Assessment of geochemical and sedimentological characteristics of atmospheric dust in Shiraz,southwest Iran

Geogenic dust is commonly believed to be one of the most important environmental problems in the Middle East.The present study investigated the geochemical characteristics of atmospheric dust particles in Shiraz City(south of Iran).Atmospheric dust samples were collected through a dry collector method by using glass trays at 10 location sites in May 2018.Elemental composition was analysed through inductively coupled plasma optical emission spectrometry.Meteorological data showed that the dustiest days were usually in spring and summer,particularly in April.X-ray diffraction analysis of atmospheric dust samples indicated that the mineralogical composition of atmospheric dust was calcite+dolomite(24%)palygorskite(18%)quartz(14%)muscovite(13%)albite(11%)kaolinite(7%)gypsum(7%)zircon=anatase(3%).The high occurrence of palygorskite(16%-23%) could serve as a tracer of the source areas of dust storms from the desert of Iraq and Saudi Arabia to the South of Iran.Scanning electron microscopy indicated that the sizes of the collected dust varied from 50 μm to0.8 μm,but 10 μm was the predominant size.The atmospheric dust collected had prismatic trigonal-rhombohedral crystals and semi-rounded irregular shapes.Moreover,diatoms were detected in several samples,suggesting that emissions from dry-bed lakes,such as Hoor Al-Azim Wetland(located in the southwest of Iran),also contributed to the dust load.Backward trajectory simulations were performed at the date of sampling by using the NOAA HYSPLIT model.Results showed that the sources of atmospheric dust in the study area were the eastern area of Iraq,eastern desert of Saudi Arabia,Kuwait and Khuzestan Province.The Ca/Al ratio of the collected samples(1.14) was different from the upper continental crust(UCC) value(UCC=0.37),whereas Mg/A1(0.29),K/Al(0.22) and Ti/Al(0.07) ratios were close to the UCC value(0.04).This condition favours desert calcisols as the main mineral dust sources.Analysis of the crustal enrichment factor(EF_(crustal)) revealed geogenic sources for V,Mo,Pb,Sr,Cu and Zn(2),whereas anthropogenic sources affected As,Cd,Cr and Ni.     

Analysis of an oasis microclimate in China’s hyperarid zone

The microclimate of a desert oasis in China’s hyperarid zone was monitored, analysed and compared to that of nearby forested lands. Factors associated with differences in photosynthetically active radiation (PAR) between clear, cloudy and dust storm days are discussed. Desert oases were shown to fulfill ecological functions such as altering solar radiation, adjusting near-ground and land surface temperatures, reducing temperature differences, lowering wind velocity, and increasing soil and atmospheric humidity. Total solar radiation within the oasis was roughly half that above the forest canopy. During the growing season, air temperatures in Populus euphratica Olivier and Tamarix ramosissima Ledeb. woodlands were, on average, 1.62 and 0.83°C lower, respectively, than that in surrounding woodlands. The greater the forest cover, the greater was the difference in temperature. Air temperature was higher at the upper storey than that at the lower storey of the community, i.e., air temperature increased with increasing height above the soil surface. During the growing season, relative humidity was higher in woodlands than in surrounding areas: relative humidity in P. euphratica and T. ramosissima woodlands were, on average, 8.5 and 4.2% higher, respectively, than that in the surrounding area. Mean wind velocity in the P. euphratica forest land was 0.33 m/s, 2.31 m/s lower than that in the surrounding area. On dust storm days PAR and total radiation, Q, were significantly lower than that on cloudy or clear days. Their ratio, η _Q  = PAR/Q, was larger and much more variable on dust storm days than that on clear or cloudy days.     

Spatiotemporal analysis of dust patterns over Mesopotamia and their impact on Khuzestan province,Iran

Dust storms are yet quite frequent in various parts of the world, particularly ancient Mesopotamia (approximately corresponding to most parts of Iraq as well as certain surrounding regions toward its north). To add to the ongoing difficulty, monitoring dust patterns has been proven to be a rather difficult endeavor given the absence of reliable ground-based monitoring stations in the corresponding area. Additionally, western provinces of Iran, especially Khuzestan in the southwest of Iran, have been severely affected by dust storms carried by the westerly winds, blown through neighboring countries in ancient Mesopotamia. This study proceeds to employ aerosol optical depth (AOD), extracted from the MODerate-resolution Imaging Spectroradiometer onboard the Terra spacecraft, to assess spatial dust variations between 2001 and 2017 over the Khuzestan province and ancient Mesopotamia. The variations were also correlated with the temporal dust changes in the Khuzestan province. Frequency of occurrence for AOD?>?1 was used to identify and categorize major dust sources in the aforementioned regions. The findings were indicative of an increasing trend in the annual AODs of the Khuzestan province, which eventually led to a significant increase from 2008 toward the end of 2012, but decreased again in the following years. Correspondingly, the entire time period (2001–2017) was further divided into three sub-periods: the first time period spanning from 2001 to 2007, followed by the second from 2008 to 2012 and finally a third time period from 2013 to 2017. Dust source identification was speculative of numerous dust spots in Iraq, Syria, Kuwait and also the southern parts of Khuzestan province which have become more active in recent years. Additionally, a large active dust spot was pinpointed between the northwest Iraq and eastern Syria border which has become extremely active during the second time period, possibly due to a severe drought in the Fertile Crescent.

     

Sensitivity of meteorological input and soil properties in simulating aerosols (dust,PM10, and BC) using CHIMERE chemistry transport model

The objective of this study is to evaluate the ability of a European chemistry transport model, ‘CHIMERE’ driven by the US meteorological model MM5, in simulating aerosol concentrations [dust, PM₁₀ and black carbon (BC)] over the Indian region. An evaluation of a meteorological event (dust storm); impact of change in soil related parameters and meteorological input grid resolution on these aerosol concentrations has been performed. Dust storm simulation over Indo-Gangetic basin indicates ability of the model to capture dust storm events. Measured (AERONET data) and simulated parameters such as aerosol optical depth (AOD) and Angstrom exponent are used to evaluate the performance of the model to capture the dust storm event. A sensitivity study is performed to investigate the impact of change in soil characteristics (thickness of the soil layer in contact with air, volumetric water, and air content of the soil) and meteorological input grid resolution on the aerosol (dust, PM₁₀, BC) distribution. Results show that soil parameters and meteorological input grid resolution have an important impact on spatial distribution of aerosol (dust, PM₁₀, BC) concentrations.     

Magnetic properties of airborne particulate matter in Shanghai during dust storm events and the implications for heavy metal contaminant sources

Airborne particulate samples (including dust storm period samples) were collected from the Putuo, Qingpu and Minhang districts of Shanghai city from October, 2009 to October, 2010, and also tracked the dust transporting pathways from NW (Northwest) to SE (Southeast) including the cities of Xi’an, Beijing, Zhengzhou and Nantong, as a means of sampling the dust storm particulate matter in the spring of 2010. After measuring the magnetic parameters and the concentrations of particles and heavy metals, their magnetic properties were analyzed to track the source locations of heavy metal pollution during dust storm events, and then combined for backward trajectory analysis. It was found that the slightly polluted dust particles carried many contaminants during dust storm periods when the dust palls were transported by winter monsoon winds from the NW desert region towards the SE. The contaminants were further increased by contributions of fine SP&SD grains derived from local automobile exhausts in Shanghai as well as being enriched also in Northern cities during non-dust storm periods. A significantly positive linear relation was found between the χ_lf and SIRM of loess and the storm dust, indicating a similar material source for these two kinds of samples. A higher χ_lf and SIRM in storm dust content compared to loess suggests that storm dust contains not only materials from natural sources, but also those from partly anthropogenic sources. Backward trajectory analysis indicates intuitively the source region of the Shanghai storm dust. These conclusions have important scientific significance for research on long-distance transportation of contaminants (such as heavy metals) adsorbed onto airborne particulate matter during dust storm events.     

Dust emission and transport in Mali, West Africa

Vertical dust fluxes were measured in the Inland Delta region of the Niger River, Mali, West Africa, during April-June, 1989 and 1990. Measurements of dust flux represent, for the most part, non-dust storm conditions or ‘dust haze’ periods. The observed concentration versus height relationships are similar to data presented by other investigators. The relationship between wind shear velocity (u_*, m s^?1) and vertical dust flux (F, μg m^?2 s^?1) can be described by a relationship in which F is proportional to u_*⁴. However, there is considerable scatter within the data set which is attributable to textural controls and surface conditions. The vertical dust fluxes measured in Mali are compared to dust fluxes measured in Texas, USA, and Yukon Territories, Canada. The significantly different values for the constant of proportionality (a) in the F α a u_*⁴ relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream. Dust concentrations measured in Mali were found to be uniformly high and in general exceed WHO health standards for acceptable total suspended particulate loadings. As a result background dust may be considered a long term stress on health for the people of this region of Mali.     

Mapping and monitoring of dust storms in Iran by fuzzy clustering and remote sensing techniques

In this research, the frequency of dust storms was prepared at 87 synoptic stations for the period of 1987–2013. These data were classified by means of Fuzzy c-means clustering algorithm. Satellite images of MODIS and brightness temperature index were also used for detection and tracking dust storm of 30 Jun 4 July 2008. The results indicated that Iran is classified in five clusters by the dust-storm-frequencies from which, cluster 5 is reclassified in three clusters because of its wide range. The maximum number of days with dust storms was observed in cluster 1 that includes only Zabol station with the frequency of 790 days with the duration 1987–2013. The minimum number of days with dust storms was observed in cluster 5-3 that includes the stations located in portions of North, Northwest, Northeast Iran and the higher elevations of the Zagros in western Iran. A case study about a severe dust storm in Iran using satellite images indicate that brightness temperature index (BTI) is a desired index for detection and monitoring of dust storms. The source of the investigated dust storms is Iraq and South of the Arabian Peninsula that had influenced the western half of Iran in several days. The frequency of dust storms increased markedly in the west, southwest of Iran and Persian Gulf around as main receptors from emerging dusty areas but it increased slightly in the eastern half of Iran.     

Dust storms loads analyses—Iraq

The dust storms that blow over Iraq were studied from December 2008 to March 2009. The total number of studied dust storms was eight; during each dust storm, samples were collected from the cities of Baghdad, Ramadi, Kut, Basra, Najaf, Karbala, Hilla and Tikrit. The climatic elements with the dust storms types were studied. The results of dust storms analyses reflect their increase in average toward the southwestern direction (average suspended, rising, regional dust storms were 8, 10, 15 days/year, respectively). The average means annual rainfall (in mm), evaporation (in mm), temperature (in °C), and relative humidity percentage indicate that there were remarkable variations in values, with increase of the number of days/years of the dust storms reflecting the effect of the regional climatic change. The results of particle size analyses indicate the texture of most samples range from sandy clayey silt (75%) and clayey sandy silt (25%), and the average dominant grain size have a direct relationship with trajectories of dust storms. Quartz grains were 15% rounded and 85% sub-rounded. Moreover, the dust samples were analyzed and identified by using XRD analyses and Polaroid microscope. The results reflect the following minerals according to their average relative dominant, quartz 58.6%, feldspars 17.3%, and calcite 15.4%, with small amount of gypsum 5.5%. The clay minerals (chlorite, illite, montmorillonite, palygorskite, and kaolinite) were recognized. The analyses of heavy minerals percentages by using the microscope were performed. The results of pollen distribution, in descending order, were Chenopodiaceous, Graminea, Pine, Artemisia, Palmae, Olea, and Typha (reaching 79%, 69%, 63%, 53%, 17%, 9%, and 7% of the counted pollen grains, respectively). The results of microorganisms (i.e., isolated bacteria and fungi), in descending order, were the gram-positive Bacillus species (42.9%), Aspergillus species plus Candida albicans (13.8%), and (8.4%), the gram-negative rods, Escherichia coli (9.5%), the gram-positive Cocci streptococcus pneumonia (6.7%), then the gram-negative rod Enterobacter cloacae (4.3%), Staphylococcus epidermidis, and Staphylococcus (3.9%) and (1.9%). The remaining Gram-negative microorganisms were Pseudomonas aeruginosa (2.7%). Regarding the viral etiology, there is no viral isolate among the work results. The allergens commonly associated with dust storms include fungal spores, plant and grass pollens, and organic detritus represent agricultural area pollen grains.     

Strontium isotope composition and petrogenesis of the Kirkpatrick basalt,Queen Alexandra Range,Antarctica

The initial ⁸⁷Sr/⁸⁶Sr ratios of twelve basalt flows of Jurassic age on Storm Peak in the Queen Alexandra Range are anomalously high and range from 0.7094–0.7133. The average value is 0.7112±0.0013 (1). The concentrations of rubidium and strontium have arithmetic means of 60.6±19.4 ppm and 128.8±11.9 ppm, respectively. The corresponding average Rb/Sr ratio is 0.47 which is also anomalously high for rocks of basaltic composition. In addition, these rocks have high concentrations of SiO₂ (56.50%) and K₂O (1.29%) and are depleted in Al₂O₃ (12.92%), MgO (3.44%) and CaO (7.91%) compared to average continental tholeiites. They are nevertheless classified as basalts on the basis of the composition of microphenocrysts.The initial ⁸⁷Sr/⁸⁶Sr ratios and all of the chemical parameters of the flows exhibit systematic stratigraphic variations. These are interpreted as indicating the occurrence of four eruptive cycles. In a typical cycle the initial ⁸⁷Sr/⁸⁶Sr ratios of successive flows and their concentrations of SiO₂, FeO (total iron), Na₂O, K₂O, P₂O₅, Rb and Sr decrease in ascending stratigraphic sequence while the concentrations of TiO₂, Al₂O₃, MgO, CaO and MnO increase upward. The initial ⁸⁷Sr/⁸⁶Sr ratios of the flows show a strong positive correlation with the strontium concentration. Similar correlations are observed between the initial ⁸⁷Sr/⁸⁶Sr ratios and all of the major oxide components. These relationships are incompatible with the hypothesis that these flows are the products of crystal fractionation of a-34 magma at depth under closed-system conditions. It is suggested that the flows resulted from the hybridization of a normal tholeiite basalt magma by assimilation of varying amounts of granitic rocks in the Precambrian basement which underlies the entire Transantarctic Mountain chain.Mixtures of two components having different ⁸⁷Sr/⁸⁶Sr ratios and differing strontium concentrations are related to each other by hyperbolic mixing equation. Such an equation was fitted by least squares regression of data points to a straight line in coordinates of initial ⁸⁷Sr/⁸⁶Sr and the reciprocals of the concentrations of strontium. This equation and plots of strontium versus other oxides were then used to estimate the chemical composition of the parent basalt magma and of the granitic contaminant by substituting reasonable estimates of their ⁸⁷Sr/⁸⁶Sr ratios. The chemical composition of the parent basalt (⁸⁷Sr/⁸⁶Sr=0.706) is generally compatible with that of average continental tholeiite, but is distinctive by having a low concentration of strontium (117 ppm). The chemical composition of the contaminant (⁸⁷Sr/⁸⁶Sr=0.720) is enriched in strontium (173 ppm), SiO₂, FeO (total iron) and the alkalies but is depleted in Al₂O₃, MgO and CaO. The data for strontium indicate that the lava flows on Storm Peak contain between 20 and 40% of this granitic contaminant. The contamination of basalt magma is not a local event but is characteristic of the Jurassic basalt flows and diabase sills throughout the Transantarctic Mountains and in Tasmania.Laboratory for Isotope Geology and Geochemistry, Contribution No. 33.     

Speciation of heavy metals in airborne particles, road dusts, and soils along expressways in China

This study analyzed the concentrations and chemical forms of Zn,Cu,Pb,Sb,Cd and Mn in airborne particles,road dusts and soils collected along three expressways in Jiangxi Province,China,with different traffic densities,and identified the levels and sources of heavy metal contamination.The concentrations of Zn,Cu,Pb,Sb,and Cd except Mn in airborne particles,road dusts and soils were all in direct proportion to traffic volume.Cd concentrations were low compared with other metals.For instance,the concentrations of Zn,Cu,Pb,Sb,Mn and Cd were 6.6,0.7,2.2,0.1,0.1 and 0.1μg·m-3in PM10along the Changjiu Expressway,792.8,241.4,248.3,9.6,340.5and 8.0 mg·kg-1in road dusts,and 201.1,143.2,59.5,9.5,338.9 and 2.3 mg·kg-1in soils,respectively,but in the case of the ratio of concentration to the environmental background value,most serious contamination was caused by Cd.The sources of the heavy metals were judged by comparisons of the chemical forms of the heavy metals in different environmental media.Pb and Mn in airborne particles were both derived from traffic;Pb in road dusts and soils resulted mainly from the use of leaded gasoline in the past;and Mn in road dusts and soils was derived from parent rocks.Zn,Cu,Sb and Cd in airborne particles,road dusts and soils were derived primarily from traffic,and differences in chemical forms of the heavy metals in different media were due to the interaction between heavy metals in airborne particles and organic matter and other surfaces in road dusts and soils.We also discussed the change of chemical forms of heavy metals in particles of different sizes and under different weather conditions.Bioavailability of heavy metals in airborne particles was much higher than that in road dusts and soils,especially Pb(0.676 in airborne particles,0.159 in road dusts and 0.095 in soils).     

Sr isotopic and elemental characteristics of calcites in the Chinese deserts: Implications for eolian Sr transport and seawater Sr evolution

Calcite content, Sr concentrations, and isotopes of calcites in the Chinese deserts are systematically studied in this paper. Calcite contents, which are calculated according to acid-soluble Ca contents in the deserts, are generally higher in the sandy deserts than in the sandy lands and decrease roughly from northwest to northeast of China. Acid-soluble Sr is well correlated with calcite in the Chinese deserts, implying acid-soluble Sr comes mainly from the calcite dissolution. Sr concentrations in calcites, calculated on the basis of calcite contents and acid-soluble Sr concentrations in the deserts, have an inverse relation to calcite contents, essentially mirroring the degree of Sr substitution for Ca in the calcite development. Desert calcites have regional variations in Sr isotopic ratios. Calcite Sr isotopic ratios depend on geological settings and chemical weathering. The Badain Jaran, and Tengger deserts are probably affected by additional factors such as the remote groundwater cycle or overturning of underlying sand deposits.Only four deserts (Taklimakan, Qaidam, Badain Jaran, and Tengger) appear to be potential sources of eolian deposits in the Chinese Loess Plateau (CLP). Isotopic signatures of calcite Sr and silicate Nd further indicate that the Tengger desert was not an important source for eolian deposits in the CLP. Eolian calcite was probably enriched due to wind sorting from the potential sources to the CLP and suffered weathering–leaching after it accumulated in the CLP. Sr isotopic compositions and Ca/Sr molar ratios of calcites are different between the deserts and the Lingtai profile, due to the integrated effect of wind sorting and weathering–leaching.It is essential to calculate accurately the ⁸⁷Sr/⁸⁶Sr ratio and Sr concentration of eolian calcite entering the oceans according to geochemical data of the Chinese deserts, because of the importance of the Chinese deserts in the global dust cycle. The calculated Sr concentration and ⁸⁷Sr/⁸⁶Sr ratio of eolian calcite entering the North Pacific Ocean, are 11.75 μmol/g and 0.71032, respectively. The calculated values in this study are close to the recommended values by Jacobson [Jacobson A. D. (2004) Has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine ⁸⁷Sr/⁸⁶Sr ratios over the past 2.5 million years? Geochem. Geophys. Geosyst. 5(12), 1–9, Q12002. doi:10.1029/2004GC000750]. Using the same model as that of Jacobson (2004), the effect of Asia dust on the evolution of seawater Sr isotopes is evaluated. (⁸⁷Sr/⁸⁶Sr)_seawater increases by 0.3 × 10⁻⁵ if the lower dust flux of 2.34 × 10⁸ mol Sr/yr is used in the model, suggesting the little effect of Asian dust on the seawater Sr record in the Quaternary. The increase in (⁸⁷Sr/⁸⁶Sr)_seawater is 1.5 × 10⁻⁵ if the higher value of 1.17 × 10⁹ mol Sr/yr is used, as observed in the Quaternary Sr record. These results further support the suggestions of Jacobson (2004).     

贵州新民铝土矿矿床Li的地球化学特征与富集机制探究

新民铝土矿床位于黔北务川-正安-道真地区(简称务正道地区)大塘向斜东翼,铝土矿(岩)型Li资源丰富.含矿岩系大竹园组(P1d)不同岩性的w(Li)有差别:土状-半土状铝土矿平均w(Li)为16.34×10-6,致密块状铝土矿平均w(Li)是803.84×10-6,铝土岩平均w(Li)是1436.22×10-6,黏土岩的平均w(Li)是786.62×10-6,梁山组泥岩的平均w(Li)是51.82×10-,韩家店群泥岩(页岩)的平均w(Li)是48.52×10-6,黄龙组灰岩的平均w(Li)是 11.99×10-6.由此可知,研究区铝土矿(岩)型Li资源主要富集在含矿岩系中上部的致密块状铝土矿、铝土岩和黏土岩中,顶板、底板以及土状-半土状铝土矿w(Li)较低.Li主要赋存于高岭石中,伊利石(水云母)和残存的三水铝石、勃姆石也可富集少量Li,当样品中赋锂矿物(高岭石、伊利石(水云母)、三水铝石和勃姆石)都存在时,高w(Li),主量元素w(Al3O2)、w(SiO2)、w(MgO)、w(K2O)、w(TiO2)和w(TFe2O3)与w(Li)的相关性也证实了上述结果.研究区的地球化学比值 CIA、w(Sr)/w(Cu)、u(CaO)/w(MgO)、w(Sr)/w(Ba)、w(V)/w(V+Ni)和 w(La)/w(Y)综合显示,炎热潮湿的古气候下,有机质腐烂形成酸性环境,半封闭海湾环境下,黏土化阶段中等强烈的化学风化程度和适宜的风化暴露剥蚀时间利于铝硅酸盐矿物和硅酸盐矿物化学键断裂,富集Al3+形成高岭石;风化程度过于强烈和长时间的风化剥蚀,继续脱Si富Al形成以硬水铝石为主的铝土矿;弱酸性-弱碱性以及氧化-还原过渡条件下,使得高岭石能最大程度的吸附Li元素.     

The effects of Typhoon Morakot on concentration of airborne particulates derived from unvegetated riverbanks

Landslides frequently occur during large earthquakes and storms in Taiwan, supplying large volumes of sediment to downslope areas. When coupled with the intense northeast monsoon over Taiwan in the dry winter season, this can lead to high concentrations of airborne particulates that are hazardous to human health. Air quality monitoring stations near unvegetated riverbanks recorded high concentrations of particulate matter less than 10 μm (PM₁₀) after Typhoon Morakot in 2009. The objective of this study was, therefore, to analyze the effects on air quality of sediment caused by the typhoon. A deflation module was simulated, and the resulting estimates were compared with observed data from the Taitung monitoring station for 2004 and 2005. The relationship of dust flux to average atmospheric dust concentration was analyzed for October to December 2001–2010. Analysis showed that the 2001–2008 data are highly correlated (0.78) with the average concentration. The intercept of 28.07 represented the background concentration with no dust emission, from October to December of 2001–2008. Based on the dust flux potential in 2009, the average yearly PM₁₀ concentration would be 37.98 µg/m³; however, the measured concentration was 61.67 µg/m³ from October to December. This suggests the strong influence of dust re-suspended from unvegetated riverbanks by Typhoon Morakot.     

Chemical and Isotopic Characters of the Water and Suspended Particulate Materials in the Yellow River and Their Geological and Environmental Implications

The chemical and isotopic characteristics of the water and suspended particulate materials(SPM)in the Yellow River were investigated on the samples collected from 29 hydrological monitoring stations in the mainstem and several major tributaries during 2004 to 2007.TheδD andδ~(18)O values of the Yellow River water vary in large ranges from-32‰to-91‰and from-3.1‰to-12.5‰,respectively.The characters of H and O isotope variations indicate that the major sources of the Yellow River water are meteoric water and snow melting water,and water cycle in the Yellow River basin is affected strongly by evaporation process and human activity.The average SPM content(9.635g/L)of the Yellow River is the highest among the world large rivers.Compared with the Yangtze River,the Yellow River SPM has much lower clay content and significantly higher contents of clastic silicates and carbonates.In comparison to the upper crust rocks,the Yellow River SPM contains less SiO_2,CaO,K_2O and Na_2O,but more TFe_2O_3,Co,Ni,Cu,Zn,Pb and Cd.The abnormal high Cd contents found in some sample may be related to local industrial activity.The REE contents and distribution pattern of the Yellow River SPM are very close to the average value of the global shale.The averageδ~(30)Si_(SPM)in the Yellow River(-0.11‰)is slightly higher than the average value(-0.22‰)of the Yangtze River SPM.The major factors controlling theδ~(30)Si_(SPM)of the Yellow River are the soil supply,the isotopic composition of the soil and the climate conditions.The TDS in the Yellow River are the highest among those of world large rivers.Fair correlations are observed among Cl~-,Na~+,K~+,and Mg~(2+)contents of the Yellow River water,indicating the effect of evaporation.The Ca~(2+)and Sr~(2+)concentrations show good correlation to the SO_4~(2-)concentration rather than HCO_3~-concentration,reflecting its origin from evaporates.The NO_3~-contents are affected by farmland fertilization.The Cu,Zn and Cd contents in dissolved load of the Yellow River water are all higher than those of average world large rivers,reflecting the effect of human activity.The dissolved load in the Yellow River water generally shows a REE distribution pattern parallel to those for the Yangtze River and the Xijiang River.Theδ~(30)Si values of the dissolved silicon vary in a range from 0.4‰to 2.9‰,averaging1.34‰.The major processes controlling the D_(Si)andδ~(30)Si_(Diss)of the Yellow River water are the weathering process of silicate rocks,growth of phytolith in plants,evaporation,dissolution of phytolith in soil,growth of fresh water diatom,adsorption and desorption of aqueous monosilicic acid on iron oxide and human activities.The averageδ~(30)Si_(Diss)value of the Yellow River is significantly lower than that of the Nile River,Yangtze River and Siberia rivers,but higher than those of other rivers,reflecting their differences in chemical weathering and biological activity.Theδ~(34)S_(SO4)values of the Yellow River water range from-3.8‰to 14.1‰,averaging 7.97‰.There is some correlation between SO_4~(2-)content andδ~(34)S_(SO4).The factors controlling theδ~(34)S_(SO4)of the Yellow River water are the SO_4 in the meteoric water,the SO_4 from gypsum or anhydrite in evaporite rocks,oxidation and dissolution of sulfides in the mineral deposits,magmatic rocks and sedimentary rocks,the sulfate reduction and precipitation process and the sulfate from fertilizer.The~(87)Sr/~(86)Sr ratios of all samplesrange from 0.71041 to 0.71237,averaging 0.71128.The variations in the~(87)Sr/~(86)Sr ratio and Sr concentration of river water are primarily caused by mixing of waters of various origins with different~(87)Sr/~(86)Sr ratios and Sr contents resulting from water-rock interaction with different rock types.     

Spatial and temporal trends of dust storms across desert regions of Iran

Dust storms are among natural and anthropogenic hazards for socioeconomic resources, especially in desert regions. In recent years, dust storms have become a serious problem, especially in desert regions of Iran. This study investigates temporal and spatial variation of dust storm frequency in desert regions of Iran. The number of dusty days (NDD) are collected from 22 stations across the region. The statistical analysis of NDD time series is carried out to show both spatial and seasonal pattern of dust storm occurrence in the region. The regional map of statistical characteristics indicates a north to south increasing dust storm frequency. The spatial map also reveals higher year-to-year variation in south eastern Iran. The seasonality of NDD shows the highest frequency for summer followed by the spring and autumn seasons. The popular Mann–Kendall and the bootstrap MK test to consider serial correlation are then applied for Trend assessment. Results showed both negative (across the north and northwestern regions) and positive trend (across south and south eastern regions) in the annual and seasonal NDD time series. This north-to-south gradient in the spatial and temporal frequency NDD may arise from harsh dry and gusty winds as well as intense land use change in the south eastern territories of Iran. However, more careful and detailed studies are required to connect environmental conditions to change in NDD frequency.     

Morphological, geochemical composition and origins of near-surface atmospheric dust in Changsha city of China

Near-surface atmospheric dust in Changsha city of China was analyzed in terms of morphological and geochemical composition. Morphological and chemical composition of the dust particles were analyzed by environmental scanning electron microscopy coupled with an energy-dispersive X-ray analyzer. Results indicated that the atmospheric dusts were mainly composed of spherule, plate, irregularly shaped and agglomerate, which contains variable sizes and amounts of particles. The dust particles could be categorized into five groups based on their chemical characteristic: Al-, Si-, Ca-, C-rich particles and aggregate. These particles and aggregate could be directly related to nearby polluting activities, such as building construction, traffic emission and coal combustion. The X-ray diffraction results show that the main minerals for atmospheric dust are gypsum, quartz and calcite. Mica, halloysite, montmorillonite, hematite, brushite, zeolite, sepiolite, feldspar, alite, dickite, SiS₂, Fe₆(OH)₂CO₃, FeSO₄, CdSO₄, Pb(NO)₂O₃, Al₂SO₄(OH)₄, As₂O₃SO₃, (NH₄)₂SO₄, NH₄Cl, K(NH₄)·Ca(SO₄)₂·H₂O are also detected in samples. The identification of heavy metals shows that the concentrations of Cr (403.5?mg?kg^?1), Cu (126?mg?kg^?1), Zn (1541.5?mg?kg^?1), Cd (2.5?mg?kg^?1) and Pb (348?mg?kg^?1) in the atmospheric dust are much higher compared to background value of soil. It indicates that the heavy metal (Cr, Cu, Zn, Cd and Pb) in the atmospheric dust is mainly due to human activities. The identification of main sources of atmospheric dust collected in typical areas can help to control the polluting sources in urban area.     

IR photometry and dust-shell models for two carbon stars

We present JHKLM photometry of the carbon stars ST And and T Lyn acquired in 2000–2010. Along with brightness variations due to pulsations, changes on timescales of 2000–3000 days are also observed. Our combined light curves can be satisfactorily represented with light elements derived from visual observations, but the maxima are delayed relative to the calculated times. A color-index analysis demonstrates that the dust shell of ST And is fairly weak, and is manifest only episodically, while the presence of hot dust was always detected for T Lyn. These results confirm models of spherically symmetric stellar dust shells based on mean-flux data, supplemented with observations in the intermediate IR from the IRAS and AKARI satellites. The visual optical depth of the relatively cool dust shell of ST And assuming a dust temperature at the inner edge of T ₁ = 510 K is very low: τ _V = 0.047. The dust shell of T Lyn is considerably hotter (T ₁ = 940 K), with τ _V = 0.95. We estimate the mass-loss rate to be 1.8 × 10⁻⁷ M _⊙/year for ST And and 3.7 × 10⁻⁷ M _⊙/year for T Lyn.     

Chemistry of rainwater in the Massif Central (France): a strontium isotope and major element study

Atmospheric aerosols (sea salt, crustal dust, and biogenic aerosols) are the primary source of dissolved species in rainwater as well as one of the sources of dissolved species in river water. Chemical weathering studies require quantification of this atmospheric input. The crustal component of atmospheric input can have various origins, both distant and local. The proportions of the various inputs (marine, distant or local) are determined in this study.Strontium isotope ratios and Ca, Na, K, Mg, Al, Cl, SO₄, NO₃ and Sr concentrations were measured in rainwater samples collected in the Massif Central (France) over a period of one year. Each sample, collected automatically, represents a monthly series of rain events. Chemical composition of the rainwater samples varied considerably and the ⁸⁷Sr/⁸⁶Sr ratios ranged between 0.709198 and 0.713143.Using Na as an indicator of marine origin, and Al for the crustal input in rain samples, the proportion of marine and crustal elements was estimated from elemental ratios. A marine origin of 4 to 100% of Cl, of 0.6 to 20% of the SO₄, of <1 to 10% of Ca, <1 to 40% of K, 4 to 100% of Mg and 1 to 44% of Sr was determined.Strontium isotopes were used to characterize the crustal sources. The ⁸⁷Sr/⁸⁶Sr ratios of the crustal sources varied considerably from 0.7092 to 0.71625 and indicate the occurrence of multiple sources for the crustal component in the analysed rainwaters.     

Grain size in sediments from Lake Sugan: a possible linkage to dust storm events at the northern margin of the Qinghai–Tibetan Plateau

Samples of surface deposits in the Lake Sugan catchment, as well as surface lake sediments, eolian materials occulted in the lake ice cover, and airborne dust were collected for grain-size analysis. The results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area. Sediment cores were retrieved from Lake Sugan in December 2000, and ²¹⁰Pb and ¹³⁷Cs dating and grain-size analyses were performed on these samples. ²¹⁰Pb ages and the volume percentage of the fraction of lake sediments >63 μm were used to reconstruct the dust storm history from 1957 to 2000. Observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years, suggesting that lake sediments can be employed to trace the dust storm history of the northern Qinghai–Tibetan Plateau.     

松嫩沙地Sr?Nd同位素组成特征

作为亚洲风尘源区的中国北方干旱—半干旱地区的Sr?Nd同位素组成已得到很好的研究,但位于欧亚黄土带最东端的松嫩沙地尚是空白,这影响了对该地区风尘系统的深入理解。为此,系统采集了松嫩沙地19个区域90个河流沙和风成沙样品,并对这些样品进行了分粒级处理（<63 μm、63~30 μm、30~10 μm、<10 μm和<30 μm）。对116个分粒级子样的酸不溶物（硅酸盐组分）进行了Sr?Nd同位素组成的测定。研究结果表明,松嫩沙地可划分出两个大区（嫩江水系和松花江水系）和七个小区,嫩江水系沉积物的Nd同位素组成显著高于松花江水系,而Sr同位素组成明显偏低。松嫩沙地8个剖面纵向上的同位素特征显示,Sr?Nd同位素组成存在“时间效应”,即随时间发生了明显变化,表明了源区地球化学组成的不稳定性。分粒级组成表明,粒度对87Sr/86Sr比值的影响很小,但对Nd同位素组成有明显影响,且存在Nd同位素比值富集在粗颗粒组分中的趋势,这与以往的研究结果不同。无论是地质历史时期还是现在,嫩江水系沉积物（大庆、杜蒙、齐齐哈尔、泰来、白城）对哈尔滨粉尘的贡献都很小。哈尔滨黄土与现代尘暴粉尘有不同的物源,哈尔滨黄土是春季尘暴天气作用的产物,有一个混合源,松花江水系沉积物（扶余、德惠、榆树等地）是哈尔滨黄土的主要粉尘源区,内蒙古中东部的沙地也为哈尔滨黄土贡献了部分的细颗粒粉尘。