analyses indicate that the WRF-Chem model adequately simulates the evolution, spatial distribution and load of dust over the study area. Hence, the model performance has been evaluated by GDR. It showed different values of GDR highly depending on LULC pattern. Due to the fact, that there is no way to isolate each individual area from the effects of either anthropogenic sources or natural weathering processes, developing guidance on the priorities of expanding projects and preventative actions towards potential dust deposition from natural and dominant sources may be a subject of institutional interest.
The results of direct measurements of dust deposition, which are typically made by passive sampling techniques (ground-based observations), along with analyzed data from AOT, represent the second objective to understand the spatiotemporal pattern of the points with the same variation. The corresponding points headed to find moving air mass trajectories, using HYSPLIT were proven to be a discriminator of their local and regional origin of aeolian dust. Furthermore, the seasonal deposition rate varied from 8.4 g/m2/month in the summer to 3.5 g/m2/month in the spring. Despite all the advances of AOT, under certain circumstances, the ground-based solutions were able to represent aerosol conditions over the research area, tested in the southwestern regions of Iran. And that is when the low number of observations is a commonly acknowledged drawback of GDR.
In addition, the peak of the seasonal deposition rates (t/km2/month) occurred in [arid desert hot-BWh, 8.4], [arid steppe hot-BSh, 6.6], and [hot and dry summer-Csa, 3.5] climate regions. Thus, the third objective response was detected as the highest deposition rates of dust BWh >BSh >Csa throughout the year, once the annual mean deposition rates (t/km2/year) are 100.80 for [BWh], 79.27 for [BSh], and 39.60 for [Csa]. The knowledge gained on the dust deposition processes, together with the feedback from the climate pattern, will provide insights into the records of data for developing new sources, deposition rates and their climate offsets. Taking this in mind, having information about the ground deposition rates in the study region could make the estimations more accurate, while finding an appropriate algorithm is necessary to enhance the affected areas exposed to the dust. In order to assess the impact of dust events on human health, environment and the damage to the various business sectors of the country’s economy, additional studies with adequate modelling tools are needed.
Due to this date, the data holding organizations are somewhat reluctant to make their data available to other parties. This work is also a step toward an institutional suggestion to gain benefit from information exchange amongst data holding organizations, providers and users. The need for capacity building and strong policy for implementing user-friendly geo information portal is essential. |
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| Umfang: | 159 Seiten |
| DOI: | 10.17192/z2020.0500 |