Atmospheric Dust Loading Research Articles

Global distribution of mineral dust and its impact on radiative fluxes as simulated by WRF-Chem

Dust aerosols make a considerable contribution to the climate system and atmospheric hydrological cycle through their radiative and ice nuclei effects. This underlines the need for investigating the sources of dust aerosols, their transport pathways, and radiative forcing. Seasonal distribution of mineral dust around the globe and its impact on radiation fluxes is estimated using two simulations: a model setup that did not include dust aerosols; and an interactive experiment that included dust aerosols and their feedback to the atmosphere. Simulations were performed by the Weather Research and Forecasting with Chemistry (WRF-Chem) model for a 1-year period. The global annual mean dust optical depth (DOD) at 0.55 $$\upmu$$ m is estimated to be 0.057, with a spring peak value of 0.081 and an autumn minimum value of 0.039. Seasonal variation of atmospheric dust loading is shown to be associated with similar significant variation in shortwave and longwave direct radiation perturbation by dust, both at the surface and top of the atmosphere (TOA). The presence of mineral dust in the interactive simulation is estimated to exert a maximum net direct radiation perturbation in summer with values of $$-$$ 2.85 and $$-$$ 1.63 W m $$^{-2}$$ in clear-sky conditions at the surface and TOA, respectively. It also exerts a global annual net direct radiation perturbation of $$-$$ 1.86 and $$-$$ 1.09 W m $$^{-2}$$ at the surface and TOA, respectively. The surface cooling is attributed to the extinction of incoming solar radiation by dust aerosols, while negative perturbation at the TOA (which demonstrates cooling of the Earth-atmosphere system) is predominantly attributed to an increase in outgoing shortwave radiation.

Impact of Sahara dust on solar radiation at Cape Verde Islands derived from MODIS and surface measurements

Based on radiometer measurements of solar irradiance (direct and diffuse light) and Aeronet-based aerosol optical depth (AOD) obtained at the Cape Verde atmospheric observatory during a major cloud-free dust outbreak event on February 7, 2012, the relationship between Saharan mineral dust outbreaks and a reduction of solar irradiance is quantified. The investigation is representative of the eastern subtropical North Atlantic region where the wind mobilization of mineral desert dust from the Sahara results in aerosol signals that are large enough to outweigh those from other aerosol types such as anthropogenic and marine aerosols. Ground-based estimates of AOD show frequency dependence as is expected from Mie theory. Our AOD signals agree well with satellite-based MODIS products and reveal AOD values exceeding 2.5 during the investigated dust storm event. We also demonstrate the use of satellite imagery with an atmospheric trajectory model to simulate time series of measurements at a given location. Using this approach, variations in AOD observed during February 7, 2012 can be rationalized as spatial inhomogeneities in the atmospheric dust load being advected laterally over the observing site. Our measurements suggest a dust forcing efficiency of around −90W/m2/AOD at a wavelength of 380nm, which is about 10–15% greater than reported in the literature indicative of a possible non-linear behavior at high AODs.

Electrical Conductivity during the Ablation Process of the Glacier No. 1 at the Headwaters of the Urumqi River in the Tianshan Mountains

Electrical conductivity (EC) in aerosols, snow, and meltwater were evaluated at the headwater of the Urumqi River during the ablation seasons of 2003–2008. The results show that EC in meltwater can indicate the intensity of glacier ablation, which negatively correlated with air temperature and discharge. During the early ablation period, EC presents a fluctuation trend and runoff may be primarily from snow, frozen soil, and groundwater. EC decreases to the lowest level during the peak-flow period and runoff flows rapidly through a hydrological system predominantly in ice-walled conduits. EC increases to the highest level during the late ablation period, and runoff transports slowly through a distributed hydrological system at the ice-rock interface. EC in meltwater is far greater than in aerosols, surface snow, and precipitation, which are closely related to atmospheric circulation and dust loading. EC in snow pits denote the spatial variation of snow melting, the enrichment and loss of dissolved ions, and are affected by air temperature. The key ions to determine EC in meltwater are HCO3 -, Ca2+ and SO4 2-, and its dominant control might be biogeochemical pyrite oxidation coupled with calcite and/or dolomite dissolution.

Dissolved aluminium in the ocean conveyor of the West Atlantic Ocean: Effects of the biological cycle, scavenging, sediment resuspension and hydrography

The concentrations of dissolved aluminium (dissolved Al) were studied along the West Atlantic GEOTRACES GA02 transect from 64°N to 50°S. Concentrations ranged from ~0.5nmolkg−1 in the high latitude surface waters to ~48nmolkg−1 in surface waters around 25°N. Elevated surface water concentrations due to atmospheric dust loading have little influence on the deep water distribution. However, just below the thermocline, both Northern and Southern Hemisphere Subtropical Mode Waters are elevated in Al, most likely related to atmospheric dust deposition in the respective source regions.In the deep ocean, high concentrations of up to 35nmolkg−1 were observed in North Atlantic Deep Water as a result of Al input via sediment resuspension. Comparatively low deep water concentrations were associated with water masses of Antarctic origin. During water mass advection, Al loss by scavenging overrules input via remineralisation and sediment resuspension at the basin wide scale. Nevertheless, sediment resuspension is more important than previously realised for the deep ocean Al distribution and even more intensive sampling is needed in bottom waters to constrain the spatial heterogeneity in the global deep ocean.This thus far longest (17,500km) full depth ocean section shows that the distribution of Al can be explained by its input sources and the combination of association with particles and release from those particles at depth, the latter most likely when the particles remineralise. The association of Al with particles can be due to incorporation of Al into biogenic silica or scavenging of Al onto biogenic particles. The interaction between Al and biogenic particles can lead to the coupled cycling of Al and silicate that is observed in some ocean regions. However, in other regions this coupling is not observed due to (i) advective processes bringing in older water masses that are depleted in Al, (ii) unfavourable scavenging conditions in the water column, (iii) low surface concentrations of Al or (iv) additional Al sources, notably sediment resuspension.

Retrieval of dust storm aerosols using an integrated Neural Network model

Dust storms are known to have adverse effects on public health. Atmospheric dust loading is also one of the major uncertainties in global climatic modeling as it is known to have a significant impact on the radiation budget and atmospheric stability. This study develops an integrated model for dust storm detection and retrieval based on the combination of geostationary satellite images and forward trajectory model. The proposed model consists of three components: (i) a Neural Network (NN) model for near real-time detection of dust storms; (ii) a NN model for dust Aerosol Optical Thickness (AOT) retrieval; and (iii) the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to analyze the transports of dust storms. These three components are combined using an event-driven active geo-processing workflow technique. The NN models were trained for the dust detection and validated using sunphotometer measurements from the AErosol RObotic NETwork (AERONET). The HYSPLIT model was applied in the regions with high probabilities of dust locations, and simulated the transport pathways of dust storms. This newly automated hybrid method can be used to give advance near real-time warning of dust storms, for both environmental authorities and public. The proposed methodology can be applied on early warning of adverse air quality conditions, and prediction of low visibility associated with dust storm events for port and airport authorities.

A multi-scale hybrid neural network retrieval model for dust storm detection, a study in Asia

Dust storms are known to have adverse effects on human health and significant impact on weather, air quality, hydrological cycle, and ecosystem. Atmospheric dust loading is also one of the large uncertainties in global climate modeling, due to its significant impact on the radiation budget and atmospheric stability. Observations of dust storms in humid tropical south China (e.g. Hong Kong), are challenging due to high industrial pollution from the nearby Pearl River Delta region. This study develops a method for dust storm detection by combining ground station observations (PM10 concentration, AERONET data), geostationary satellite images (MTSAT), and numerical weather and climatic forecasting products (WRF/Chem). The method is based on a hybrid neural network (NN) retrieval model for two scales: (i) a NN model for near real-time detection of dust storms at broader regional scale; (ii) a NN model for detailed dust storm mapping for Hong Kong and Taiwan. A feed-forward multilayer perceptron (MLP) NN, trained using back propagation (BP) algorithm, was developed and validated by the k-fold cross validation approach. The accuracy of the near real-time detection MLP-BP network is 96.6%, and the accuracies for the detailed MLP-BP neural network for Hong Kong and Taiwan is 74.8%. This newly automated multi-scale hybrid method can be used to give advance near real-time mapping of dust storms for environmental authorities and the public. It is also beneficial for identifying spatial locations of adverse air quality conditions, and estimates of low visibility associated with dust events for port and airport authorities.

Planetary Exploration; Mars on the Scope

This article summarizes a practical case of introduction to research and planetary exploration through the analysis of data from the Rover Environmental Monitoring Station (REMS), one of the ten scientific instruments on board the Curiosity rover of the Mars Science Laboratory (MSL), currently operating at the impact crater Gale, on Mars. It is the main aim of this work to show how the data that are publicly available at the Planetary Data System (PDS) can be used to introduce undergraduate students and the general public into the subject of surface exploration and the environment of Mars. In particular, the goal of this practice was to investigate and quantify the heat-flux between the rover spacecraft and the Martian surface, the role of the atmosphere in this interaction, and its dependence with seasons, as well as to estimate the thermal contamination of the Martian ground produced by the rover. The ground temperature sensor (GTS) of the REMS instrument has measured in-situ, for the first time ever, the diurnal and seasonal variation of the temperature of the surface on Mars along the rover traverse. This novel study shows that the rover radiative heat flux varies between 10 and 22 W/m2 during the Martian year, which is more than 10% of the solar daily averaged insolation at the top of the atmosphere. In addition, it is shown that the radiative heat flux from the rover to the ground varies with the atmospheric dust load, being the mean annual amplitude of the diurnal variation of the surface temperature of 76 K, as a result of solar heating during the day and infrared cooling during the night. As a remarkable and unexpected outcome, it has been established that the thermal contamination produced by the rover alone induces, on average, a systematic shift of 7.5 K, which is indeed about 10% of the one produced by solar heating. This result may have implications for the design and operation of future surface exploration probes such as Insight.

An automated and integrated framework for dust storm detection based on ogc web processing services

Abstract. Dust storms are known to have adverse effects on public health. Atmospheric dust loading is also one of the major uncertainties in global climatic modelling as it is known to have a significant impact on the radiation budget and atmospheric stability. The complexity of building scientific dust storm models is coupled with the scientific computation advancement, ongoing computing platform development, and the development of heterogeneous Earth Observation (EO) networks. It is a challenging task to develop an integrated and automated scheme for dust storm detection that combines Geo-Processing frameworks, scientific models and EO data together to enable the dust storm detection and tracking processes in a dynamic and timely manner. This study develops an automated and integrated framework for dust storm detection and tracking based on the Web Processing Services (WPS) initiated by Open Geospatial Consortium (OGC). The presented WPS framework consists of EO data retrieval components, dust storm detecting and tracking component, and service chain orchestration engine. The EO data processing component is implemented based on OPeNDAP standard. The dust storm detecting and tracking component combines three earth scientific models, which are SBDART model (for computing aerosol optical depth (AOT) of dust particles), WRF model (for simulating meteorological parameters) and HYSPLIT model (for simulating the dust storm transport processes). The service chain orchestration engine is implemented based on Business Process Execution Language for Web Service (BPEL4WS) using open-source software. The output results, including horizontal and vertical AOT distribution of dust particles as well as their transport paths, were represented using KML/XML and displayed in Google Earth. A serious dust storm, which occurred over East Asia from 26 to 28 Apr 2012, is used to test the applicability of the proposed WPS framework. Our aim here is to solve a specific instance of a complex EO data and scientific model integration problem by using a framework and scientific workflow approach together. The experimental result shows that this newly automated and integrated framework can be used to give advance near real-time warning of dust storms, for both environmental authorities and public. The methods presented in this paper might be also generalized to other types of Earth system models, leading to improved ease of use and flexibility.

Variability of the martian seasonal CO2 cap extent over eight Mars Years

We present eight Mars Years of nearly continuous tracking of the CO2 seasonal cap edges from Mars Year (MY) 24 to 31 using Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and Mars Reconnaissance Orbiter (MRO) Mars Climate Sounder (MCS) thermal infrared data. Spatial and temporal resolutions are 1 pixel per degree and 10°Ls (aerocentric longitude of the Sun). The seasonal caps are defined as the regions where the diurnal radiometric temperature variations at ∼32μm wavelength do not exceed 5K. With this definition, terrains with small areal fraction of defrosted regolith able to experience measurable diurnal temperature cycles are not mapped as part of the cap. This technique is adequate to distinguish CO2 from H2O ices, and effective during the polar night or under low illumination conditions. The present analysis answers outstanding questions stemming from fragmented observations at visible wavelengths: (1) the previously sparsely documented growth of the North seasonal caps (160°<Ls<270°) is shown to be repeatable within 1–2° equivalent latitude, and monotonic over the MY 24–31 time period; high repeatability is observed during the retreat of the caps in non-dusty years (∼1° or less equivalent latitude); (2) the MY 25 storm does not seem to have impacted the growth rate, maximal extents, or recession rate of the North seasonal caps, whereas the MY 28 dust storm clearly sped up the recession of the cap (∼2° smaller on average after the storm, during the recession, compared to other years); (3) during non-dusty years, the growth of the South seasonal cap (350°<Ls<100°) presents noticeable variability (up to ∼4° equivalent latitude near Ls=20°) with a maximum extent reached near Ls=90°; (4) the retreat of the Southern seasonal cap (100°<Ls<310°) exhibits large inter-annual variability, especially near 190°<Ls<220°; (5) the recession of the MY 25 South seasonal cap is significantly accelerated during the equinox global dust storm, with surface temperatures suggesting increased patchiness or enhanced dust mantling on the CO2 ice. These results suggest that atmospheric temperatures and dust loading are the primary source of variability in an otherwise remarkably repeatable cycle of seasonal cap growth and recession.

Soil Wind Erodibility Based on Dry Aggregate‐Size Distribution in the Tarim Basin

The Tarim Basin is an important source of airborne particulate matter that contributes to poor air quality in China. However, little attention has been given to estimating wind erodibility of soils in the region. The objective of this study was to determine the soil wind erodibility for four land use types in the Tarim Basin. Wind erodibility was determined from the dry aggregate size distribution of soils collected from desert, farmland, forest, and shrubland environments in spring 2013. Our analysis revealed that the percentage of soil mass composed of aggregates &lt;840 μm in diameter (erodible fraction) ranged from 5.2 to 99.9% across sites with a mean of 58.9% across land use types. The four land use types had a high content of erodible aggregates. The mean percentage of soil mass which was comprised of saltation‐size (500–100 μm in diameter) and suspension‐size material (&lt;100 μm in diameter) was 15.0 and 39.0%, respectively, across land use types. The desert had the highest potential for saltation activity and suspension. Our results suggest that all land use types examined in this study have potential to contribute to the atmospheric dust load in the Tarim Basin and to transcontinental and transoceanic transport of dust.

A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

Due to their outstanding resolution and well-constrained chronologies, Greenland ice-core records provide a master record of past climatic changes throughout the Last Interglacial–Glacial cycle in the North Atlantic region. As part of the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project, protocols have been proposed to ensure consistent and robust correlation between different records of past climate. A key element of these protocols has been the formal definition and ordinal numbering of the sequence of Greenland Stadials (GS) and Greenland Interstadials (GI) within the most recent glacial period. The GS and GI periods are the Greenland expressions of the characteristic Dansgaard–Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. We present here a more detailed and extended GS/GI template for the whole of the Last Glacial period. It is based on a synchronization of the NGRIP, GRIP, and GISP2 ice-core records that allows the parallel analysis of all three records on a common time scale. The boundaries of the GS and GI periods are defined based on a combination of stable-oxygen isotope ratios of the ice (δ18O, reflecting mainly local temperature) and calcium ion concentrations (reflecting mainly atmospheric dust loading) measured in the ice. The data not only resolve the well-known sequence of Dansgaard–Oeschger events that were first defined and numbered in the ice-core records more than two decades ago, but also better resolve a number of short-lived climatic oscillations, some defined here for the first time. Using this revised scheme, we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the Last Glacial period that are represented in the Greenland ice records. The final product constitutes an extended and better resolved Greenland stratotype sequence, against which other proxy records can be compared and correlated. It also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations.

Solar Cooking in the Sahel

Solar cookers have the potential to help many of the world's poorest people, but the availability of sunshine is critical, with clouds or heavy atmospheric dust loads preventing cooking. Using wood for cooking leads to deforestation and air pollution that can cause or exacerbate health problems. For many poor people, obtaining wood is either time-consuming or expensive. Where conflicts have led to displaced people, wood shortages can become acute, leading to often violent clashes between locals and refugees. For many refugee women, this makes collecting wood a high-risk activity.For eight years, Agrometeorological Applications Associates and TchadSolaire (AAA/TS) have been training refugees to manufacture and use solar cookers in northeastern Chad, where there are more than 240,000 refugees. Solar cookers are cheap and simple to make. They are clean and safe, greatly reduce the need for wood, reduce conf licts, reduce the time girls spend collecting wood (thus favoring education), and allow pasteurization of water. Around 140,000 people in the area are now eating solar-cooked food.Using long-term records of direct sunshine from routine surface measurements and aerosol retrievals from SEVIRI on board Meteosat, we present a climatology of conditions suitable for solar cooking in North Africa and West Africa. Solar cookers could be widely used, on an average of about 90% of days in some locations, with large seasonal and spatial variations from changing solar elevations, dustiness, and cloudiness. The climatology will facilitate the future distribution of solar cookers by organizations such as AAA/TS, who work using high-tech information to improve the lives of millions utilizing simple technologies.

Organic matter matters for ice nuclei of agricultural soil origin

Abstract. Heterogeneous ice nucleation is a crucial process for forming ice-containing clouds and subsequent ice-induced precipitation. The importance for ice nucleation by airborne desert soil dusts composed predominantly of minerals is widely acknowledged. However, the potential influence of agricultural soil dusts on ice nucleation has been poorly recognized, despite recent estimates that they may account for up to 20–25% of the global atmospheric dust load. We have conducted freezing experiments with various dusts, including agricultural soil dusts derived from the largest dust-source region in North America. Here we show evidence for the significant role of soil organic matter (SOM) in particles acting as ice nuclei (IN) under mixed-phase cloud conditions. We find that the ice-nucleating ability of the agricultural soil dusts is similar to that of desert soil dusts, but is clearly reduced after either H2O2 digestion or dry heating to 300 °C. In addition, based on chemical composition analysis, we demonstrate that organic-rich particles are more important than mineral particles for the ice-nucleating ability of the agricultural soil dusts at temperatures warmer than about −36 °C. Finally, we suggest that such organic-rich particles of agricultural origin (namely, SOM particles) may contribute significantly to the ubiquity of organic-rich IN in the global atmosphere.

Seasonal and diurnal variations in dust characteristics on the northern slopes of the Tien Shan – Grain-size, mineralogy, chemical signatures and isotope composition of attached nitrate

A dust monitoring program was initiated in the summer of 2010 to (i) improve the informative value of aeolian components of varved lake sediments in Central Asia for palaeoclimatic interpretations, (ii) evaluate the impact of aeolian influx on modern lakes in the region and (iii) obtain data for a future comparison with dust east of the high mountain belt formed by the Alay, Pamir, Tien Shan and Altai mountains. We collected the coarse (>2.5μm) dust fraction on the northern slopes of the Tien Shan 42°40′49.69″N, (74°41′37.36″E, 1740m asl) using a high-volume slit-impactor at 3-day sampling intervals. We present data on the mineralogical composition, particle-size distribution, soluble salts and nitrate isotope composition of the collected dust. The short-term and seasonal changes in dust concentration and composition are discussed in the context of high temporal resolution measurements of meteorological parameters and particle counts for 31 grain-size bands.Throughout the study period, CaCO3 was a major dust constituent (average particle frequency 14%). Between July 2010 and October 2012, the average content of soluble salts was 10wt.%; mole percentages of water-leachable anions were 60% NO3, 30% SO4, 10% Cl. Ca was the dominant leachable cation (>90%). The collected dust comprised (i) gypsum which forms pedogenically in the topsoils of arid regions and (ii) secondary gypsum originating from the interaction of sulphuric acid aerosols with CaCO3 in the atmosphere. Variable proportions of (i) and (ii) and the extent of Ca(NO3)2 formation (verified by chemical mass budgets) were documented in the Ca/Sr and Ca/SO4 ratios of the aqueous leachates.The isotopic compositions of the dust nitrate in the majority of the samples clustered between −10 and +10‰ for δ15N[NO3] (VSMOW) and +50 and +100‰ for δ18O[NO3] (Air). The δ18O[NO3] values of a majority of the collected samples exhibited a weak positive correlation with the NO3 load of the collected dust (R2=0.148). The time series of the δ15N[NO3] values varied around a basement level of −6‰, which indicates that NOx from mobile sources is a major precursor of the dust-NO3. The distinct, positive departures from these values correlated with increases in the content of soot. We conclude that the related δ15N[NO3] peaks reflect increased NOx contributions from coal burning. The possible origin of the dust was evaluated using satellite images and backward trajectory calculations for a few example monitoring intervals. Data synthesis in the context of hemispherical atmospheric circulation models, including the data for 2013, the results from ongoing chemical and isotope analyses of the non-soluble solid residues of the collected materials and the statistical handling of an extended data set will further elucidate the relationships involving atmospheric circulation, atmospheric dust load, dust sources and the characteristics of the study region.

Lead isotopes in the Eastern Equatorial Pacific record Quaternary migration of the South Westerlies

The influence of atmospheric dust on climate and biogeochemical cycles in the oceans is well understood but poorly quantified. Glacial atmospheric dust loads were generally greater than those during the Holocene, as shown, for example, by the covariation of dust fluxes in the Equatorial Pacific and Antarctic ice cores. Nevertheless, it remains unclear whether these increases in dust flux were associated with changes in sources of dust, which would in turn suggest variations in wind patterns, climate or paleo-environment. Such questions can be answered using radiogenic isotope tracers of dust provenance.Here, we present a 160-kyr high-precision lead isotope time-series of dust input to the Eastern Equatorial Pacific (EEP) from core ODP Leg 138, Site 849 (0°11.59′ N, 110°31.18′ W). The Pb isotope record, combined with Nd isotope data, rules out contributions from Northern Hemisphere dust sources, north of the Intertropical Convergence Zone, such as Asia or North Africa/Sahara; similarly, eolian sources in Australia, Central America, the Northern Andes and Patagonia appear insignificant based upon the radiogenic isotope data.Fluctuations in Pb isotope ratios throughout the last 160 kyr show, instead, that South America remained the prevailing source of dusts to the EEP. There are two distinct South American Pb isotope end-members, constrained to be located in the south Central Volcanic Zone (CVZ, 22° S – 27.5° S) and the South Volcanic Zone (SVZ, 33° S – 43° S), with the former most likely originating in the Atacama Desert. Dust availability in the SVZ appears to be related to the weathering of volcanic deposits and the development of ash-derived Andosols, and influenced by local factors that might include vegetation cover. Variations in the dust fluxes from the two sources are in phase with both the dust flux and temperature records from Antarctican ice cores. We show that the forcing of dust provenance over time in the EEP overall is influenced by high-southerly-latitude climate conditions, leading to changes in the latitudinal position and strength of the South Westerlies as well as the coastal winds that blow northward along the Chilean margin. The net result is a modulation of dust emission from the Atacama Desert and the SVZ via a northward migration of the South Westerlies during cold periods and southward retreat during glacial terminations.

ВЛИЯНИЕ АТМОСФЕРНЫХ УСЛОВИЙ И ЗАПЫЛЕННОСТИ СРЕДЫ НА СВОЙСТВА КОНСТРУКЦИОННЫХ ОРГАНОПЛАСТИКОВ

ВЛИЯНИЕ АТМОСФЕРНЫХ УСЛОВИЙ И ЗАПЫЛЕННОСТИ СРЕДЫ НА СВОЙСТВА КОНСТРУКЦИОННЫХ ОРГАНОПЛАСТИКОВ

Influence of dust loading on atmospheric ionizing radiation on Mars

Measuring the radiation environment at the surface of Mars is the primary goal of the Radiation Assessment Detector on the NASA Mars Science Laboratory's Curiosity rover. One of the conditions that Curiosity will likely encounter is a dust storm. The objective of this paper is to compute the cosmic ray ionization in different conditions, including dust storms, as these various conditions are likely to be encountered by Curiosity at some point. In the present work, the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety model, recently modified for Mars, was used along with the Badhwar &amp; O'Neill 2010 galactic cosmic ray model. In addition to galactic cosmic rays, five different solar energetic particle event spectra were considered. For all input radiation environments, radiation dose throughout the atmosphere and at the surface was investigated as a function of atmospheric dust loading. It is demonstrated that for galactic cosmic rays, the ionization depends strongly on the atmosphere profile. Moreover, it is shown that solar energetic particle events strongly increase the ionization throughout the atmosphere, including ground level, and can account for the radio blackout conditions observed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on the Mars Express spacecraft. These results demonstrate that the cosmic rays' influence on the Martian surface chemistry is strongly dependent on solar and atmospheric conditions that should be taken into account for future studies.

Late Pleistocene variations of the background aeolian dust concentration in the Carpathian Basin: an estimate using decomposition of grain-size distribution curves of loess deposits

AbstractAeolian dust deposits can be considered as one of the most important archives of past climatic changes. Alternating loess and paleosol strata display variations of the dust load in the Pleistocene atmosphere. By using the observations of recent dust storms, we are able to employ Late Pleistocene stratigraphic datasets (with accurate chronological framework) and detailed granulometric data for making conclusions on the atmospheric dust load in the past. Age-depths models, created from the absolute age data and stratigraphic interpretation, allow us to calculate sedimentation rates and dust fluxes, while grain-size specifies the dry-deposition velocity, i.e. the atmospheric residence time of mineral particles. Thus, the dust concentration can be expressed as the quotient of the dust flux and gravitational settling velocity. Recent observations helped to clarify the mechanisms behind aeolian sedimentation and the physical background of this process has nowadays been well established. Based on these two, main contrasting sedimentary modes of dust transport and deposition can be recognised: the short suspension episodes of the coarse (silt and very fine sand) fraction and the long-range transport of a fine (clay and fine silt) component. Using parametric curve fitting the basic statistical properties of these two sediment populations can be revealed for Pleistocene aeolian dust deposits, as it has been done for loess in Hungary. As we do not have adequate information on the magnitude and frequency of the Pleistocene dust storms, conclusions could only be made on the magnitude of continuous background dust load. The dust concentration can be set in the range between 1100 and 2750 μg/m3. These values are mostly higher than modern dust concentrations, even in arid regions. Another interesting proxy of past atmospheric conditions could be the visibility, being proportional to the dust concentration. According to the known empirical dust concentration – visibility equations, its value is around 6.5 to 26 kilometres.

Aeolian dust deposition rates in Northern French forests and inputs to their biogeochemical cycles

This study describes the Aeolian dust deposition (ADD) in 4 sites of Northern France. Between December 2009 and March 2012, we sampled (i) Aeolian dust every four weeks, and (ii) 6 episodes of forecasted high atmospheric dust load mainly from the Saharan desert, the largest source of Aeolian dust in the world. These samples were treated with oxygen peroxide to remove organic matter so as to only compare the mineral fraction of the samples in the 4 sampling sites and to analyze their mineralogy. The solid samples contained the hardly soluble part of Aeolian dust (H-ADD). Its deposition was of 1.9 ± 0.3 g m−2 year−1 with a seasonal pattern of high deposition from spring to early autumn and a low deposition in winter. H-ADD deposition during the forecasted episodes of high atmospheric load did not systematically exceed the deposition rate during the rest of the sampling period. This indicates that such episodes little contributed to the annual H-ADD rate. The mineralogy revealed a heterogeneous set of minerals dominated by silicates with a common basis of major types (quartz, feldspars, mica, chlorite, kaolinite and interlayered clay minerals in every sample) with randomly trace minerals (Fe-oxides, sulfates, amphibole, talc, gibbsite and carbonates). The chemistry of H-ADD led to a dominant input of Si (up to 4.4 kg ha−1 year−1), while the nutrients inputs of Ca, K, Mg and P from ADD and the atmospheric organics (APD) in openfield were together of 1.5 ± 0.5 kg ha−1 year−1 with a high contribution of soluble minerals and organic matter of ca. 40% for Mg and K, and of ca. 80% for Ca and P. Nutrient inputs from APD are especially an interesting source of P for forests developed on acidic soils.

External supply of dust regulates dust emissions from sand deserts

Abstract Dust emission from the sand desert is an important contributor to long-term atmospheric dust loading. The source of desert dust has been previously attributed to the aeolian abrasion of sand grains during wind-blown sand activities. The abrasion rate, however, tends to decrease as the grain roundness increases with abrasion time, and shows unable to produce an adequate supply of dust to support long-term dust emission. Here we show that an external dust supply is also an important dust contributor to the sand desert, and that dust emission from the sand desert will occur if an external dust supply is available and diminish if the external supply is cut off. Our results relate the dust emission from sand deserts to an external dust supply resulting from disturbed processes or changed hydrological processes caused by climate changes or human activities, and also suggest that the dust emission rate of natural sand deserts can actually increase with external dust supply resulting from human activities or climatic changes, rather than with wind energy alone, as is commonly perceived.