Active Dust Sources Research Articles

The Circumglobal Transport of Massive African Dust and Its Impacts on the Regional Circulation in Remote Atmosphere

Abstract Atmospheric dust from North Africa, the largest and most persistently active dust source over the world, spreads widely in the Northern Hemisphere and plays essential roles in the Earth environment evolution. During 7–24 June 2020, an extremely strong dust event occurred with its westward spreading modulated by the North Atlantic Oscillation (NAO) and its eastward spreading regulated by European blocking, ultimately resulting in the circumglobal transport of African dust. The Mediterranean low pressure linked to the European blocking dipole was the key to facilitating the eastward transport of dust. This record-breaking African dust episode caused a notable diurnal precipitation decrease of 0.98 mm day−1 over northeastern India and a decrease of 1.55 mm day−1 over central North America, which was ascribed to the effect of dust-induced radiative heating on large-scale circulation. It triggered a Rossby wave train and caused anomalous high pressure over northeastern India, which weakened the India summer monsoon and consequently inhibited the occurrence of precipitation. Dust-induced radiative heating also supported the stability in the anomalous warm high over North America, further repressing import of moisture from Atlantic. Ambient moisture and atmospheric instability also presented consistent variation over North America and India characterized as strengthen descending motion and sharply reduced moist convection. This study reports, for the first time, the strong modulation of regional circulation by circumglobally transported African dust, especially in Asia and North America. The new aspects on the unexpected consequences on moisture convection indicate broader roles that the dust may play in the global climate change.

Long-term study of desert dust deposition effects on phytoplankton biomass in the Persian Gulf using Google Earth Engine

Persian Gulf is surrounded by the most active dust source regions of the world. Every year, millions of tons of dust are deposited in this area causing significant adverse effects. This research aimed to fill the gap in the field of dust impact quantification regarding different and important regions in the Persian Gulf. We evaluated aerosol optical thickness (AOT) as dust, chlorophyll a (Chl a) as phytoplankton biomass, sea surface temperature (SST), and particulate organic carbon (POC) using Moderate Resolution Imaging Spectroradiometer (MODIS) data to quantify and analyze the impacts of dust. According to dust frequency maps over 21 years, 4 critical regions were selected including the Northern, Central, and Southern regions of the Persian Gulf and Strait of Hormuz. Slightly lower Chl a values were noted in the southern region and Strait of Hormuz compared to the Northern and Central regions. The Mann-Kendall (MK) test and Sen's slope estimator, which can determine trend parameters, were used to analyze 4 selected regions using 8 days, monthly, and yearly averaged data. The results of the MK test showed a significant positive trend for SST and a significant negative trend for POC. AOT and Chl a trends varied based on their locations. The cross-correlation test with a time lag showed maximum correlations between Chl a and dust (AOT) with a delay of 6–7 months. Also, to quantify the impacts of dust on phytoplankton biomass, R2 and analysis of variance (ANOVA) regression were used for data with a 6–7-month time lag. The results showed that the contribution of dust in the amount of Chl a variation was about 10 %–20 %. This study showed that the simultaneous use of remote sensing and statistical methods could provide necessary and timely warnings (regarding management) to prevent algal blooms and aquatic loss in this important and strategic area.

Assessment of potentially toxic elements in atmospheric dust and associated health risks in Zahedan City, Iran.

Zahedan City is situated in the Sistan basin, a highly active dust source region that poses significant risks to human and ecological health due to potentially toxic elements (PTEs) present in atmospheric dust. In this study, we investigated the concentration, sources, and human health risk assessment of PTEs in 88 monthly atmospheric dust samples collected between December 2020 and October 2021 using inductively coupled plasma mass spectrometry. The results showed that the concentrations of PTEs in atmospheric dust followed the descending order of Mn > Zn > Ba > Sr > Cr > V > Ni > Cu > Pb > Co > As > Mo > Cd. The calculated enrichment factors revealed significant enrichment for As > Zn, moderate enrichment Pb > Ni, deficiency to minimal enrichment for Cr > Mn > Fe > Sr > Cd > V > Cu > Ba > Co, and no enrichment for Mo. Arsenic was found to be the major contributor to the potential ecological risk index, accounting for 55% of the total risk. The widespread utilization of arsenic-based pesticides in the surrounding agricultural lands may be a significant contributor to the severe arsenic pollution in the region. The winter season exhibited the highest monthly mean concentrations of Zn and Pb possibly due to temperature inversions trapping local anthropogenic pollutants near the Earth's surface. Cluster analysis revealed a strong correlation between Ni-Cr-Fe-V-Mn-Al, which shows mainly the geogenic source for these elements. The predominant exposure route for non-carcinogenic risk to humans was ingestion. The hazard index (HI) values for the heavy metals studied decreased in the following order: Cr > As > Pb > Ni > Zn > Cu > Cd, for both children and adults. The HI values indicated that there was no possible non-carcinogenic risk associated with exposure to these heavy metals in Zahedan's atmospheric dust. The result of the inhalation cancer risk assessment suggested that while the potential risks of cancer for As, Cd, Cr, and Ni were below the safe level, the levels of Chromium were close enough to the threshold to warrant further investigation and monitoring.

Wind Tunnel Experiments on Volcaniclastic Dust Emission and Dispersion Initiated by Water Droplet Impact

AbstractIceland contains active dust regions within high‐latitude, cold‐climate environments. An abundant supply of particulates <10 μm in diameter (PM10) is available within its extensive glacial outwash plains and through widespread transport and deposition of volcanic ash with hydrophobic tendencies. The climate is notably wetter than dust regions located in hot deserts, so that additional processes governing dust emission must be considered, inclusive of rain splash. Field workers in Iceland report that dust emission events sometimes overlap with precipitation. This study used high‐speed photography in wind tunnel experiments to assess the influence of water droplet impact and wind shear on the detachment and suspension of particulates collected from several active dust source regions within Iceland. Concentrations of PM10 sampled downwind of a single water droplet impact reached values as high as 104 μg m−3 and were positively correlated with increasing wind speed, droplet impact velocity and angle. Our measurements demonstrate that wind shear in a turbulent flow is important for the dispersion of aerosols ejected via water droplet impact from the surface of dry sediment, and that these coincident mechanisms can be highly effective agents of erosion, especially in light winds that are normally incapable of dust entrainment. Foremost, this study provides further evidence of the complexity of dust emission in cold environments and the importance of examining this phenomenon over a wide range of temporal and spatial scale.

The impact of using assimilated Aeolus wind data on regional WRF-Chem dust simulations

Abstract. Land–atmosphere interactions govern the process of dust emission and transport. An accurate depiction of these physical processes within numerical weather prediction models allows for better estimating the spatial and temporal distribution of the dust burden and the characterisation of source and recipient areas. In the presented study, the ECMWF-IFS (European Centre for Medium-Range Weather Forecast – Integrated Forecasting System) outputs, produced with and without the assimilation of Aeolus quality-assured Rayleigh–clear and Mie–cloudy horizontal line-of-sight wind profiles, are used as initial or boundary conditions in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate 2-month periods in the spring and autumn of 2020, focusing on a case study in October. The experiments have been performed over the broader eastern Mediterranean and Middle East (EMME) region, which is frequently subjected to dust transport, as it encompasses some of the most active erodible dust sources. Aerosol- and dust-related model outputs (extinction coefficient, optical depth and concentrations) are qualitatively and quantitatively evaluated against ground- and satellite-based observations. Ground-based columnar and vertically resolved aerosol optical properties are acquired through AERONET sun photometers and PollyXT lidar, while near-surface concentrations are taken from EMEP. Satellite-derived vertical dust and columnar aerosol optical properties are acquired through LIVAS (LIdar climatology of Vertical Aerosol Structure) and MIDAS (ModIs Dust AeroSol), respectively. Overall, in cases of either high or low aerosol loadings, the model predictive skill is improved when WRF-Chem simulations are initialised with the meteorological fields of Aeolus wind profiles assimilated by the IFS. The improvement varies in space and time, with the most significant impact observed during the autumn months in the study region. Comparison with observation datasets saw a remarkable improvement in columnar aerosol optical depths, vertically resolved dust mass concentrations and near-surface particulate concentrations in the assimilated run against the control run. Reductions in model biases, either positive or negative, and an increase in the correlation between simulated and observed values was achieved for October 2020.

Dust sources in Westernmost Asia have a different geochemical fingerprint to those in the Sahara

Dust is an important component of Earth's climate system, directly affecting the global radiation budget and hydrological cycle. The interaction of aerosols with clouds and its impact on regional and global energy budgets remains one of the largest sources of uncertainty in climate model predictions. Records of terrigenous dust accumulation in geological archives also provide a potentially powerful way to assess past changes in hydroclimate. Western Asia, including the Arabian Peninsula, is second only to the Saharan Desert in contributing dust to the global atmosphere. Yet, while satellite-derived maps of dust source activation frequency (DSAF) provide an increasingly granular understanding of the different dust sources within these regions today, our ability to fingerprint their windblown contributions to geological archives is rudimentary, severely limiting the use of dust-based records to reconstruct past changes in continental hydroclimate. A main limitation is a poor understanding of the mineralogical and geochemical composition of the bedrock geology and, more importantly, of the readily deflated unconsolidated sediments in these regions. Here we use published data to produce a DSAF map, centred on the Arabian Peninsula and extending from North Africa to Western Asia (∼40-10 °N; ∼25–65 °E), and we present new radiogenic isotope (Sr and Nd) data from unconsolidated surface sediment samples at active dust-producing sites. We combine our new Sr and Nd data with sparse data on sediments from the literature and the DSAF data to define three new preferential dust source areas (PSAs) in Westernmost Asia: (i) the central belt of the Arabian Peninsula, (ii) the Southern Levant and (iii) Mesopotamia. All three of these PSAs are geochemically distinct from Saharan dust sources. Long-range sediment transport by the Blue Nile and its tributaries, and the Tigris-Euphrates river systems exerts a strong influence on the geochemical fingerprints of dust sources in the Eastern Sahara and Mesopotamia, respectively. The isotopic signature of active dust sources in the central belt of the Arabian Peninsula shows only modest correspondence to underlying bedrock geology suggesting wide scale mixing by aeolian transport internally and/or a weak imprint of palaeo humidity (e.g. localized river reactivation) on dust source composition in comparison to the Eastern Sahara. Our results provide surer foundations for fingerprinting the sources of continental dust accumulating in marine, lacustrine, speleothem and ice archives, an important step in improving our understanding of Quaternary rainfall climate in arguably the most water-stressed region on Earth.

Saharan air outflow variability in the 1980–2020 period

Airborne dust represents a hazard to the environment and human health. The outflow of air masses carrying dust from northern Africa, the world's largest active dust source, to the North Atlantic and Mediterranean regions is modulated by atmospheric conditions. However, how global warming-driven changes on atmospheric circulation have influenced North African air outflow in the recent past is not well understood. Here, we explore the Saharan air outflow from northwestern Africa over the 1980 to 2020 period. We find a decrease in the transport to the Atlantic Ocean and the Iberian Peninsula of −0.29 ± 0.16% dec−1 and -0.66 ± 0.18% dec−1, respectively, and an increasing trend to the Mediterranean Sea (0.24 ± 0.18% dec−1) and Europe (0.60 ± 0.18% dec−1). The results indicate that the strengthening of the Atlantic high pressure system and the Saharan thermal low, both associated with the narrowing of the Intertropical Convergence Zone and the Hadley Cell expansion under global warming, could be favoring the Saharan outflow to the Mediterranean Sea and Europe in detriment of transport to the Atlantic Ocean. The results also show that present-day Saharan air arrives at these regions at higher altitudes and in shorter timescales than decades ago. This is associated to the increase in surface heating conditions in the Sahara, 0.41 ± 0.02 °C dec−1, that can inject air into windier upper atmospheric levels, thereby allowing higher and faster air transport. Our results suggest a change in the Saharan air outflow likely associated with global warming and with potentially significant implications for the temporal and spatial patterns of North African dust export.

The natural reduction of threat in selected systems of old buildings containing asbestos

The aim of this study was to measure changes in asbestos dust concentrations over extended use in old building systems. Buildings from different systems during their service lifetimes and after asbestos removal were tested. Asbestos dust concentrations decreased in all building systems due to air exchange and other phenomena in the absence of new active dust sources. Currently, with proper use of those buildings, average values of dust concentrations did not exceed 300–400 f/m3 with a downward trend to < 300 f/m3. The results of these studies were obtained with a modified optical microscopy technique, verified by SEM and TEM methods. The graphical trends in concentration changes over longer periods illustrate the potency of opposing factors reducing and increasing indoor air pollution. If removal asbestos work was not carried out carefully, single measurements conducted in the short-term and mandated immediately after asbestos removal may not detect hazards that appear over time. Monitoring buildings over longer periods allows detection of significant contamination changes. In many cases, the minimal air contamination undermines the desirability of removing asbestos in old buildings.

Dust source susceptibility mapping in Tigris and Euphrates basin using remotely sensed imagery

The present study aims to develop an applicable, robust, and generalizable approach building on the integration of machine learning classifiers into dust source susceptibility mapping. Five machine learning classifiers were used for this purpose, including Support Vector Machine, Random Forest, Naïve Bayes, Logistic Regression, and Artificial Neural Network. The study area includes the Tigris-Euphrates river basin, considered one of the world’s largest active dust sources during the last two decades. A total of 411 active dust sources (i.e. hotspots) were identified as ground truth via visual interpretation of sub-daily MODIS-Terra/Aqua time-series imagery from 2000 to 2020 and then used to train and validate the classifiers. The main environmental drivers of dust formation were incorporated based on remote sensing data/products, including Tasseled Cap components, Soil Crust Index, Modified Fournier Index, and the Sentinel-5 Absorbing Aerosol Index. Dempster-Shafer (D-S) theory was used to merge the results from all classifiers to obtain an accurate susceptible dust sources map of the region. Each of the five classifiers and the final integrated D-S model were assessed using the ROC curve, AUC, and Calibration Plot. The mean prediction accuracy of all five classifiers was 87.7% and 86.3% for dust sources susceptible and non-susceptible classes, respectively. The D-S increased the classification accuracy in susceptible and non-susceptible classes by 7.5% and 12.6%, respectively. Finally, the wind erosion thresholds, as a limiting environmental factor in the emission of dust, were applied over the D-S-based susceptible dust sources map to measure the degree of susceptibility in the identified dust sources.

Characterization of dust activation and their prevailing transport over East Asia based on multi-satellite observations

Mineral dust from the deserts and arid areas in East Asia plays a critical role in regional climate and air quality. Based on integrated satellite observations and MERRA-2 reanalysis, we provide an observational insight into dust activities governing spatial patterns of dust aerosols over East Asia. With Moderate resolution Imaging Spectroradiometer Aerosol Optical Depth (AOD) and Ozone Monitoring Ultraviolet Aerosol Index (UVAI), fixed dust-active areas with distinct spatial-temporal differences are revealed. Besides the few dust storms mostly in spring, unnoticeable but frequent dust plumes are found to be the predominant sources of prevailing dust particles over East Asia. Compared with the active dust sources in Taklimakan Desert throughout the year, dust activities in Gobi deserts are at a much lower frequency. The elevated dust plumes are concentrated within 2–6 km over the deserts with large seasonal variations, and can be transported downstream to eastern China and Sichuan Basin within 3–5 days. Moreover, owing to the lack of enough strong winds, these dust plumes tend to be concentrated above the haze layers near surface in eastern China. The intense temperature inversion during winter and early spring can delay the mixing of dust-pollution. Despite a generally reasonable performance in dust AOD, MERRA-2 reanalysis exhibits some uncertainties in reproducing spatial locations of dust hotspots, dust concentration, and transport process. Our results emphasize significant role of the inapparent but prevalent dust plumes in air quality and in climate effects of East Asia.

The Discovery of African Dust Transport to the Western Hemisphere and the Saharan Air Layer: A History

AbstractThere is great interest in wind-borne mineral dust because of the role that dust plays in climate by modulating solar radiation and cloud properties. Today, much research focuses on North Africa because it is Earth’s largest and most persistently active dust source. Moreover, this region is expected to be greatly impacted by climate change, which would affect dust emission rates. Interest in dust was stimulated over 50 years ago when it was discovered that African dust was frequently transported across the Atlantic in great quantities. Here we report on the initial discovery of African dust in the Caribbean Basin. We show that there were three independent “first” discoveries of African dust in the 1950s through the 1960s. In each case, the discoverers were not seeking dust but, rather, they had other research objectives. The meteorological context of African dust transport was first elucidated in 1969 with the characterization of the Saharan air layer (SAL) and its role in effecting the efficient transport of African dust over great distances to the Western Hemisphere. The link between dust transport and African climate was established in the 1970s and 1980s when dust transport to the Caribbean increased greatly following the onset of severe drought in the Sahel. Here we chronicle these events and show how they contributed to our current state of knowledge.

Tracking prevailing dust aerosol over the air pollution in central China with integrated satellite and ground observations

Besides intense dust storms, downstream transport of dust particles in the extensive deserts of East Asia have been rarely concerned. In this study, we present a comprehensive insight into sources, transport process, and potential influence of the prevalent dust particles in central China during October 2020 based on integrated satellite and ground observations. Although dust events are usually considered concentrated in spring, satellite observations show that dust sources are active during fall. Thick dust layers with high uplifted altitudes at ~5 km are found in their downstream path, which can be carried to northern China and even the Sichuan Basin by predominant northwestern winds at 700 hPa. Despite a lack of air masses directly from active dust sources, dust plumes from both Taklimakan Desert and Gobi deserts can be blown to central China in their transport path or when they have arrived over northern and eastern China. Unlike dust storms with strong winds cleaning local atmospheric pollutants, these floating dust plumes tend to suspend over the air pollution near surface. In particular, the slow dust-pollution mixing process in central China can last for as long as ~3–4 days due largely to the common temperature inversion in fall. Despite a dominant contribution (>50%) in particle pollution, these dust transport with much smaller scales than dust storms can be unnoticeable. Our results suggest that more attention should be paid to the role of these unnoticeable but frequent dust plumes in regional atmospheric environment and climate effects.

Water bodies changes in Tigris and Euphrates basin has impacted dust storms phenomena

Abstract The Tigris and Euphrates basin (TEB) has long been one of the active dust sources in the Middle East. In the last four decades, inefficient water resources management has intensified dust activities in the TEB. Dried water bodies have a high potential for dust emission. Therefore, several studies have been conducted in TEB to identifying dust sources. Nevertheless, the role of water body changes in dust emission is not yet clear. The present study aimed to evaluate the effect of natural and anthropogenic drivers on changes in water bodies and dust emissions. The long-term spatial-temporal monitoring of water bodies changes was performed using 36-year Landsat 5, 7, and 8 multi-spectral images. Using visual interpretation of MODIS-RGB143 images, 904 dust storm events were identified, about 61% of them originated from dried beds of lakes, marshlands, and river margins. The lowest area of water bodies was observed in the period from 2000 to 2004 and 2008 to 2012. The area of water bodies in the two mentioned periods has decreased by 31% and 33%, respectively. Severe droughts have occurred in the region during these two periods. Overall, this has led to an increase of almost 23% in dust activities. However, the relationship between change in the area of water bodies and dust emission in the TEB is not necessarily linear and straightforward. In general, it can be concluded that the dried beds of water bodies is the largest source of dust emission in the TEB.

Wind Tunnel‐Based Comparison of PM10 Emission Rates for Volcanic Ash and Glaciogenic Aerosol Sources Within Iceland

AbstractIceland contributes 30–40 million tons of mineral dust to the atmosphere each year. Emission events are linked to exceedingly high concentrations of PM10, poor air quality, and respiratory disease, particularly in Reykjavík. Volcaniclastic aerosols have unique microphysical properties, and usually are porous and highly angular, with large surface areas bearing ultrafine, nanoscale dustcoats. The large internal void space contributes to low particle density, believed to affect emission and deposition rates in the atmospheric boundary layer, as well as the range of transport. However, the aerodynamic and sedimentological factors that govern dust entrainment in these high‐latitude settings are not well constrained empirically, providing little guidance for the parameterization of aerosol dispersion models. A series of laboratory wind tunnel simulations were carried out under full climate control to evaluate these effects for Icelandic samples collected from five active dust sources, inclusive of volcanic ash and glaciofluvial sediments. PM10 emission rates measured in this study are similar in magnitude to those obtained in a small number of field studies within selected high‐latitude regions, and for volcanic ash using a PI‐SWERL. The scaling with friction velocity is well described by the 1988 dust emission model of Gillette and Passi, while the parameterization appears to be strongly dependent on the median particle size. Sediments from the coarsest Icelandic dust sources were found to be most emissive, owing to the importance of particle impact, while the proportionate amount of PM10 within the test bed was not found to correlate with the emission rate.

North African mineral dust sources: new insights from a combined analysis based on 3D dust aerosol distributions, surface winds and ancillary soil parameters

Abstract. Mineral dust aerosol is a key player in the climate system. Determining dust sources and the spatio-temporal variability of dust emission fluxes is essential for estimating the impact of dust on the atmospheric radiation budget, cloud and precipitation formation processes, the bio-productivity and, ultimately, the carbon cycle. Although much effort has been put into determining dust sources from satellite observations, geo-locating active dust sources is still challenging and uncertainties in space and time are evident. One major source of uncertainty is the lack of clear differentiation between near-source dust aerosol and transported dust aerosol. In order to reduce this uncertainty, we use 3D information on the distribution of dust aerosol suspended in the atmosphere calculated from spectral measurements obtained by the Infrared Atmospheric Sounding Interferometer (IASI) by using the Mineral Aerosols Profiling from Infrared Radiance (MAPIR) algorithm. In addition to standard dust products from satellite observations, which provide 2D information on the horizontal distribution of dust, MAPIR allows for the retrieval of additional information on the vertical distribution of dust plumes. This ultimately enables us to separate between near-source and transported dust plumes. Combined with information on near-surface wind speed and surface properties, low-altitude dust plumes can be assigned to dust emission events and low-altitude transport regimes can be excluded. Consequently, this technique will reduce the uncertainty in automatically geo-locating active dust sources. The findings of our study illustrate the spatio-temporal distribution of North African dust sources based on 9 years of data, allowing for the observation of a full seasonal cycle of dust emissions, differentiating morning and afternoon/evening emissions and providing a first glance at long-term changes. In addition, we compare the results of this new method to the results from Schepanski et al. (2012), who manually identified dust sources from Spinning Enhanced Visible and InfraRed Imager (SEVIRI) red–green–blue (RGB) images. The comparison illustrates that each method has its strengths and weaknesses that must be taken into account when using the results. This study is of particular importance for understanding future environmental changes due to a changing climate.

The Use of Aerosol Optical Properties in Identification of Dust Sources in Iraq

In recent years, dust events in Iraq become very frequent due to its emission from active local dust sources or transportation from abroad. This study aims to identify dust sources in Iraq for the period (1st January, 2005 to 31 December, 2016) using mean of monthly mean of the aerosol optical properties including Deep Blue Aerosol Optical Depth(DB-AOD), Deep Blue Angstrom Exponent(DB-AE) and UV Positive Absorption Aerosol Index(AAI) acquired from space borne instruments including MODerate resolution Imaging Spectroradiometer (MODIS) for both Aqua and Terra, Multiangle Imaging SpectroRadiometer (MISR) and Ozone Monitoring Instrument (OMI), considering the dust aerosols having values of AOD>0.5, AE<0.5 and AI>0.7 based on the predefined thresholds. The results show that Al-Jazira and the southern region of Iraq considered as significant dust sources most of the year, with the absence of active dust sources in December, January, October and November. While spring and summer months show many active dust sources in the Alluvial plain, western plateau, southern and southeastern parts of Iraq with high AOD, low AE and high AAI especially in April, May, June and July. MISR/AOD shows lower values of MODIS-DB in Iraq along months of the years, which could be due to the insufficient coverage over dust regional sources compared to MODIS.

Three North African dust source areas and their geochemical fingerprint

North Africa produces more than half of the world's atmospheric dust load. Once entrained into the atmosphere, this dust poses a human health hazard locally. It also modifies the radiative budget regionally, and supplies nutrients that fuel primary productivity across the North Atlantic Ocean and as far afield as the Amazonian Basin. Dust accumulation in deep sea and lacustrine sediments also provides a means to study changes in palaeoclimate, particularly those associated with rainfall climate change. Systematic analysis of satellite imagery has greatly improved our understanding of the trajectories of long-range North African dust plumes, but our knowledge of the dust-producing source regions and our ability to fingerprint their contribution to these export routes is surprisingly limited. Here we report new radiogenic isotope (Sr and Nd) data for sediment samples from known dust-producing substrates (dried river and lake beds), integrate them with published isotope data and weight them for dust source activation. We define three isotopically distinct preferential dust source areas (PSAs): a Western, a Central and an Eastern North African PSA. More data are needed, particularly from the Western PSA, but our results show a change in PSA dust source composition to more radiogenic Nd- and less radiogenic Sr-isotope values from west to east, in line with the overall decreasing age of the underlying bedrock. Our data reveal extreme isotopic heterogeneity within the Chadian region of the Central PSA, including an extremely distinctive geochemical fingerprint feeding the Bodélé Depression, the most active dust source on Earth. Our new analysis significantly improves the reliability by which windblown dust deposits can be geochemically fingerprinted to their distant source regions.

Laboratory Investigation of Particle‐Scale Factors Affecting the Settling Velocity of Volcaniclastic Dust

AbstractIceland contains some of the largest and most active dust sources in the Arctic, with the frequency of major emission events increasing in the wake of catastrophic volcanic eruptions, such as the 2010 Eyjafjallajökull eruption. Relatively juvenile Icelandic volcaniclastic dust particles are porous and highly angular, and they frequently bear ultrafine nanoscale dustcoats. Their low density is speculated to affect deposition rates in the atmosphere, while substantial amounts of water adsorbed onto their expansive surface area may affect nucleation, aggregation, and settling. Using a 2‐D laser Doppler anemometer, the present paper reports on a set of highly controlled fall column experiments designed to evaluate the dependency of the settling velocity upon particle morphology (e.g., size, shape, density, and surface area) and relative humidity (RH). Measurements for samples obtained from four Icelandic field sites are compared to those for solid glass spheres of similar diameter. The results confirm that the amount of adsorbed water increases with RH and the particle specific surface area. Higher dust concentrations are found to favor particle interaction and the formation of aggregates, especially at higher RH. Under dry conditions (20 % &lt; RH &lt; 30 % ), the horizontal drift velocity measured for the angular, porous Icelandic particles exceeds that observed for solid glass spheres, although these measurements are an order of magnitude smaller than the vertical velocity. As compared to particle diameter, shape does not appear to influence either the settling rate or drag coefficient at Reynolds numbers ≤10−2, owing to the dominance of viscous effects over form drag.

Evaluating temporal and spatial variability and trend of aerosol optical depth (550 nm) over Iran using data from MODIS on board the Terra and Aqua satellites

Our knowledge of the temporal-spatial variations of atmospheric aerosols is necessary because they can affect public health and air quality. This paper studied Collection 6, the product of Aerosol Optical Depth (AOD 550 nm), using the Deep Blue algorithm of moderate-resolution imaging spectroradiometer (MODIS) on board the Terra and Aqua satellites over Iran from 2003 to 2017. Long-term data of the dust using synoptic stations were also used. The results showed that the southwestern Iran, the Persian Gulf coast from Bushehr to Bandar Abbas, and the Makran coastal area in southeastern Iran have the highest seasonal means of Aerosol optical depth (AOD > 0.3) and that they are among the aerosol hotspot areas in southwestern Asia. Other regions in Iran, especially the northwest and the Zagros Mountains, have the lowest aerosol optical depth (AOD < 0.04). The highest AOD amount of Terra (0.144) and Aqua (0.156) occurs in the spring, and the lowest amount occurs in the autumn season (0.094 and 0.101 Terra and Aqua, respectively). The heights act as a barrier on the particle transport pathway and, as a result, will affect the release of dust on local and regional scales. AOD increase in Iran is more related to aerosol loading in deserts and arid areas around the country. The AOD increase during the cold period of the year in industrial cities is due to the combustion of fossil fuels and the reduction of the boundary layer height (BLH). It is because most atmospheric pollutants are released in the boundary layer and are homogenized through turbulent mixed layer processes. The most prominent active dust sources around Iran, which are the main source of aerosol increase, can be categorized into four sources: (1) Mesopotamian, (2) Northern Arabian Peninsula, (3) Elrob Elkhali desert, and (4) East Arabian Peninsula. The AOD seasonal trend showed that the most significant increasing trend occurs in autumn on the TERRA (42.82%) and Aqua (32.32%) satellites. The largest decreasing trend of AOD in Iran is observed in winter in Kermanshah province (− 0.0011 year−1) in western Iran and in other seasons in southeastern Iran for which meteorological changes play a major role.

Assessment of a new detection threshold for [formula omitted] concentrations linked to African dust events in the Caribbean Basin

The Lesser Antilles is an intermediate zone located between the Caribbean Sea and the Atlantic Ocean. This area is frequently affected by the major long range Saharan dust transportation from West African desert sources. The aerosols optical properties are provided by the AEronet Robotic NETwork (AERONET) measurement sites in Puerto Rico, Guadeloupe, and Barbados. Thus, Aerosols Optical Depth (AOD), Angstrom Exponent (AE), Volume Particle Size Distribution (VPSD), complex refractive indexes, and Single Scattering Albedo (SSA) were used to define the predominant type of atmospheric particles namely sea salt aerosols, mineral dust or aerosols mixture. Obtained results show that aerosols in the atmospheric column (AOD) and surface dust measurements (PM10) are well correlated with correlation coefficients of 0.72 and 0.81 respectively for Puerto Rico, and Guadeloupe. Detailed analysis of optical data associated to daily PM10 concentrations highlighted that dust phenomenon can be observable below PM10 threshold of 50 μg∕m3 given by the European directives to detect dust episodes. Indeed, for Caribbean islands, episodes of desert dust phenomenon have been detected from 35 μg∕m3. The climatological assessment of monthly dust events observed in Puerto Rico, Guadeloupe, and Martinique between 2006 and 2016 highlighted a low dust season from November to February and a high dust season from May to August. Both seasons are separated by two transition dust periods: March to April and September to October. Lastly, the day-to-day back trajectories (NOAA-HYSPLIT) illustrated the general atmospheric circulation and show three main dust transportation routes: the North West African Path (62.7%); the South West African Path (20.8%) ; and the North East Atlantic Path (15.1%). By computing the average PM10 concentrations bring from each path, we notice that South West African Path is the most loaded in mineral dust because he comes from one of the most persistently active and intense dust sources in the world, i.e. Bodélé Depression in northern Chad.