Search

The direct radiative forcing efficiency of dust aerosol (DRFE dust) is an important indicator to measure the climate effect of dust. The DRFE dust is determined by the microphysical properties of dust, which vary with dust source regions. However, there are only sparse in situ measurements of them, such as the distribution of the dust aerosol particle size and the complex refractive index in the main dust source regions. Furthermore, recent studies have shown that the non-spherical effect of the dust particle is not negligible. The DRFE dust is often evaluated by estimating given microphysical properties of the dust aerosols in the radiative transfer model (RTM). However, considerable uncertainties exist due to the complex and variable dust properties, including the complex refractive index and the shape of the dust. The DRFE dust over the Taklimakan Desert and Sahara is derived from the satellite observations in this paper. The advantage of the proposed satellite-based method is that there is no need to consider the microphysical properties of the dust aerosols in estimating the DRFE dust. For comparison, the observed DRFE dust is compared with that simulated by the RTM. The differences in the dust microphysical properties in these two regions and their impacts on DRFE dust are analyzed. The DRFE dust derived from the satellite observation is -39.6±10.0 W m -2τ-1 in March 2019 over Tamanrasset in the Sahara and -48.6±13.7 W m -2τ-1 in April 2019 over Kashi in the Taklimakan Desert. According to the analyses of their microphysical properties and optical properties, the dust aerosols from the Taklimakan Desert (Kashi) scatter strongly. The RTM-simulated results (-41.5 to -47.4 W m -2τ-1 over Kashi and - 32.2 to - 44.3 W m -2τ-1 over Tamanrasset) are in good agreement with the results estimated by satellite observations. According to previous studies, the results in this paper are proven to be reasonable and reliable. The results also show that the microphysical properties of the dust can significantly influence the DRFE dust. The satellite-derived results can represent the influence of the dust microphysical properties on the DRFE dust , which can also validate the direct radiative effect of the dust aerosol and the DRFE dust derived from the numerical model more directly. [ABSTRACT FROM AUTHOR]

In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and -5 ∘ C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µ m). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about -10 ∘ C, the zone in which the first ice was observed in these clouds. The small ice particles were observed to grow rapidly by vapour diffusion, riming, and possibly through collisions with supercooled raindrops, causing these to freeze and potentially shatter. This in turn leads to the further production of secondary ice in these clouds. Hence, although the numbers of primary ice particles are small, they are very effective in initiating the rapid glaciation of the cloud, altering the dynamics and precipitation production processes. [ABSTRACT FROM AUTHOR]

In this paper, a long-term large-scale Saharan dust transport event which occurred between 14 and 27 June 2020 is tracked with the spaceborne lidars ALADIN (Atmospheric Laser Doppler Instrument) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) together with ECMWF (European Centre for Medium-Range Forecasts) and HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory model) analysis. We evaluate the performance of ALADIN and CALIOP on the observations of dust optical properties and wind fields and explore the possibility of tracking the dust events and calculating the dust mass advection with the combination of satellite and model data. The dust plumes are identified with the AIRS/Aqua Dust Score Index and with the vertical feature mask product from CALIOP. The emission, dispersion, transport and deposition of the dust event are monitored using the data from AIRS/Aqua, CALIOP and HYSPLIT. With the quasi-synchronized observations by ALADIN and CALIOP, combined with the wind field and relative humidity, the dust advection values are calculated. From this study, it is found that the dust event generated on 14 and 15 June 2020 from the Sahara in North Africa dispersed and moved westward over the Atlantic Ocean, finally being deposited in the western Atlantic Ocean, the Americas and the Caribbean Sea. During the transport and deposition processes, the dust plumes are trapped in the northeasterly trade-wind zone between latitudes of 5∘ and 30∘ N and altitudes of 0 and 6 km. Aeolus provided the observations of the dynamics of this dust transport event in the Saharan Air Layer (SAL). From the measurement results on 19 June 2020, the dust plumes are captured quasi-simultaneously over the emission region (Western Sahara), the transport region (middle Atlantic) and the deposition region (western Atlantic) individually, which indicates that the dust plume area over the Atlantic on the morning of this day is quite enormous and that this dust transport event is massive and extensive. The quasi-synchronization observation results of 15, 16, 19, 24 and 27 June by ALADIN and CALIOP during the entire transport process show good agreement with the Dust Score Index data and the HYSPLIT trajectories, which indicates that the transport process of the same dust event is tracked by ALADIN and CALIOP, verifies that the dust transport spent around 2 weeks from the emission to the deposition and achieved the respective observations of this dust event's emission phase, development phase, transport phase, descent phase and deposition phase. Finally, the advection values for different dust parts and heights on 19 June and on the entire transport routine during transportation are computed. On 19 June, the mean dust advection values are about 1.91±1.21 mg m -2 s -1 over the emission region, 1.38±1.28 mg m -2 s -1 over the transport region and 0.75±0.68mgm-2s-1 over the deposition region. In the whole lifetime of the dust event, the mean dust advection values were about 1.51±1.03mgm-2s-1 on 15 June 2020, 2.19±1.72mgm-2s-1 on 16 June 2020, 1.38±1.28mgm-2s-1 on 19 June 2020, 1.60±1.08mgm-2s-1 on 24 June 2020 and 1.03±0.60mgm-2s-1 on 27 June 2020. During the dust development stage, the mean advection values gradually increased and reached their maximum on 16 June with the enhancement of the dust event. Then, the mean advection values decreased during the transport and the deposition of the dust over the Atlantic Ocean, the Americas and the Caribbean Sea. [ABSTRACT FROM AUTHOR]

This paper answers the question: How can a region as small as the Bodélé Depression continuously supply large amounts of dust to the Amazon Basin? To answer this question, you must know that millions of tons of dust to fly over more than 4000 km must first be lifted into the upper atmosphere. Such a criterion can only be satisfied by the existence of very violent winds that last several days. This condition was dictated by the geography and geomorphology of the Bodélé region. The adequate layout of the Tibesti and Ennedi mega-obstacles upstream of the Bodélé offers the most beautiful Venturi on the planet. In a very rare case, 3 pass areas participate at the same time to increase the wind speed. These are the passes of Tibesti (south-east), Ennedi (northwest) and Bembéché (under the Venturi effect). The harmattan wind from Libya and Egypt rushes into the Borkou tunnel and escapes from Bembéché (the pass) with much greater speed. The detachment of the air streams from the obstacles takes place in the detachment area (Largeau), which is accompanied by gigantic vortices, thus lifting the dust into the atmosphere. Thus, during the last 20 years, approximately 503 dust uplifts have been recorded at the level of the Bodélé depression, i.e., 58% of the total number of uplifts recorded in the Sahara. The great storms we have called effective upheavals. These are long-lasting dust lifts that exceed 7 days. These storms can send fine particles toward the Amazon. Each year, 2 to 3 effective uprisings per year are recorded in the Bodélé depression. [ABSTRACT FROM AUTHOR]

This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over southern Europe in late March 2020 (27–30 March 2020). This event was associated with an anomalous circulation pattern leading to several days of PM 10 (particulate matter with an aerodynamic diameter less than 10 µ m) exceedances in connection with a dust source located in central Asia; this is a rare source of dust for Europe, which is more frequently affected by dust outbreaks from the Sahara Desert. The synoptic meteorological configuration was analyzed in detail, and the aerosol evolution during the transit of the dust plume over northern Italy was assessed at high time resolution by means of optical particle counting at three stations, namely Bologna, Trieste, and Mt. Cimone, allowing for the revelation of the transport timing among the three locations. Back-trajectory analyses supported by Copernicus Atmosphere Monitoring Service (CAMS) maps allowed for the location of the mineral dust source area in the Aralkum region. Therefore, the event was analyzed by observing the particle number size distribution with the support of chemical composition analysis. It is shown that the PM 10 exceedance recorded is associated with a large fraction of coarse particles, which is in agreement with mineral dust properties. Both the in situ number size distribution and the vertical distribution of the dust plume were cross-checked using lidar ceilometer and aerosol optical depth (AOD) data from two nearby stations and showed that the dust plume (in contrast to those originating from the Sahara Desert) traveled close to the ground (up to a height of about 2 km). The limited mixing layer height caused by high concentrations of absorbing and scattering aerosols caused the mixing of mineral dust with other locally produced ambient aerosols, thereby potentially increasing its morbidity effects. [ABSTRACT FROM AUTHOR]

This paper deals with the mechanism of the uplift of dust from the Sahara in the atmosphere. The first study carried out in 2001 showed that it is at the level of the megaobstacles of the Sahara that the wind dynamics are very active. So, if there is dust rising, it will be at the level of these rock masses. To answer these hypotheses, we used satellite images taken over the Sahara during the period: 2001-2021. The results obtained showed that the Sahara recorded about 875 dust lifts during the period: 2001-2021. It is these uplifts that can send dust flying over the Atlantic. The years 2017 and 2020 recorded the highest number of dust lifts exceeding 600 days. Three types of dust lifting were highlighted: weak (Duration < 3 days), medium (7 days > duration = 3 days) and strong (Duration = 7 days). We have defined effective uplift as uplift capable of propelling a significant amount of dust into the atmosphere. A map of dust lifting areas in the Sahara has been established. Three foci of dust risings in the Sahara have been located. These are the areas induced by the mega-obstacles: Hoggar-Tassili N'Ajjer (Algeria), Aïr (Niger) as well as Tibesti and Ennedi (Chad). [ABSTRACT FROM AUTHOR]

Infrared "Desert Dust" composite imagery taken by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), onboard the Meteosat Second Generation (MSG) series of satellites above the equatorial East Atlantic, has been widely used for more than a decade to identify and track the presence of dust storms from and over the Sahara Desert, the Middle East, and southern Africa. Dust is characterised by distinctive pink colours in the Desert Dust false-colour imagery; however, the precise colour is influenced by numerous environmental properties, such as the surface thermal emissivity and skin temperature, the atmospheric water vapour content, the quantity and height of dust in the atmosphere, and the infrared optical properties of the dust itself. For this paper, simulations of SEVIRI infrared measurements and imagery have been performed using a modelling system, which combines dust concentrations simulated by the aerosol transport model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) with radiative transfer simulations from the RTTOV (Radiative Transfer for TOVS) model. Investigating the sensitivity of the synthetic infrared imagery to the environmental properties over a 6-month summertime period from 2011 to 2013, it is confirmed that water vapour is a major control on the apparent colour of dust, obscuring its presence when the moisture content is high. Of the three SEVIRI channels used in the imagery (8.7, 10.8, and 12.0 µm), the channel at 10.8 µm has the highest atmospheric transmittance and is therefore the most sensitive to the surface skin temperature. A direct consequence of this sensitivity is that the background desert surface exhibits a strong diurnal cycle in colour, with light blue colours possible during the day and purple hues prevalent at night. In dusty scenes, the clearest pink colours arise from high-altitude dust in dry atmospheres. Elevated dust influences the dust colour primarily by reducing the contrast in atmospheric transmittance above the dust layer between the SEVIRI channels at 10.8 and 12.0 µm , thereby boosting red and pink colours in the imagery. Hence, the higher the dust altitude, the higher the threshold column moisture needed for dust to be obscured in the imagery: for a sample of dust simulated to have an aerosol optical depth (AOD) at 550 nm of 2–3 at an altitude of 3–4 km, the characteristic colour of the dust may only be impaired when the total column water vapour is particularly moist (⪆39 mm). Meanwhile, dust close to the surface (altitude <1 km) is only likely to be apparent when the atmosphere is particularly dry and when the surface is particularly hot, requiring column moisture ⪅13 mm and skin temperatures ⪆314 K, and is highly unlikely to be apparent when the skin temperature is ⪅300 K. Such low-altitude dust will regularly be almost invisible within the imagery, since it will usually be beneath much of the atmospheric water vapour column. It is clear that the interpretation of satellite-derived dust imagery is greatly aided by knowledge of the background environment. [ABSTRACT FROM AUTHOR]

Mineralogical composition drives dust impacts on Earth's climate systems. However, most climate models still use homogeneous dust, without accounting for the temporal and spatial variation in mineralogy. To quantify the radiative impact of resolving dust mineralogy on Earth's climate, we implement and simulate the distribution of dust minerals (i.e., illite, kaolinite, smectite, hematite, calcite, feldspar, quartz, and gypsum) from Claquin et al. (1999) (C1999) and activate their interaction with radiation in the GFDL AM4.0 model. Resolving mineralogy reduces dust absorption compared to the homogeneous dust used in the standard GFDL AM4.0 model that assumes a globally uniform hematite volume content of 2.7 % (HD27). The reduction in dust absorption results in improved agreement with observation-based single-scattering albedo (SSA), radiative fluxes from CERES (the Clouds and the Earth's Radiant Energy System), and land surface temperature from the CRU (Climatic Research Unit) compared to the baseline HD27 model version. It also results in distinct radiative impacts on Earth's climate over North Africa. Over the 19-year (from 2001 to 2019) modeled period during JJA (June–July–August), the reduction in dust absorption in AM4.0 leads to a reduction of over 50 % in net downward radiation across the Sahara and approximately 20 % over the Sahel at the top of the atmosphere (TOA) compared to the baseline HD27 model version. The reduced dust absorption weakens the atmospheric warming effect of dust aerosols and leads to an alteration in land surface temperature, resulting in a decrease of 0.66 K over the Sahara and an increase of 0.7 K over the Sahel. The less warming in the atmosphere suppresses ascent and weakens the monsoon inflow from the Gulf of Guinea. This brings less moisture to the Sahel, which combined with decreased ascent induces a reduction of precipitation. To isolate the effect of reduced absorption compared to resolving spatial and temporal mineralogy, we carry out a simulation where the hematite volume content of homogeneous dust is reduced from 2.7 % to 0.9 % (HD09). The dust absorption (e.g., single-scattering albedo) of HD09 is comparable to that of the mineralogically speciated model on a global mean scale, albeit with a lower spatial variation that arises solely from particle size. Comparison of the two models indicates that the spatial inhomogeneity in dust absorption resulting from resolving mineralogy does not have significant impacts on Earth's radiation and climate, provided there is a similar level of dust absorption on a global mean scale before and after resolving dust mineralogy. However, uncertainties related to emission and distribution of minerals may blur the advantages of resolving minerals to study their impact on radiation, cloud properties, ocean biogeochemistry, air quality, and photochemistry. On the other hand, lumping together clay minerals (i.e., illite, kaolinite, and smectite), but excluding externally mixed hematite and gypsum, appears to provide both computational efficiency and relative accuracy. Nevertheless, for specific research, it may be necessary to fully resolve mineralogy to achieve accuracy. [ABSTRACT FROM AUTHOR]

High desert dust concentrations raise concerns about adverse health effects on human populations. Based on a systematic literature review, this paper aims to learn more about the relationship between desert dust and human health in the world and to analyse the place of West Africa as a study area of interest. Papers focussing on the potential relationship between dust and health and showing quantitative analyses, published between January 1999 and September 2011, were identified using the ISI Web of Knowledge database ( N = 50). A number of adverse health effects, including respiratory, cardiovascular and cardiopulmonary diseases, are associated with dust. This survey highlights obvious dust impacts on human health independently of the study area, health outcomes and method. Moreover, it reveals an imbalance between the areas most exposed to dust and the areas most studied in terms of health effects. None of these studies has been conducted in West Africa, despite the proximity of the Sahara, which produces about half of the yearly global mineral dust. In view of the alarming results in many parts of the world (Asia, Europe, America), this paper concludes by stressing the importance of carrying out impact studies of Saharan dust in West Africa, where dust events are more frequent and intense than anywhere else. [ABSTRACT FROM AUTHOR]

Massive amounts of Saharan dust are blown from the coast of northern Africa across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate which include reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between north-west Africa and the Caribbean along 12° N, in a downwind extension of the land-based dust collectors placed at 19° N on the Mauritanian coast in Iouîk. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronized intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the downwind sediment trap sites, and with satellite observations of Saharan dust outbreaks. First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iouîk. Downwind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic Ocean, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended, with autonomous dust sampling buoys for better quantification of Saharan dust transport and deposition from source to sink and their impact on fertilization and carbon export to the deep ocean. [ABSTRACT FROM AUTHOR]

Coarse mineral dust particles have been observed much further from the Sahara than expected based on theory. They have different impacts to finer particles on the Earth's radiative budget, and carbon and hydrological cycles, though tend to be under-represented in climate models. We use measurements of the full dust size distribution from aircraft campaigns over the Sahara, Canaries, Cape Verde and Caribbean. We assess the observed and modelled dust size distribution over long-range transport at high vertical resolution using the Met Office Unified Model, which represents dust up to 63.2 μ m diameter, greater than most climate models. In the observations, we find that the mass contribution of coarse particles (d>6.32 μ m) to total mass is independent of 0.55 μ m aerosol optical depth. We show that the model generally replicates the vertical distribution of the total dust mass but transports larger dust particles too low in the atmosphere. Importantly, coarse particles in the model are deposited too quickly, resulting in an underestimation of dust mass that is exacerbated with westwards transport; 20–63 μ m dust mass contribution between 2–3.7 km altitude is underestimated by factors of up to 11 at the Sahara, 150 at the Canaries and 340 at Cape Verde. At the Caribbean, there is negligible modelled contribution of d>20 μ m particles to total mass, compared to 15 % in the observations. This work adds to the growing body of research that demonstrates the need for a process-based evaluation of climate model dust simulations to identify where improvements could be implemented. [ABSTRACT FROM AUTHOR]

Mineral dust aerosols are composed of a complex assemblage of various minerals depending on the region in which they originated. Given the different mineral composition of desert dust aerosols, different physicochemical properties and therefore varying climate effects are expected. Despite the known regional variations in mineral composition, chemical transport models typically assume that mineral dust aerosols have uniform composition. This study adds, for the first time, mineralogical information to the mineral dust emission scheme used in the chemical transport model COSMO–MUSCAT. We provide a detailed description of the implementation of the mineralogical database, GMINER (), together with a specific set of physical parameterizations in the model's mineral dust emission module, which led to a general improvement of the model performance when comparing the simulated mineral dust aerosols with measurements over the Sahara region for January–February 2022. The simulated mineral dust aerosol vertical distribution is tested by a comparison with aerosol lidar measurements from the lidar system PollyXT , located at Cape Verde. For a lofted mineral dust aerosol layer on 2 February at 05:00 UTC the lidar retrievals yield a dust mass concentration peak of 156 µgm-3 , while the model calculates the mineral dust peak at 136 µgm-3. The results highlight the possibility of using the model with resolved mineral dust composition for interpretation of the lidar measurements since a higher absorption in the UV–Vis wavelengths is correlated with particles having a higher hematite content. Additionally, the comparison with in situ mineralogical measurements of dust aerosol particles shows that more of them are needed for model evaluation. [ABSTRACT FROM AUTHOR]

Greenland ice core records exhibited 100-fold higher dust concentrations during the Last Glacial Maximum (LGM) than during the Holocene, and dust input temporal variability corresponded to different climate states in the LGM. While East Asian deserts, the Sahara, and European loess have been suggested as the potential source areas (PSAs) for Greenland LGM dust, millennial-scale variability in their relative contributions within the LGM remains poorly constrained. Here, we present the morphological, mineralogical, and geochemical characteristics of insoluble microparticles to constrain the provenance of dust in Greenland NEEM ice core samples covering cold Greenland Stadials (GS)-2.1a to GS-3 (~ 14.7 to 27.1 kyr ago) in the LGM. The analysis was conducted on individual particles in microdroplet samples by scanning electron microscopy with energy dispersive X-ray spectroscopy and Raman microspectroscopy. We found that the kaolinite-to-chlorite (K/C) ratios and chemical index of alteration (CIA) values were substantially higher (K/C: 1.4 ± 0.7, CIA: 74.7 ± 2.9) during GS-2.1a to 2.1c than during GS-3 (K/C: 0.5 ± 0.1, CIA: 65.8 ± 2.8). Our records revealed a significant increase in Saharan dust contributions from GS-2.1a to GS-2.1c and that the Gobi Desert and/or European loess were potential source(s) during GS-3. This conclusion is further supported by distinctly different carbon contents in particles corresponding to GS-2.1 and GS-3. These results are consistent with previous estimates of proportional dust source contributions obtained using a mixing model based on Pb and Sr isotopic compositions in NEEM LGM ice and indicate millennial-scale changes in Greenland dust provenance that are probably linked to large-scale atmospheric circulation variabilities during the LGM. [ABSTRACT FROM AUTHOR]

In June 2020, a record-breaking Saharan dust storm, known as the "Godzilla" extreme event, caused significant dust transport from the Sahara Desert across the Atlantic Ocean to the United States. Based on satellite observations, the magnitude of aerosol optical depth (AOD) has consistently remained highest over the Atlantic Ocean for the past 18 years. This study uses satellite observations (including MODIS and CALIOP) and MERRA-2 reanalysis products to investigate the relationships between dust and marine clouds. During this extreme event, the concentration of AOD exhibits a synchronous anomaly with the cloud fraction (CF). Principal components analysis (PCA) results show that the enhanced temperature and specific humidity near the surface contribute the most to cloud development over the tropical Atlantic Ocean. Despite the reduced sensitivity of CF to aerosols, the semi-direct effect of dust can still play a crucial role during this extreme dust storm. We found that the presence of absorbing aerosols above the cloud layers warms the air, accompanied by an enhancement of surface moisture, thereby benefiting low-level cloud coverage. [ABSTRACT FROM AUTHOR]

African desert dust is emitted and long-range transported with multiple effects on climate, air quality, cryosphere, and ecosystems. On 21–23 February 2021, dust from a sand and dust storm in northern Africa was transported to Finland, north of 60°N. The episode was predicted 5 days in advance by the global operational SILAM forecast, and its key features were confirmed and detailed by a retrospective analysis. The scavenging of dust by snowfall and freezing rain in Finland resulted in a rare case of substantial mineral dust contamination of snow surfaces over a large area in the southern part of the country. A citizen science campaign was set up to collect contaminated snow samples prepared according to the scientists' instructions. The campaign gained wide national interest in television, radio, newspapers and social media, and dust samples were received from 525 locations in Finland, up to 64.3°N. The samples were utilised in investigating the ability of an atmospheric dispersion model to simulate the dust episode. The analysis confirmed that dust came from a wide Sahara and Sahel area from 5000 km away. Our results reveal the features of this rare event and demonstrate how deposition samples can be used to evaluate the skills and limitations of current atmospheric models in simulating transport of African dust towards northern Europe. [ABSTRACT FROM AUTHOR]

This interdisciplinary dialogue draws on climatology and cultural studies to explore the phenomenon of "Saharan dust" that passes through and beyond the Spanish Mediterranean Basin. The dialogic process seeks to unearth the power relations within which weather stories and the authors are always already entangled, with a view to re-imagining weather writing and climatic storytelling in decolonial terms. Our parallel inquiries trace how origin stories, material mobilities, atmospheres, and environmental regulation work to codify the aeolian dust as an intrusion across borders. Drawing on critical theory, we argue that this weather "from" the Sahara Desert is othered in Eurocentric weather narratives, mapping onto geopolitical logic of "Fortress Europe". Our research is instructed by postcolonial thought, political ecology, and the speculative feminist position of weathering. Through critical engagement with science in context, we dwell lastly on African air quality and experiences of weathering atmospheric dust further upwind. Our concluding comments speculatively drift with Mediterranean winds to animate a positionality of middleness. [ABSTRACT FROM AUTHOR]

This paper presents a study of a strong desert dust episode over the Iberian Peninsula, and its effect on the spectral ultraviolet (UV) irradiance in Granada, Spain. Remote sensing measurements, forecast models, and synoptic analysis are used to identify a Saharan desert dust outbreak that affected the Iberian Peninsula starting 20 July 2009. Additionally, a Bentham DMc150 spectroradiometer is employed to obtain global, direct and diffuse spectral UV irradiances every 15 minutes in Granada. The desert dust caused a large attenuation of the direct UV irradiance (up to 55%), while the diffuse UV irradiance increased up to 40% at 400 nm. The UVSPEC/LibRadtran radiative transfer model is used to study the spectral dependence of the experimental UV irradiance ratios (ratios of spectral irradiance for the day with the highest aerosol load to that measured in days with low-moderate load). The spectral increase or decrease of the UV direct irradiance ratios depends on a new parameter: a threshold wavelength. The spectral dependence of the UV diffuse irradiance ratio can be explained because under the influence of the intense dust outbreak, the Mie scattering by aerosols at shorter wavelengths is stronger than the Rayleigh scattering by gases. Finally, the sensitivity analysis of the aerosol absorption properties shows a substantial attenuation of UV spectral irradiance with a weak spectral dependence. [ABSTRACT FROM AUTHOR]

In the framework of the Saharan Mineral Dust Experiment (SAMUM) for the first time the spectral dependence of particle linear depolarization ratios was measured by combining four lidar systems. In this paper these measurements are compared with results from scattering theory based on the T-matrix method. For this purpose, in situ measurements—size distribution, shape distribution and refractive index—were used as input parameters; particle shape was approximated by spheroids. A sensitivity study showed that lidar-related parameters—lidar ratio and linear depolarization ratio —are very sensitive to changes of all parameters. The simulated values of the are in the range of 20% and 31% and thus in the range of the measurements. The spectral dependence is weak, so that it could not be resolved by the measurements. Calculated lidar ratios based on the measured microphysics and considering equivalent radii up to 7.5 μm show a range of possible values between 29 and 50 sr at . Larger might be possible if the real part of the refractive index is small and the imaginary part is large. A strict validation was however not possible as too many microphysical parameters influence and that could not be measured with the required accuracy. [ABSTRACT FROM AUTHOR]

In May/June 2006, the largest mineral dust experiment to date (Saharan Mineral Dust Experiment, SAMUM-1) was conducted in Southern Morocco. The aim was to characterize dust particles near the world's largest mineral dust source, and to quantify dust-related radiative effects. At one of the two ground-based measurement sites dust particle size distribution, optical, hygroscopic, chemical and structural particle characteristics were measured. One research aircraft mainly measured solar spectral irradiances and surface albedo. The other aircraft provided in situ physical aerosol measurements and samples and lidar profiles through the dust layers. Three ground-based lidars were operated at the second ground-based measurement site. They determined optical dust properties, particle shape and temporal development of dust layers. Columnar, ground-based sun photometer measurements complemented the lidar data. Additionally a station in Évora, Portugal monitored dust outbreaks from the North African source region to the Iberian Peninsula during SAMUM-1. Volumetric and columnar closure exercises utilized these detailed measurements of dust characteristics together with optical and radiative transfer models. Concurrent developments of a mesoscale dust transport model were validated with the experimental data. The paper gives an overview over rationale and design of SAMUM-1, introduces and highlights the subsequent reports on experimental and modelling results. [ABSTRACT FROM AUTHOR]

ABSTRACT This study focuses on the atmospheric temperature response to dust deduced from a new source of data–the European Reanalysis (ERA) increments. These increments are the systematic errors of global climate models, generated in the reanalysis procedure. The model errors result not only from the lack of desert dust but also from a complex combination of many kinds of model errors. Over the Sahara desert the lack of dust radiative effect is believed to be a predominant model defect which should significantly affect the increments. This dust effect was examined by considering correlation between the increments and remotely sensed dust. Comparisons were made between April temporal variations of the ERA analysis increments and the variations of the Total Ozone Mapping Spectrometer aerosol index (AI) between 1979 and 1993. The distinctive structure was identified in the distribution of correlation composed of three nested areas with high positive correlation (>0.5), low correlation and high negative correlation (< -0.5). The innermost positive correlation area (PCA) is a large area near the center of the Sahara desert. For some local maxima inside this area the correlation even exceeds 0.8. The outermost negative correlation area (NCA) is not uniform. It consists of some areas over the eastern and western parts of North Africa with a relatively small amount of dust. Inside those areas both positive and negative high correlations exist at pressure levels ranging from 850 to 700 hPa, with the peak values near 775 hPa. Dust-forced heating (cooling) inside the PCA (NCA) is accompanied by changes in the static instability of the atmosphere above the dust layer. The reanalysis data of the European Center for Medium Range Weather Forecast (ECMWF) suggest that the PCA (NCA) corresponds mainly to anticyclonic (cyclonic) flow, negative (positive) vorticity and downward (upward) airflow. These findings are associated with the interaction between dust-forced heating/cooling and atmospheric circulation. This paper contributes to a better understanding of dust radiative processes missed in the model. [ABSTRACT FROM AUTHOR]

The Sahara is the world’s largest source of aeolian desert dust, but precise information on specific sources of this material is poor and sometimes contradictory. This paper uses daily data from the Total Ozone Mapping Spectrometer (TOMS) for 1999 to identify source areas for major dust events and their trajectories of long-range transport. Two major source areas are identified: the Bodélé depression and an area covering eastern Mauritania, western Mali and southern Algeria. Both of these major dust sources are primarily driven by natural factors since they are little affected by anthropogenic activities. [ABSTRACT FROM AUTHOR]

Mineral dust aerosols are composed from a complex assemblage of various minerals depending on the region they originated. Giving the different mineral composition of desert dust aerosols, different physico-chemical properties and therefore varying climate effects are expected. Despite the known regional variations in mineral composition, chemical transport models typically assume that mineral dust aerosol have uniform composition. This study adds, for the first time, mineralogical information to the mineral dust emission scheme used in the chemical transport model COSMO-MUSCAT. We provide a detailed description of the implementation of the mineralogical database, GMINER (Nickovic et al., 2012), together with a specific set of physical parametrizations in the model's mineral dust emission module. These changes lead to a general improvement of the model performance when comparing the simulated mineral dust aerosols with measurements over the Sahara Desert region for January–February 2022. The simulated mineral dust aerosol vertical distribution is tested by a comparison with aerosol lidar measurements from the lidar system PollyXT, located at Cape Verde. For a lofted mineral dust aerosol layer on the 2 February 5:00 UTC the lidar retrievals yield on a dust mass concentration peak of 156 μg/m3 while the model calculates the mineral dust peak at 136 μg/m3. The results highlight the possibility of using the model with resolved mineral dust composition for interpretation of the lidar measurements since higher absorption the UV-VIS wavelength is correlated to particles having higher hematite content. Additionally, the comparison with in-situ mineralogical measurements of dust aerosol particles show how important they are, but also that more of them are needed for model evaluation. [ABSTRACT FROM AUTHOR]

This paper aims to study a new solar panels cleaning device based on the ionic wind produced by corona discharge plasma. The device comprises a high-voltage electrode composed of a series of parallel sharp needles and a grounded frame electrode. The system is moved using two driven wheels fixed at its extremities, and is placed at a few millimetres above the solar panel surface at. The cleaning operation is done by moving the dust particles from the surface using the ionic wind coming out through a 5 mm-width opening located at the bottom of the device. The study was carried out by measuring the wind velocity and the cleaning efficiency as a function of the device movement speed and the applied voltage level. The results obtained using Algerian Sahara sand dust allowed to obtain an ionic wind velocity of about 2 m/s and a cleaning efficiency that reaches 95% with a consumed power of about 20 W. • A new cleaning device of solar panels was developed and investigated. • The technique is based on the ionic wind produced by corona discharge plasma. • The device is provided with two driven wheels moving along the panel. • The ionic wind is capable of removing 95% of the sand particles in one passage. • The power consumed is about twenty watts. [ABSTRACT FROM AUTHOR]

During the dry season, dust particles on photovoltaic modules (PV modules) are a regular occurrence in Calabar, Cross River State. This dusty condition or environment is caused by the migration of dust particles from the Sahara region via the east-west wind. The concentration of dust on PV modules has an impact on the overall performance of solar energy systems. This research looks into the effect of dust particles on the output power of solar modules. This investigation was carried out by subjecting 80-watt monocrystalline PV modules to an outdoor experiment and analyzing the changes in current and voltage from the control and dusty PV modules with a digital multimeter. Other environmental factors such as relative humidity, ambient temperature, and solar radiation were also measured with a hygrometer, thermometer, and solar power meter respectively. Appropriate formulars were employed to calculate output power and efficiency. Dust particles on the surface of PV modules dramatically reduces the quantity of sunlight that penetrate the panel by 21.10%, resulting in a drop in the system's overall output power. The study emphasizes on the importance of frequent cleaning and maintenance of PV systems. [ABSTRACT FROM AUTHOR]

The particle size distribution (PSD) of mineral dust has a strong effect on the impacts of dust on climate. However, our understanding of the emitted dust PSD, including its variability and the fraction of super-coarse dust (diameter >10 µm), remains limited. Here, we provide new insights into the size-resolved dust emission process based on a field campaign performed in the Moroccan Sahara in September 2019 in the context of the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) project. The obtained dust concentration and diffusive flux PSDs show significant dependencies upon the friction velocity (u*), wind direction and type of event (regular events versus haboob events). For instance, the number fraction of sub-micrometre particles increases with u* , along with a large decrease in the mass fraction of super-coarse dust. We identify dry deposition, which is modulated by u* and fetch length, as a potential cause for this PSD variability. Using a resistance model constrained with field observations to estimate the dry deposition flux and thereby also the emitted dust flux, we show that deposition could represent up to ∼90% of the emission of super-coarse particles (>10 µm) and up to ∼65% of the emission of particles as small as ∼5 µm in diameter. Importantly, removing the deposition component significantly reduces the variability with u* in the PSD of the emitted dust flux compared with the diffusive flux, particularly for super-coarse dust. The differences between regular and haboob event concentration and diffusive flux PSDs are suspected to result from a smaller and variable dust source fetch during the haboob events, and/or an increased resistance of soil aggregates to fragmentation associated with the observed increase in relative humidity along the haboob outflow. Finally, compared to the invariant emitted dust flux PSD estimated based on brittle fragmentation theory, we obtain a substantially higher proportion of super-micrometre particles in the dust flux. Overall, our results suggest that dry deposition needs to be adequately considered to estimate the emitted PSD, even in studies limited to the fine and coarse size ranges (<10 µm). [ABSTRACT FROM AUTHOR]

Aerosol reanalysis datasets are model-based, observationally constrained, continuous 3D aerosol fields with a relatively high temporal frequency that can be used to assess aerosol variations and trends, climate effects, and impacts on socioeconomic sectors, such as health. Here we compare and assess the recently published MONARCH (Multiscale Online Non-hydrostatic AtmospheRe CHemistry) high-resolution regional desert dust reanalysis over northern Africa, the Middle East, and Europe (NAMEE) with a combination of ground-based observations and space-based dust retrievals and products. In particular, we compare the total and coarse dust optical depth (DOD) from the new reanalysis with DOD products derived from MODIS (MODerate resolution Imaging Spectroradiometer), MISR (Multi-angle Imaging SpectroRadiometer), and IASI (Infrared Atmospheric Sounding Interferometer) spaceborne instruments. Despite the larger uncertainties, satellite-based datasets provide a better geographical coverage than ground-based observations, and the use of different retrievals and products allows at least partially overcoming some single-product weaknesses in the comparison. Nevertheless, limitations and uncertainties due to the type of sensor, its operating principle, its sensitivity, its temporal and spatial resolution, and the methodology for retrieving or further deriving dust products are factors that bias the reanalysis assessment. We, therefore, also use ground-based DOD observations provided by 238 stations of the AERONET (AErosol RObotic NETwork) located within the NAMEE region as a reference evaluation dataset. In particular, prior to the reanalysis assessment, the satellite datasets were evaluated against AERONET, showing moderate underestimations in the vicinities of dust sources and downwind regions, whereas small or significant overestimations, depending on the dataset, can be found in the remote regions. Taking these results into consideration, the MONARCH reanalysis assessment shows that total and coarse-DOD simulations are consistent with satellite- and ground-based data, qualitatively capturing the major dust sources in the area in addition to the dust transport patterns. Moreover, the MONARCH reanalysis reproduces the seasonal dust cycle, identifying the increased dust activity that occurred in the NAMEE region during spring and summer. The quantitative comparison between the MONARCH reanalysis DOD and satellite multi-sensor products shows that the reanalysis tends to slightly overestimate the desert dust that is emitted from the source regions and underestimate the transported dust over the outflow regions, implying that the model's removal of dust particles from the atmosphere, through deposition processes, is too effective. More specifically, small positive biases are found over the Sahara desert (0.04) and negative biases over the Atlantic Ocean and the Arabian Sea (- 0.04), which constitute the main pathways of the long-range dust transport. Considering the DOD values recorded on average there, such discrepancies can be considered low, as the low relative bias in the Sahara desert (< 50 %) and over the adjacent maritime regions (< 100 %) certifies. Similarly, over areas with intense dust activity, the linear correlation coefficient between the MONARCH reanalysis simulations and the ensemble of the satellite products is significantly high for both total and coarse DOD, reaching 0.8 over the Middle East, the Atlantic Ocean, and the Arabian Sea and exceeding it over the African continent. Moreover, the low relative biases and high correlations are associated with regions for which large numbers of observations are available, thus allowing for robust reanalysis assessment. [ABSTRACT FROM AUTHOR]

Desert dust accounts for a substantial fraction of the total atmospheric aerosol loading. It produces important impacts on the Earth system due to its nutrient content and interactions with radiation and clouds. However, current climate models greatly underestimate its airborne lifetime and transport. For instance, super coarse Saharan dust particles (with diameters greater than 10 µm) have repeatedly been detected in the Americas, but models fail to reproduce their transatlantic transport. In this study, we investigated the extent to which vertical turbulent mixing in the Saharan Air Layer (SAL) is capable of delaying particle deposition. We developed a theory based on the solution to a one‐dimensional dust mass balance and validated our results using large‐eddy simulation (LES) of a turbulent shear layer. We found that eddy motion can increase the lifetime of suspended particles by up to a factor of 2 when compared with laminar flows. Moreover, we found that the increase in a lifetime can be reliably estimated solely as a function of the particle Peclet number (the ratio of the mixing timescale to the settling timescale). By considering both the effects of turbulent mixing and dust asphericity, we explained to a large extent the presence of super coarse Saharan dust in the Caribbean observed during the Saharan Aerosol Long‐Range Transport and Aerosol‐Cloud‐Interaction Experiment (SALTRACE) field campaign. The theory for the lifetime of coarse particles in turbulent flows developed in this study is also expected to be applicable in other similar geophysical problems, such as phytoplankton sinking in the ocean mixed layer. Plain Language Summary: Dust emitted from desert surfaces on Earth impacts climate and weather by affecting cloud formation and interacting with solar and terrestrial radiation. It also carries important nutrients that feed land and ocean ecosystems. Therefore, it is important to accurately predict for how long these particles remain suspended in the atmosphere. However, current models underestimate this time and the associated horizontal transport. For example, it is still not well understood how super coarse dust particles (which deposit faster than smaller particles) are able to move from the Sahara desert to the Americas. Our study tested the hypothesis that vertical mixing caused by turbulence in the upper atmosphere (above about 2 km from the ground) is one of the mechanisms responsible for that phenomenon. Using the principle of mass conservation, as well as computer simulations, we found that turbulence can even double the period of time that dust remains suspended in the atmosphere. When also factoring in the irregular shape of dust particles, which decreases their deposition speeds, our theory was able to explain to a great extent observations of super coarse Saharan particles in the Caribbean. This suggests that turbulence is a key mechanism by which dust gets transported over long distances. Key Points: Turbulent mixing is capable of at most doubling the atmospheric lifetime of coarse aerosols in elevated layersAirborne lifetime of particles depends only on the relative strength of gravitational settling and turbulent mixingDust asphericity and free tropospheric mixing help explain the transport of super coarse Saharan dust to the Caribbean [ABSTRACT FROM AUTHOR]

The chemical and morphological properties of mineral dust aerosols emitted by wind erosion from arid and semi-arid regions influence climate, ocean, and land ecosystems; air quality; and multiple socio-economic sectors. However, there is an incomplete understanding of the emitted dust particle size distribution (PSD) in terms of its constituent minerals that typically result from the fragmentation of soil aggregates during wind erosion. The emitted dust PSD affects the duration of particle transport and thus each mineral's global distribution, along with its specific effect upon climate. This lack of understanding is largely due to the scarcity of relevant in situ measurements in dust sources. To advance our understanding of the physicochemical properties of the emitted dust PSD, we present insights into the elemental composition and morphology of individual dust particles collected during the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) field campaign in the Moroccan Sahara in September 2019. We analyzed more than 300 000 freshly emitted individual particles by performing offline analysis in the laboratory using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDX). Eight major particle-type classes were identified with clay minerals making up the majority of the analyzed particles both by number and mass, followed by quartz, whereas carbonates and feldspar contributed to a lesser extent. We provide an exhaustive analysis of the PSD and potential mixing state of different particle types, focusing largely on iron-rich (Fe oxide-hydroxides) and feldspar particles, which are key to the effects of dust upon radiation and clouds, respectively. Nearly pure or externally mixed Fe oxide-hydroxides are present mostly in diameters smaller than 2 µm , with the highest fraction below 1 µm at about 3.75 % abundance by mass. Fe oxide-hydroxides tend to be increasingly internally mixed with other minerals, especially clays, as particle size increases; i.e., the volume fraction of Fe oxide-hydroxides in aggregates decreases with particle size. Pure (externally mixed) feldspar represented 3.2 % of all the particles by mass, of which we estimated about a 10th to be K-feldspar. The externally mixed total feldspar and K-feldspar abundances are relatively invariant with particle size, in contrast to the increasing abundance of feldspar-like (internally mixed) aggregates with particle size with mass fractions ranging from 5 % to 18 %. We also found that overall the median aspect ratio is rather constant across particle size and mineral groups, although we obtain slightly higher aspect ratios for internally mixed particles. The detailed information on the composition of freshly emitted individual dust particles and quantitative analysis of their mixing state presented here can be used to constrain climate models including mineral species in their representation of the dust cycle. [ABSTRACT FROM AUTHOR]

The vertical aerosol layering of the troposphere is poorly documented in mountainous regions, particularly in the Alpine valleys, which are influenced by valley and mountain winds. To improve our knowledge of particulate matter trapped in the Annecy valley, synergetic measurements performed by a ground-based meteorological Raman lidar and a Rayleigh-Mie lidar aboard an ultralight aircraft were implemented as part of the Lacustrine-Water vApor Isotope inVentory Experiment (L-WAIVE) over Lake Annecy. These observations were complemented by satellite observations and Lagrangian modeling. The vertical profiles of aerosol optical properties (e.g., aerosol extinction coefficient (AEC), lidar ratio (LR), particle linear depolarization ratio (PDR)) are derived from lidar measurements at 355 nm during the period between 13 and 22 June 2019. The background aerosol content with an aerosol optical thickness (AOT) of 0.10 ± 0.05, corresponding to local–regional conditions influenced by anthropogenic pollution, has been characterized over the entirety of Lake Annecy thanks to the mobile ultralight payload. The aerosol optical properties are shown to be particularly variable over time in the atmospheric column, with mean LRs (PDRs) varying between 40 ± 8 and 115 ± 15 sr (2 ± 1 and 35 ± 2%). Those conditions can be disturbed by air masses that have recirculated over the valley, as well as by contributions from neighboring valleys. We have observed an important disruption in the atmospheric aerosol profiles by the arrival of an exceptionally dry air mass (RH ~ 30%), containing aerosols identified as coming from the Great Western Erg (AOT ~ 0.5, LR = 65 ± 10 sr, PDR = 20–35%) in the Sahara. These desert dust particles are shown to influence the entire atmospheric column in the Annecy valley. Such an experimental approach, coupling upward and downward lidar and spaceborne observation/Lagrangian modelling, was shown to be of significant interest for the long-term monitoring of the evolution of aerosol loads over deep valleys. It allows a better understanding of the influence of dust storms in the presence of severe convective weather processes. [ABSTRACT FROM AUTHOR]

Recent research has convincingly shown the advantages of combining environmental magnetism and geochemical analyses for the proxy estimation of anthropogenic pollution due to their atmospheric deposition in local environments. Few studies have also focused on anthropogenic particles deposited on snow. However, papers reporting on Sahara dust particles deposited on snow in central Europe and which involve magnetic methods are missing. To the best of our knowledge, this is the first study investigating the magnetic features of the SDE recorded in snowfall in this part of Europe (i.e. Poland). Our aim was to provide the magnetic characteristics and chemical elemental compositions of a snow horizon containing Saharan dust deposited near the Polish Jakuszyce meteorological station during a snowfall event that occurred from the 1st to the February 7, 2021. Samples of snow with and without Saharan dust were analysed with respect to iron oxide contents (magnetic susceptibility, hysteresis loop, magnetic remanence acquisition) and compared with chemical compositions. Our results revealed the presence of both ferrimagnetic magnetite and antiferromagnetic hematite in the dust-enriched horizon, and the diamagnetic behaviour of the reference layer consisting of 'pure' snow. The samples recorded the presence of geogenic elements such as Al, Fe, Mn, and Ti, anthropogenic elements such as As, Co, Cr, Cu, Ni, Pb, and Zn, and nutrients including Ca and K. The total concentrations of geogenic elements, nutrients, and anthropogenic elements in the snow samples with deposited Saharan dust were, respectively, >3700, >320, and >110 times greater than in the samples without Saharan dust. These findings may serve as reference data for a variety of environmental magnetic studies. [Display omitted] [ABSTRACT FROM AUTHOR]

During abrupt climate changes of the last glacial period paleorecords show large amplitude changes in the dust cycle. We use Earth System model simulations to evaluate processes operating across these events. Idealized Heinrich stadial‐like simulations show a southwards migration of tropical rainfall that dries the Sahel and reduces wet deposition causing a widespread enhancement of tropical dust loading. However, several discrepancies with marine core dust deposition reconstructions are evident. Simulations with a more limited freshwater forcing (0.4 Sv instead of 1.0 Sv) and weaker cooling over the North Atlantic (less than 3°C) show a switch in sign of the stadial dust deposition anomaly in several regions, improving agreement with paleorecords. The simulated dust cycle therefore displays in places a non‐linear response to abrupt change. The global‐mean stadial dust radiative forcing in the more realistic simulations is around −0.2 to −0.6 W m−2 and so could represent an amplifying feedback during these events. Plain Language Summary: Mineral dust in the atmosphere is mostly sourced from arid regions like the Sahara desert. The amount and geographical spread of this dust in the atmosphere is sensitive to environmental conditions such as drought. Paleoclimate records show that rapid cooling events centered on the North Atlantic during the last ice‐age also saw large increases in the rate of dust deposited over the ocean. Earth System models are a computational tool that can be used to understand the links between climate and the dust cycle. Using a series of such simulations we found that abrupt cooling events in the North Atlantic can lead to a massive increase in dust over the equatorial (tropical) regions. However, the model's response is in many places non‐linear, meaning that the change in dust is very sensitive to the magnitude of the climate changes occurring. This non‐linearity is mostly due to interactions between changes in the water cycle and the dust. We show that a less severe cooling produces a more realistic dust response when evaluated against paleo‐dust records. Since dust scatters incoming sunlight, increased atmospheric dust during these events may have amplified and even extended the cold phases. Key Points: Freshwater hosing forcing increases tropical dust loading in Earth System model simulations of the last glacial maximumSimulated response is non‐linear with forcing in some regions, particularly North AfricaWeaker events improve agreement with data and emitted dust produces a self‐amplifying feedback [ABSTRACT FROM AUTHOR]

Mineral dust and sea spray aerosol represent important sources of ice-nucleating particles (INPs), the minor fraction of aerosol particles able to trigger cloud ice crystal formation and, consequently, influence multiple climate-relevant cloud properties including lifetime, radiative properties and precipitation initiation efficiency. Mineral dust is considered the dominant INP source in many parts of the world due to its ice nucleation efficiency and its sheer abundance, with global emission rates of up to 4700 Tg a -1. However, INPs emitted from the ocean surface in sea spray aerosol frequently dominate INP populations in remote marine environments, including parts of the Southern Ocean where cloud-resolving model simulations have demonstrated that cloud radiative properties are likely strongly controlled by INPs. Here we report INP concentrations measured in aerosol and seawater samples during Air Quality and Climate Change in the Arabian Basin (AQABA), a shipborne campaign that spanned the Red Sea, Gulf of Aden, Arabian Sea, Arabian Gulf and part of the Mediterranean. In aerosol samples collected within a few hundred kilometers of the first and second ranked sources of dust globally, the Sahara and Arabian Peninsula, INP concentrations ranged from 0.2 to 11 L -1 at - 20 ∘ C with observed ice-active surface site densities (ns) 1–3 orders of magnitude below levels predicted by mineral dust INP parameterizations. Over half of the samples (at least 14 of 26) were collected during dust storms with average dust mass concentrations between 150 and 490 µ g m -3 (PM 10), as simulated by the Modern-Era Retrospective analysis for Research and Application, version 2 (MERRA-2). The impacts of heat and peroxide treatments indicate that organics dominated the observed ice nucleation (IN) activity at temperatures ≥ - 15 ∘ C with proteinaceous (heat-labile) INPs frequently observed at high freezing temperatures >-10 ∘ C. INP concentrations in seawater samples ranged between 3 and 46 mL -1 at - 19 ∘ C, demonstrating the relatively low INP source potential of seawater in the region as compared to seawater from multiple other regions reported previously. Overall, our results demonstrate that despite proximity to the Sahara and the Arabian Peninsula and the dominance of mineral dust in the aerosol sampled, existing mineral dust parameterizations alone would not skillfully represent the near-surface ns in the observed temperature regime (- 6 to - 25 ∘ C). Future efforts to develop or improve representations of dust INPs at modest supercooling (≥-15 ∘ C) would benefit from a characterization of the specific organic species associated with dust INPs. More generally, an improved understanding of the organic species associated with increased IN activity and their variability across dust source regions would directly inform efforts to determine whether ns -based parameterizations are appropriate for faithful representation of dust INPs in this sensitive temperature regime, whether region-specific parameterizations are required, or whether an alternative to the ns approach is necessary. [ABSTRACT FROM AUTHOR]

The shortwave direct radiative effect of dust, the difference between net shortwave radiative flux in a cloud free and cloud and aerosol free atmosphere, is typically estimated using forward calculations made with a radiative transfer model. However, estimates of the direct radiative effect made via this initial method can be highly uncertain due to difficultly in accurately describing the relevant optical and physical properties of dust used in these calculations. An alternative approach to estimate this effect is to determine the forcing efficiency, or the direct radiative effect normalized by aerosol optical depth. While this approach avoids the uncertainties associated with the initial method for calculating the direct effect, random errors and biases associated with this approach have not been thoroughly examined in literature. Here we explore biases in this observation‐based approach that are related to atmospheric water vapor. We use observations to show that over the Sahara Desert dust optical depth and column‐integrated atmospheric water vapor are positively correlated. We use three idealized radiative models of varying complexity to demonstrate that a positive correlation between dust and water vapor produces a positive bias in the dust forcing efficiency estimated via the observation‐based method. We describe a simple modification to the observation‐based method that correctly accounts for the correlation between dust and water vapor when estimating the forcing efficiency and use this method to estimate the instantaneous forcing efficiency of dust over the Sahara Desert using satellite data, obtaining −12.3 ± 6.68 to 20.9 ± 11.9 W m−2 per unit optical depth. Plain Language Summary: The presence of suspended dust in the Earth's atmosphere affects the planetary energy budget via the direct radiative effect, and researchers typically use radiative transfer models to quantify the magnitude of this effect. However calculations of the direct radiative effect made in this manner are highly uncertain due to a lack of precise knowledge of a number of relevant dust properties. An observation‐based approach that circumvents these challenges exists, yet uncertainties associated with this method have not been extensively investigated. Here we identify one physical mechanism that produces a bias when estimating the dust direct effect via the observational approach, which is the observed correlation between atmospheric water vapor and dust. We describe a simple solution to account for this effect in direct effect calculations and then use this corrected method along with data from satellites to estimate the dust direct effect over North Africa, finding a smaller value than what had been reported by earlier studies. Key Points: Biases in dust shortwave forcing efficiency estimated via observational methods arise due to solar aborption of water vaporAn observational method is described that accounts for potential biases in the dust shortwave forcing efficiencyWhen applied to data over North Africa we estimate the dust shortwave forcing efficiency to lie within in –12.3 to –20.9 W m−2 per unit optical depth [ABSTRACT FROM AUTHOR]

Atlantic hurricane activity experienced a pronounced lull during the 1970s and 1980s. The current explanation that anthropogenic aerosol radiative forcing cooled the sea surface locally fails to capture the magnitude of this large decrease in activity. To explain this hurricane drought, we propose that the radiative effects of sulfate aerosols from Europe and North-America decreased precipitation in the Sahara-Sahel region, leading to an enhancement of dust regional emissions and transport over the Atlantic. This dust in turn enhanced the local decrease of sea-surface temperature and of hurricane activity. Here, we show that dust emissions from the Sahara peaked in phase with regional sulfate aerosol optical thickness and Sahel drought conditions, and that dust optical depth variations alone can explain nearly half of the sea-surface temperature depression in the 1970s and 1980s. Atlantic hurricane numbers noticeably decreased in the 1970s and 1980s partly due to the cooling effect of eolian dust lofted from the Sahara, in response to local climate effects of aerosol pollutants emitted from Europe and North America. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of a strong Saharan dust event on longwave (LW) irradiance recorded at Granada (Southeastern Spain) on 6 September 2007. A detailed comparison with shortwave (SW) radiative effects for the same dust event is also shown. For these goals, simultaneous measurements of LW and SW irradiance were used together with the aerosol optical depth at 675 nm (AOD 675 ) derived from a Cimel CE-318 sun-photometer. LW irradiance on 6 September (AOD 675 ranged between 0.8 and 1.5) increased 8.4% on average compared to a no-dust day (4 September, AOD 675 below 0.15), while the SW irradiance was notably reduced about 28.2%. The study also showed that an increase of one unit in the AOD 675 led to an increase (decrease) of LW (SW) irradiance of 20 (187) W/m 2 . Hence, the LW contribution to offset partially the large SW decrease at surface strongly depends on the aerosol load, changing from 40% for AOD 675 ~ 0.8 to 20% for AOD 675 ~ 1.5. On daily average, LW radiative effect was about 39% of the SW one and, therefore, the intense decrease of SW irradiance due to dust particles was substantially offset by the increase of the LW irradiance. [ABSTRACT FROM AUTHOR]

African mineral dust is transported many thousands of kilometres from its source regions, and, because of its ability to nucleate ice, it plays a major role in cloud glaciation around the globe. The ice-nucleating activity of desert dust is influenced by its mineralogy, which varies substantially between source regions and across particle sizes. However, in models it is often assumed that the activity (expressed as active sites per unit surface area as a function of temperature) of atmospheric mineral dust is the same everywhere on the globe. Here, we find that the ice-nucleating activity of African desert dust sampled in the summertime marine boundary layer of Barbados (July and August 2017) is substantially lower than parameterizations based on soil from specific locations in the Sahara or dust sedimented from dust storms. We conclude that the activity of dust in Barbados' boundary layer is primarily defined by the low K-feldspar content of the dust, which is around 1 %. We propose that the dust we sampled in the Caribbean was from a region in western Africa (in and around the Sahel in Mauritania and Mali), which has a much lower feldspar content than other African sources across the Sahara and Sahel. [ABSTRACT FROM AUTHOR]

We quantified the combined effects of mineral dust nonsphericity and size on snow albedo reduction using the MOPSMAP (Modeled optical properties of ensembles of aerosol particles) package and SAMDS (Spectral Albedo Model for Dirty Snow) with the consideration of dust from Sahara, Greenland, San Juan Mountains, and Tibetan Plateau. Results indicate that the dust‐induced albedo reduction decreases by up to 30% as the effective radii of dust particles increase in 1–5 μm. Nonspherical dust enhances snow albedo reduction relative to spherical dust by up to 20%. Stronger enhancements are obtained for higher dust concentration and larger dust size. Furthermore, the dust nonsphericity‐induced enhancement of snow albedo reduction is more pronounced for more‐absorptive dust. Finally, we develop a new parameterization for quantifying the dependence of snow albedo reduction on dust nonsphericity and size, and provide a convenient way for assessing the climate impacts of dust in snow. Plain Language Summary: Mineral dust particles are a major type of light‐absorbing aerosols in the atmosphere, with the absorptivity closely dependent on their shape and size. Previous studies have confirmed that dust particles deposited on snow surface varied largely in size and shape, and caused the reduction of snow albedo worldwide. In this study, we quantified the effects of dust size and nonsphericity on the induced snow albedo reduction. Results show that small and nonspherical dust particles induce large snow albedo reduction, in comparison with large and spherical dust particles. We further develop a parameterization for the dust size and nonsphericity effects for application in climate models. Key Points: Mineral dust‐induced snow albedo reductions rapidly decrease as dust size increasesNonspherical dust causes larger snow albedo reduction than spherical dust by up to 20%A new parameterization is developed to improve the estimate of snow albedo reduction with dust size and nonsphericity [ABSTRACT FROM AUTHOR]

This study presents δ26Mg values, Mg2+ concentrations, δ18O and δ2H values of monthly collected rain and snow samples between 2014 and 2017 from north‐west Germany. The δ26Mg values of snow are similar to those of rain. Unlike δ18O and δ2H, neither δ26Mgprecipitation values nor Mg2+ concentrations display a relationship with air temperature. In contrast, δ26Mgprecipitation values and Mg2+ concentrations are correlated with precipitation amount. As previously suggested by other studies but now based on a larger data set, it is proposed that the δ26Mg values and Mg2+ concentrations are affected by the mineralogical composition and amount of airborne dust. Consequently, a small number of random precipitation samples cannot represent the complex processes influencing the δ26Mgprecipitation values. δ26Mgprecipitation can be used to differentiate between seawater aerosols, carbonate and silicate dust. Silicate dust is typified by higher Mg concentrations and δ26Mg values compared to carbonate dust. Concerning carbonates, dolostone dust has higher Mg concentrations and δ26Mg values, while limestone dust is Mg‐lean with lower δ26Mg values. Dust of anthropogenic origin in the region can come from active limestone and dolostone quarries, surface mining of siliciclastics, and agriculture on silicate‐rich soils. Although dust of this mineralogy can also be of natural origin, most natural dust consists of airborne silicates transported by wind systems from the Sahara to Europe. Higher δ26Mgprecipitation values would indicate silicate or dolostone dust influx. Lower δ26Mgprecipitation values suggest lower dust concentrations and a predominantly calcitic dust mineralogy. It appears that δ26Mgprecipitation is most probably influenced by changes in weather conditions and natural and anthropogenic dust origin. This study implies that δ26Mgprecipitation is a potential proxy for dust mineralogy and fluxes. Nevertheless, further research should include the determination of atmospheric dust mineralogy and their fractions as well as air mass back trajectory analysis to identify the source(s) of dust. [ABSTRACT FROM AUTHOR]

India as a hotspot for air pollution has heavy black carbon (BC) and dust (DU) loadings. BC has been identified to significantly impact the Indian climate. However, whether BC-climate interactions regulate Indian DU during the premonsoon season is unclear. Here, using long-term Reanalysis data, we show that Indian DU is positively correlated to northern Indian BC while negatively correlated to southern Indian BC. We further identify the mechanism of BC-dust-climate interactions revealed during COVID-19. BC reduction in northern India due to lockdown decreases solar heating in the atmosphere and increases surface albedo of the Tibetan Plateau (TP), inducing a descending atmospheric motion. Colder air from the TP together with warmer southern Indian air heated by biomass burning BC results in easterly wind anomalies, which reduces dust transport from the Middle East and Sahara and local dust emissions. The premonsoon aerosol-climate interactions delay the outbreak of the subsequent Indian summer monsoon. Black carbon produced by human activities impacts climate. Here, the authors find that black carbon-climate interactions regulate Indian dust during the premonsoon season and further affect the outbreak of the subsequent Indian summer monsoon. [ABSTRACT FROM AUTHOR]

The total and individual aerosol direct radiative effects (ADREs) were estimated for clear-sky conditions using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations and radiative transfer model. In this study, a parametric sensitivity analysis was performed for the Santa Barbara DISORT Atmospheric Radiative Transfer model using a global sensitivity analysis method. Uncertainties in the ADREs due to aerosol optical properties and surface albedo errors were evaluated. The single-scattering albedo and asymmetry factor for marine, dust, pollution, and smoke aerosols required for the model calculations were obtained from the classified AErosol RObotic NETwork observations. The estimated average global ADREs and errors at the top-of-atmosphere (TOA) and the surface were −2.36 ± 0.54 and −4.78 ± 2.2 Wm−2, respectively. In regions with higher dust, pollution, and smoke aerosol loading, the ADREs exhibited significant seasonal variability. In the Sahara and Arabian deserts, during the June-July-August season with higher dust aerosol loading, the seasonal average ADREs in the region were −3.23 and −21.37 Wm−2 at the TOA and surface, respectively. In the Indian region, during the March–April–May season with higher pollution aerosol loading, the ADREs were −10.33 and −28.04 Wm−2 at the TOA and surface, respectively. In Southern Africa, the smoke aerosol with a single-scattering albedo of 0.87 caused negative radiative effects at the TOA, and during the September-October-November season with higher smoke aerosol loading, the seasonal average ADREs were −2.34 and −6.36 Wm−2 at the TOA and surface, respectively. [ABSTRACT FROM AUTHOR]

This study investigates the impacts of high PM10 concentrations on respiratory diseases in Canakkale, Turkey. Daily mean high-PM10 values (> 100 µg m−3) and daily total numbers of chronic obstructive pulmonary disease (COPD) and pneumonia patients are selected for different sexes and age groups (children, adults, and elderly) during the period 2007–2017. Mainly five different source regions of high-PM10 concentration levels are found as a result of implementation of Ward's minimum clustering technique to HYSPLIT 72-h backward trajectory. From 104 days, 19.2% are categorized as internal sources and are positively linked to COPD in female—adult and elderly patients at lag2 and lag3. The other sources are exhibited as external sources and originated from Europe, Sahara, Mediterranean, and Russia regions with the 34.6%, 22.1%, 13.5%, and 10.6% percentages of all episodes, respectively. During Europe-originated high-PM10 days, anthropogenic pollutants mainly cause an increase in the numbers of the elderly female (r = 0.55) and adult male pneumonia patients (r = 0.39) at lag5. Additionally, accompanied by the interaction between Genoa cyclone and surface high over Caspian Sea, natural dust particles are transferred from Sahara to Canakkale by strong southwesterly winds. As a consequence, obvious increases are shown in hospital admissions based on adult female COPD patients at lag1 (r = 0.50) and lag4 (r = 0.53). While Mediterranean origin particulate matter triggering the numbers of COPD and pneumonia-related diseases at lag2 and lag3, the region is exposed to more pneumonia diseases 2 days after arriving of Russia origin harmful pollutants. [ABSTRACT FROM AUTHOR]

Abstract: The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36 h from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, capturing the signature of a severe Saharan dust outbreak episode. The data clearly reveal the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5 km above ground level (a.g.l.) and an upper layer extending between 3.0 and 6.0 km a.g.l. The time evolution of the dust cloud is illustrated and discussed in the paper in terms of several optical parameters (particle backscatter ratio at 532 and 1064 nm, the colour ratio and the backscatter Angström parameter). An inversion algorithm was used to retrieve particle size and microphysical parameters, i.e., mean and effective radius, number, surface area, volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution (PSD), from the multi-wavelength lidar data of particle backscattering, extinction and depolarization. The retrieval scheme employs Tikhonov’s inversion with regularization and makes use of kernel functions for randomly oriented spheroids. Size and microphysical parameters of dust particles are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the presence of a fine mode with radii of 0.1–0.2 μm and a coarse mode with radii of 3–5 μm both in the lower and upper dust layers, and the dominance in the upper dust layer of a coarse mode with radii of 4–5 μm. Effective radius varies with altitude in the range 0.1–1.5 μm, while volume concentration is found to not exceed 92 μm3 cm−3. The real and imaginary part of the complex refractive index vary in the range 1.4–1.6 and 0.004–0.008, respectively. [Copyright &y& Elsevier]

Abstract: In Ghana, a dust-laden Harmattan wind blows from the Sahara from November to March. Some of the dust is trapped in the vegetation, in the lakes and other inland waters, while the rest is blown further away into the Ivory Coast or into the Atlantic Ocean. Several methods have been used to trap the Harmattan dust, mainly bowls with or without water, but also plates or sheets of various materials have been used. This paper compares three different methods to trap the Harmattan dust and describes the differences in amount and particle size distribution of dust trapped in various agroecological zones. The investigation shows that bowls with water trap more dust than plastic mats with 1.5 cm straw which again trap more dust than wooden plates. The bowl values can be used as a measure of the total Harmattan dust deposition, the mat values can be used as a measure of how much Harmattan dust is retained by vegetation, while the plates provide a measure of how much dust is retained on vegetation free areas. The amount of Harmattan dust captured is largest in the north, the amount of dust retained differs significantly from year to year, and a severe Harmattan in the north is not necessary coincident with severe Harmattan in the south. The dust particle size becomes finer towards the south and with increasing amounts of organic matter, and the particle size distribution shows that the major part of the dust trapped is long-term suspended material with a significant input of local dust. The dust particle size is coarser on the mats than in the bowls due to re-suspension from the mats. The presence of diatoms in the samples from Bawku indicates that a substantial part of the dust originates from former lakes in the Sahara. The amount of dust retained in the north gives a deposition rate of about 15 mm per 1000 years. This may explain why loess layers have not developed in Ghana. [Copyright &y& Elsevier]

On June 29–30, 2019, the Barcelona Dust Forecast Center with Non‐hydrostatic Multiscale Model (NMMB/BSC‐Dust) and the Navy Aerosol Analysis and Prediction System forecasted huge amounts of mineral dust over Poland. The Hybrid Single Particle Lagrangian Integrated Trajectory model confirmed uniquely fast (120 hr) long‐range air‐mass transport form North Africa to Poland. This remarkable dust event was observed using lidar at the Aerosol, Clouds and Trace Gases Research InfraStructure site in Warsaw, Central Poland; the only site equipped with Raman‐Mie polarization water vapor lidar in East‐Central Europe. The excellent capabilities of PollyXT lidar allowed to obtain an impressive number of 31 full sets of aerosol optical properties profiles, which enabled study of dust properties evolution on a rare hourly scale. The analyses were completed with the separation of fine and coarse mode dust particles form non‐dust particles using the POlarization‐LIdar PHOtometer Networking algorithm. Huge amount of an exceptionally pure mineral dust from Sahara measured in the free troposphere was characterized by a gradually decreasing coarse dust fraction (76%–21%) with a peak of fine dust fraction (67%) and particle linear depolarization ratio (26%) in the middle of the event. Within the boundary layer, a local urban dust mixed with pollution was observed with fine mode dust particles dominating (44%) and lower particle linear depolarization ratio (7.4%). The influx of pure mineral dust has been unique to this geographical region and will therefore be a reference point for future research and comparative studies. Key Points: Unusually fast, uniform, and quasi‐stable pure mineral dust inflow form Sahara Desert to East‐Central EuropeAdvected Saharan dust composed of significant fractions of fine and coarse mode dust particles evolving in timeLocal urban/agro dust with no evidence of coarse mode particles [ABSTRACT FROM AUTHOR]

Primary ice formation in mixed-phase clouds is initiated by a minute subset of the ambient aerosol population, called ice-nucleating particles (INPs). The knowledge about their atmospheric concentration, composition, and source in cloud-relevant environments is still limited. During the 2017 joint INUIT/CLACE (Ice Nuclei research UnIT/CLoud–Aerosol Characterization Experiment) field campaign, observations of INPs as well as of aerosol physical and chemical properties were performed, complemented by source region modeling. This aimed at investigating the nature and sources of INPs. The campaign took place at the High-Altitude Research Station Jungfraujoch (JFJ), a location where mixed-phase clouds frequently occur. Due to its altitude of 3580 m a.s.l., the station is usually located in the lower free troposphere, but it can also receive air masses from terrestrial and marine sources via long-range transport. INP concentrations were quasi-continuously detected with the Horizontal Ice Nucleation Chamber (HINC) under conditions representing the formation of mixed-phase clouds at -31 ∘C. The INP measurements were performed in parallel to aerosol measurements from two single-particle mass spectrometers, the Aircraft-based Laser ABlation Aerosol MAss Spectrometer (ALABAMA) and the laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). The chemical identity of INPs is inferred by correlating the time series of ion signals measured by the mass spectrometers with the time series of INP measurements. Moreover, our results are complemented by the direct analysis of ice particle residuals (IPRs) by using an ice-selective inlet (Ice-CVI) coupled with the ALABAMA. Mineral dust particles and aged sea spray particles showed the highest correlations with the INP time series. Their role as INPs is further supported by source emission sensitivity analysis using atmospheric transport modeling, which confirmed that air masses were advected from the Sahara and marine environments during times of elevated INP concentrations and ice-active surface site densities. Indeed, the IPR analysis showed that, by number, mineral dust particles dominated the IPR composition (∼58 %), and biological and metallic particles are also found to a smaller extent (∼10 % each). Sea spray particles are also found as IPRs (17 %), and their fraction in the IPRs strongly varied according to the increased presence of small IPRs, which is likely due to an impact from secondary ice crystal formation. This study shows the capability of combining INP concentration measurements with chemical characterization of aerosol particles using single-particle mass spectrometry, source region modeling, and analysis of ice residuals in an environment directly relevant for mixed-phase cloud formation. [ABSTRACT FROM AUTHOR]

We derived two observation-based global monthly mean dust aerosol optical depth (DAOD) climatological datasets from 2007 to 2019 with a 2 ∘ (latitude) × 5 ∘ (longitude) spatial resolution, one based on Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the other on Moderate Resolution Imaging Spectroradiometer (MODIS) observations. In addition, the CALIOP climatological dataset also includes dust vertical extinction profiles. Dust is distinguished from non-dust aerosols based on particle shape information (e.g., lidar depolarization ratio) for CALIOP and on dust size and absorption information (e.g., fine-mode fraction, Ångström exponent, and single-scattering albedo) for MODIS, respectively. The two datasets compare reasonably well with the results reported in previous studies and the collocated Aerosol Robotic Network (AERONET) coarse-mode AOD. Based on these two datasets, we carried out a comprehensive comparative study of the spatial and temporal climatology of dust. On a multi-year average basis, the global (60 ∘ S–60 ∘ N) annual mean DAOD is 0.032 and 0.067 according to CALIOP and MODIS retrievals, respectively. In most dust-active regions, CALIOP DAOD generally correlates well (correlation coefficient R>0.6) with the MODIS DAOD, although the CALIOP value is significantly smaller. The CALIOP DAOD is 18 %, 34 %, 54 %, and 31 % smaller than MODIS DAOD over the Sahara, the tropical Atlantic Ocean, the Caribbean Sea, and the Arabian Sea, respectively. Applying a regional specific lidar ratio (LR) of 58 sr instead of the 44 sr used in the CALIOP operational retrieval reduces the difference from 18 % to 8 % over the Sahara and from 34 % to 12 % over the tropical Atlantic Ocean. However, over eastern Asia and the northwestern Pacific Ocean (NWP), the two datasets show weak correlation. Despite these discrepancies, CALIOP and MODIS show similar seasonal and interannual variations in regional DAOD. For dust aerosol over the NWP, both CALIOP and MODIS show a declining trend of DAOD at a rate of about 2 % yr -1. This decreasing trend is consistent with the observed declining trend of DAOD in the southern Gobi Desert at a rate of 3 % yr -1 and 5 % yr -1 according to CALIOP and MODIS, respectively. The decreasing trend of DAOD in the southern Gobi Desert is in turn found to be significantly correlated with increasing vegetation and decreasing surface wind speed in the area. [ABSTRACT FROM AUTHOR]

Phosphorus contained in atmospheric mineral dust aerosol originating from Africa fertilizes tropical forests in Amazonia. However, the mechanisms influencing this nutrient transport pathway remain poorly understood. Here we use the Community Earth System Model to investigate how large-scale deforestation affects mineral dust aerosol transport and deposition in the tropics. We find that the surface biophysical changes that accompany deforestation produce a warmer, drier, and windier surface environment that perturbs atmospheric circulation and enhances long-range dust transport from North Africa to the Amazon. Tropics-wide deforestation weakens the Hadley circulation, which then leads to a northward expansion of the Hadley cell and increases surface air pressure over the Sahara Desert. The high pressure anomaly over the Sahara, in turn, increases northeasterly winds across North Africa and the tropical North Atlantic Ocean, which subsequently increases dust transport to the South American continent. We estimate that the annual atmospheric phosphorus deposition from dust significantly increases by 27% (P < 0.01) in the Amazon under a scenario of complete deforestation. These interactions exemplify how land surface changes can modify tropical nutrient cycling, which, in turn, may have consequences for long-term changes in tropical ecosystem productivity and biodiversity. [ABSTRACT FROM AUTHOR]

The deposited dose in the human respiratory tract and its influencing factors were investigated for 8 urban/suburban locations within Greek cities. A dosimetry model (ExDoM2) was implemented assuming a 24-h exposure scenario to ambient PM10 whereby regional deposition rates were obtained. Simulations were performed considering three cases (Sahara dust, cold, and warm periods) with seasonal and diurnal variations examining the relative sources and other influencing factors in each case. Health risk indexes such as the relative risk and attributable fraction were also estimated. Overall, higher daily deposited dose was obtained for all urban compared with suburban locations (p < 0.05) and for cold compared with the warm periods (252–820 μg for cold period and 300–686 μg for warm period) for all locations. This finding was associated with increased deposition rate on cold period during evening/night hours, as a result of significant heating emissions. Besides that, most of the urban locations showed relative comparable deposition rates during the day, compared with the daily mean, for the two periods (cold and warm), indicating that urban-associated sources such as exhaust emissions and road dust resuspension contribute similarly to the deposited dose irrespectively of the season. Finally, the highest deposited dose was obtained during Sahara dust events ranged from 1881 to 4648 μg. [ABSTRACT FROM AUTHOR]

Mineral dust emissions from Saharan sources have an impact on the atmospheric environment and sedimentary units in distant regions. Here, we present the first systematic observations of long-range Saharan dust transport towards Iceland. Fifteen Saharan dust episodes were identified to have occurred between 2008 and 2020 based on aerosol optical depth data, backward trajectories and numerical models. Icelandic samples from the local dust sources were compared with deposited dust from two severe Saharan dust events in terms of their granulometric and mineralogical characteristics. The episodes were associated with enhanced meridional atmospheric flow patterns driven by unusual meandering jets. Strong winds were able to carry large Saharan quartz particles (> 100 µm) towards Iceland. Our results confirm the atmospheric pathways of Saharan dust towards the Arctic, and identify new northward meridional long-ranged transport of giant dust particles from the Sahara, including the first evidence of their deposition in Iceland as previously predicted by models. [ABSTRACT FROM AUTHOR]