Year

2020

Degree Name

Doctor of Philosophy

Department

School of Earth, Atmospheric and Life Sciences

Abstract

In the previous three decades, environmental and climatic systems have experienced considerable changes. These changes have probably influenced dust events in different areas in the world. Iraq represents one of the exposed regions to dust events. The study aims to (i) describe the spatialtemporal patterns of aerosol index values and dust events variability over Iraq using remote sensing data (AI-TOMS and OMI data with climate factors) and dust observations (suspended dust, rising dust and dust storms), (ii) identify the potential sources and transport pathways of dust storms over Iraq using ground and satellite data, (iii) identify signatures of the physical, mineralogical and chemical characteristics of chosen dust storms using grain size, XRD and XRF analyses and identify their possible sources using backward trajectories from the HYSPLIT model.

In order to obtain spatial and temporal distributions of dust events, aerosol index (AI) values from remote sensing satellites (TOMS - OMI) and dust events over Iraq (based on surface meteorological station observations of suspended dust, rising dust and dust storms) were analysed for different areas of Iraq over the study period 1980–2015. The results showed that AI values and dust events increased in spring-summer but a decreased in autumn-winter. The results showed a significant gradation of increasing AI values and dust activity from north to south, with the maximum AI and dust activity distributions above the southern and central regions of Iraq. The highest values of AI distribution from the TOMS were 2.06, 1.93, and 1.87 and for the OMI were 2.32, 2.27 and 2.24 in June above the northern, central and south regions, respectively, with lower values in December. The weather parameters (such as temperature, precipitation and winds) have a significant impact on defining the aerosol distribution variability above any region. Therefore, the spatial-temporal variability of AI values in conjunction with meteorological data (air temperature, wind speed, relative humidity and precipitation) in Iraq between 1980 and 2015 were examined. The results showed that there is an inverse correlation between AI and precipitation and relative humidity while there is a positive relationship between AI and both air temperatures and wind speeds. The cities near-desert areas (e.g. Baghdad, Basra and Nasiriya) suffer from the greatest frequency of dust storms compared to the northern and eastern regions. According to the annual average during the 35 years covered by the study, the frequency of major dust storm activity in Baghdad was 3.1 days, Basra 2.3 days and Nasiriya was 7.8 days. Suspended dust is more frequent in Iraq compared with rising dust or dust storms. Therefore, ground surface observations for dust events from meteorological stations can be used to monitor and analyse the spatiotemporal variability of dust types that cannot be determined by using satellite measurements. In order to determine the possible local, adjacent and distant dust sources and transport pathways of dust storms over Iraq, backward trajectories of air parcels data from the HYSPLIT model and wind roses (based on surface meteorological station observations of wind speeds and directions) were analysed for different areas of Iraq over the study period. According to the location and the dominant direction in wind roses and backward trajectories on dust storm days, the results showed that the potential local dust sources for study sites in Iraq were Al-Jazeera, Western and Southern Deserts and alluvial plain areas between the Euphrates and the Tigris Rivers. The southern, western and central areas of Iraq are located in a dry area that is characterized by low annual rainfall and water scarcity, therefore, they were considered to be major source areas for local dust storms in the region. The possible adjacent dust sources were the Syrian Desert, dry regions in Jordan, northern Kuwait, southwestern Iran, southern Turkey, and the An-Nafud and Ad Dahna Deserts in Saudi Arabia, while the likely remote dust sources were North African deserts. The prevailing transport paths of dust storms over Iraq mainly is northerly and northwesterly winds (Shamal), while southwest and southeast winds represent the second most familiar direction causing dust storms in Iraq. Thus, the wind directions and speed data analysis supplied some proof to indicate potential surrounding and local source areas for dust. Dust emissions from Syria and Iraq are caused by the dominant strong northwesterly wind. In order to provide a good understanding and information about dust activity, it is better to use both remote sensing satellite measurements and ground weather observations to determine the pathways of air masses and the potential local, neighbouring and remote sources and transport paths of dust storms over any study region in the world.

In order to assess the physical, mineralogical and chemical characteristics of dust storms, airborne dust samples were analysed for grain size, mineralogy and chemical composition to identify their possible dust sources, and the HYSPLIT model backward trajectories were determined for each dust storm in the different areas of Iraq. The results of particle size analysis showed that clay and silt particulates form an average of 86.9% of a dust storm, whereas sand particles represent an average of 13.2% of all dust samples. The physical analysis of dust samples revealed that low percentages of sand occur in the north region, but they are high in the western and central regions. The results of XRD analysis suggest that kaolinite, gypsum, albite, quartz, and calcite were the major mineral dust components. However, lower amounts of palygorskite, microcline, dolomite, illite, chlorite and halite were detected in some station samples. The XRF analysis suggested that Ba, Sr and Cl were the main trace element components in the airborne dust samples. In addition, the chemical analysis of dust samples revealed that high percentages of Zn and Pb occur in the eastern and central regions. The results of HYSPLIT backward trajectories analysis of air parcels revealed that the potential sources of dust storms were the Syrian Desert, North Africa Desert, An-Nafud Desert in Saudi Arabia, the dry lands in southwestern Turkey and southwest Iran, and the alluvial plain, Al Jazeera and Western Deserts in Iraq.

This thesis is unavailable until Wednesday, February 22, 2023

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.