Major Dust Research Articles

Weakened dust activity over China and Mongolia from 2001 to 2020 associated with climate change and land-use management

Dust cycle is actively involved in the Earth’s climate and environmental systems. However, the spatiotemporal pattern and recent trend of dust emission from the drylands in East Asia remain unclear. By calculating dust aerosol optical depth (DOD) from the newly released moderate resolution imaging spectrometer aerosol products, we obtain a relatively long satellite-based time series of dust activity from 2001 to 2020 over China and Mongolia. We identify pronounced interannual variability of dust activity that is consistent with ground-based meteorological observations in the study area. A substantial reduction in spring dust activity in northern China is also found, which seems in accordance with the long-term weakening trend since the 1970s that has been attributed to the wind speed decline by previous studies. However, the spatial pattern of the trends in both annual mean and seasonal dust activity during the last 20 years is divergent, and the most significant dust diminishing is found over north-central China where large-scale vegetation restoration projects have been implemented. It indicates that in addition to the potential contribution of wind speed change, land-use change also plays an important role in the recent inhibition of dust emission. The current results show that dust activity occurs most intensively in spring, followed by summer and relatively weaker in autumn and winter. However, dust activity in autumn and winter has increased significantly in NW China despite the overall decreasing trend in other two seasons, probably associated with different seasonal atmospheric and land surface conditions. Finally, the DOD distribution reveals that the Tarim Basin, Gobi and Qaidam Basin Deserts are three major dust sources in East Asia. Compared to ground observations which are spatially limited and distributed unevenly, remote sensing provides an important complement, and it can serve as reference for identification of dust sources using other methods such as geochemical fingerprint and modeling.

The dust load and radiative impact associated with the June 2020 historical Saharan dust storm

In June 2020, a major dust outbreak occurred in the Sahara that impacted the tropical Atlantic Ocean. In this study, the dust load and radiative forcing of the dust plumes on both the atmosphere and ocean surface is investigated by means of observations and modelling. We estimated dust loadings in excess of 8 Tg over the eastern tropical Atlantic, comparable to those observed over the desert during major Saharan dust storms. The dust induced an up to 1.1 K net warming of the ocean surface and a 1.8K warming of the air temperature (i.e., two to three times the respective climatological standard deviations), with a +14 W m−2 (∼28% of the mean value) increase in the surface net radiation flux at night. As the dust plumes extended all the way to the Caribbean, it is possible that this historical dust event helped fuel the record-breaking 2020 Atlantic hurricane season.

Description of Dust Emission Parameterization in CAS‐ESM2 and Its Simulation of Global Dust Cycle and East Asian Dust Events

AbstractThe dust emission parameterization in the Chinese Academy of Sciences Earth System Model version 2 (CAS‐ESM2) is described with emphasis on the implementation process and simulations of global dust cycle and East Asia dust event statistics. The parameterization is based on the scheme of Shao (2004; http://doi.org/10.1029/2003JD004372) which considers two major dust emission mechanisms, namely, saltation bombardment and aggregation disintegration. Shao (2004; http://doi.org/10.1029/2003JD004372) scheme was well tested against field observations and has been widely used in regional dust modeling. Here this scheme is implemented into a global climate model for the first time and thus provides an independent solution for simulating global dust emissions. With this scheme, CAS‐ESM2 reasonably simulates the main dust emission regions in the Earth and reproduces the observations of dust deposition flux and surface dust concentrations at most stations. Compared to the synoptic records of dust events, the model also captures the general patterns and seasonal variations of dust activities in East Asia. However, the model underestimates the frequency of strong dust events (instantaneous surface dust concentrations >1,000 μg m−3) due to the weaker surface winds simulated by the model. The model tends to simulate much weaker and longer‐lasting dust events in Eastern Sources (35–49°N, 94–126.5°E) of northern China, suggesting the weaker and slower‐moving synoptic weather systems associated with dust events in the model. Overall CAS‐ESM2 performs well in simulating the key aspects of global dust distribution and East Asian dust events, yet some biases remain to be improved.

Hepatic Gene Expression Changes in Rats Internally Exposed to Radioactive 56MnO2 Particles at Low Doses.

We have studied the biological effects of the internal exposure to radioactive manganese-56 dioxide (56MnO2), the major radioisotope dust found in soil after atomic bomb explosions. Our previous study of blood chemistry indicated a possible adverse effect of 56MnO2 on the liver. In the present study, we further examined the effects on the liver by determining changes in hepatic gene expressions. Male Wistar rats were exposed to 56MnO2 particles (three groups with the whole-body doses of 41, 90, and 100 mGy), stable MnO2 particles, or external 60Co γ-rays (2 Gy), and were examined together with the non-treated control group on postexposure day 3 and day 61. No histopathological changes were observed in the liver. The mRNA expression of a p53-related gene, the cyclin-dependent kinase inhibitor 1A, increased in 56MnO2 as well as in γ-ray irradiated groups on postexposure day 3 and day 61. The expression of a stress-responsive gene, nuclear factor κB, was also increased by 56MnO2 and γ-rays on postexposure day 3. However, the expression of cytokine genes (interleukin-6 or chemokine ligand 2) or fibrosis-related TGF-β/Smad genes (Tgfb1, Smad3, or Smad4) was not altered by the exposure. Our data demonstrated that the internal exposure to 56MnO2 particles at less than 0.1 Gy significantly affected the short-term gene expressions in the liver in a similar manner with 2 Gy of external γ-irradiation. These changes may be adaptive responses because no changes occurred in cytokine or TGF-β/Smad gene expressions.

Hf-Nd-Sr Isotopic Composition of the Tibetan Plateau Dust as a Fingerprint for Regional to Hemispherical Transport.

Large areas of arid regions in the Tibetan Plateau (TP) are undergoing desertification and subsequent aeolian emission and transport. The contribution of TP soils to the atmospheric aerosol burden in Asia and elsewhere is not known. Here, we use Hf, Nd, and Sr isotopes to distinguish the TP from other Asian dust-producing regions and compare the signatures to sediments in major dust sink regions. We found that the Hf-Nd-Sr isotopes of TP soils showed unique spatial signatures. From north to south, 87Sr/86Sr ratios gradually increased, while εNd and εHf values gradually decreased; from west to east, 87Sr/86Sr and εHf gradually increased, while εNd changed indistinctly. The Hf-Nd-Sr isotopic compositions of TP soils were controlled by four geographic isotope regions: the northern, southern, western, and eastern TP. Compared with Asian large deserts, the TP showed a unique isotopic composition, which together exhibited a significant spatial change across Asia. Compared to dust isotopes in prominent sink areas, we found that the TP is an important dust source to eastern TP glaciers, the Chinese Loess Plateau, South China Sea, Japan, and Greenland. This study provides clear isotopic evidence that the TP is a major aeolian contributor in the Northern Hemisphere and may have important implications for the global aeolian cycle.

Spatiotemporal variations and long term trends analysis of aerosol optical depth over the United Arab Emirates

This research provides a comprehensive long term time series analysis of the spatiotemporal variability of aerosol optical depth (AOD) over the United Arab Emirates (UAE) using MODIS (Moderate-resolution imaging spectroradiometer) MAIAC (Multi-Angle Implementation of Atmospheric Correction) AOD (aerosol optical depth) product for the period 2003–2018. The UAE is located in one of the driest places on earth, the Arabian Peninsula, with two large extended desert regions that form major atmospheric dust sources in the world. The atmospheric dust emitted by these vast deserts is transported locally and regionally and it is the primary major contributor to the overall aerosol optical depth in this area. The investigation of the spatiotemporal trends of AOD over the UAE showed a significant obvious annual seasonal variability. Results showed a significant increase in AOD during summer due to high wind speed, resulting in scattered events of small to large scale haboobs within the study area, high temperature, and high relative humidity. The increased humidity levels are due to increased temperatures in the summer season leading to significant evaporation from the neighbouring water bodies (mainly the Arabian Gulf and the Sea of Oman) leading to a significant increase in water vapour levels in the atmosphere. Summar AOD values during the study period ranged between 0.42 – 0.73. The second highest AOD was observed in spring followed by winter. Spring AOD values ranged between 0.33-0.58 and winter values ranged between 0.25 – 0.41. The spatial distributions of AOD showed higher values over the coastal and desert areas. Coastal areas portrayed higher values as well likely due to the high levels of evaporation and increased anthropogenic activities such as coastal urban developments and automobile pollution. Time series analysis of the multitemporal dataset confirmed the SARIMA forecast model as the best fit which can be used to provide an accurate and reliable monthly forecast for the AOD concentrations in the UAE.

Atmospheric concentrations and emission ratios of black carbon and nitrogen oxides in the Arabian/Persian Gulf region

The atmospheric concentration of black carbon (BC) has paramount importance worldwide due to its role in global warming and its adverse effect on human health. Only limited information is available about BC concentration and emission factors from the Arabian/Persian Gulf region despite the presence of significant sources including petrochemical industry and maritime shipping. The atmospheric concentrations of BC, nitrogen oxides (NO, NO2), ozone and particulate matter (PM10) were monitored at a suburban location and at a central residential location in Doha, Qatar during fall-spring 2016–2017. Elevated NOX and BC mean concentrations (25.8 ppbv and 5.17 μg/m3 respectively) and maximum values (228 ppbv vs. 27 μg/m3) were measured at both locations. The average ozone mixing ratio was 15.9 ppbv (max. 52.6 ppbv). Typically, the BC concentration was correlated with NOX, which indicates common sources. BC/NOX emission ratios (ER) were calculated to characterise the sources, while the NO/NOX concentration ratio was used as a proxy of pollution age. The calculated BC/NOX emission ratios were found to be high comparing to the EMEP database, with the means of 0.13 μg m−3 ppbv−1 (suburban location) and 0.10 μg m−3 ppbv−1 (residential location). The BC/NOX ER did not show significant daily variation, while the NO/NOX ratio showed typical urban time pattern with high ratio during morning rush hours following by a decreasing trend during afternoon, and minimum values at night-time. The PM10 concentrations were high during the measurement period with a mean of 103 μg m−3, which is typical in the Gulf region. During occasional dust storm events the PM10 hourly average concentration raised peaked at 1054 μg m−3. Significant influence of mineral dust was observed on the BC measurement and the absorption properties, as it was increasing the BC readings and widening the distribution of the absorption Ångström exponent. The mass absorption cross-section of mineral dust was determined during the major dust storm event.

Climatically Modulated Dust Inputs from New Zealand to the Southwest Pacific Sector of the Southern Ocean Over the Last 410 kyr

AbstractEolian mineral dust is an active agent in the global climate system. It affects planetary albedo and can influence marine biological productivity and ocean‐atmosphere carbon dynamics. This makes the understanding of the global dust cycle crucial for constraining the dust/climate relationship, which requires long‐term dust emission records for all major dust sources. Despite their importance, the sources of atmospheric dust deposited in the Southern Ocean remain poorly constrained. Eolian dust in the Pacific sector of the Southern Ocean is generally assumed to originate from Australia, with minor contributions from New Zealand. Here, we present a high‐resolution elemental record of terrestrial inputs for the past ∼410 kyr from marine sediment core PS75/100‐4 recovered from east of South Island, New Zealand. Sediment grain size is slightly finer than that of loess deposits from South Island, New Zealand, and is coarser than that of marine sediments in the Tasman Sea to the west of New Zealand, which indicates that the dust originated mainly from New Zealand and not only from Australia. Core PS75/100‐4 records lithogenic mass accumulation rates ranging from ∼0.01 to 0.69 g/cm2/kyr (∼0.20 g/cm2/kyr average), with variations over a factor of ∼3–4 over glacial versus interglacial timescales for the past 410 kyr. Our geochemical data correlate well with the Southern Ocean and Antarctic eolian dust records and suggest a westerly wind‐supplied dust signal from New Zealand. Our findings, therefore, suggest that New Zealand should be considered an important long‐term regional dust source in global dust cycle models.

Abnormal Phase Structure of Thermal Tides During Major Dust Storms on Mars: Implications for the Excitation Source of High‐altitude Water Ice Clouds

AbstractInteractions among the thermal tide, airborne dust, and water ice clouds significantly influence the Martian atmosphere. The absence of a stratosphere on Mars allows easier identification of the thermal tides from observational data than that on Earth, making Mars a natural laboratory to study the tidal excitation and propagation processes. However, the global tidal phase structure and its response to the tidal excitation sources on Mars have not been studied from observations. Here, we present a comprehensive analysis of the phase structure of migrating diurnal tide (DW1) using multi‐local‐time observations of the Mars Climate Sounder. The DW1 phase at low‐to‐mid latitudes shows a downward phase progression, which indicates upward tidal energy and momentum propagation throughout the year but with an apparent hemispheric asymmetry. The entire DW1 phase structure rises and falls with the dust height at the southern mid‐latitudes suggesting a modulation of vertical dust extent on the altitude of the excitation source. During major regional dust storms, the DW1 phase propagates anomalously upward from 10 to 1 Pa in the Southern hemisphere. The Hough analysis suggests that the DW1 in the dust layer can only propagate upward to 10 Pa while the downward propagating mode above 10 Pa may be excited from a high‐altitude source. Evidence suggests that the enhanced high‐altitude water ice clouds could be a potential excitation source for these downward propagating tidal modes. These findings demonstrate how thermal tides can locally behave like inertia‐gravity waves and the importance of water ice clouds to Martian atmospheric dynamics.

The Influence of Indoor Environmental Factors on the Prevalence of House Dust Mites as Aeroallergens in Bandar Abbas Student Dormitories, South of Iran, 2019.

This study was conducted to determine the influence of environmental factors on the prevalence of house dust mites in student dormitories of Bandar Abbas city. In this study, 64 dust samples were collected from seven randomly selected dormitories located in various areas of the Bandar Abbas. The collected mites were isolated and mounted in Hoyer's medium and identified using a morphological key. The associations between the environmental factors and the density of house dust mites were investigated. In total, 1,093 adult mites were collected and identified. They consisted of four species including Dermatophagoides pteronyssinus Trouessart (57.6%), Dermatophagoides farinae Hughes (24.3%) and Dermatophagoides evansi Fain (14.9%) (Acari: Pyroglyphidae), and Cheyletus malaccensis Oudemans (3.2%) (Acari: Cheyletidae). All of the dormitories were contaminated by more than one house dust mites species and the mean density of house dust mites in dormitories was 8.3 ± 0.2 mites/g of dust. There was a significant relationship between average house dust mites density and some of environmental factors such as relative humidity, temperature, floor covering type, and number of occupants (P < 0.05). Results of this study revealed that two major allergenic dust mites, D. pteronyssinus and D. farinae, were the most prevalent and collected from all of dormitories and some of indoor environmental factors found to influence mites' population.

Dust Storm‐Enhanced Gravity Wave Activity in the Martian Thermosphere Observed by MAVEN and Implication for Atmospheric Escape

AbstractLower atmospheric global dust storms affect the small‐ and large‐scale weather and variability of the whole Martian atmosphere. Analysis of the CO2 density data from the Neutral Gas and Ion Mass Spectrometer instrument on board NASA's Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of gravity wave (GW)‐induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate observationally that, for a 20% and 40% GW‐induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.

Gone with the Wind: Microbial Communities Associated with Dust from Emissive Farmlands.

Dust is a major vehicle for the dispersal of microorganisms across the globe. While much attention has been focused on microbial dispersal in dust plumes from major natural dust sources, very little is known about the fractionation processes that select for the "dust microbiome." The recent identification of highly emissive, agricultural land dust sources in South Africa has provided the opportunity to study the displacement of microbial communities through dust generation and transport. In this study, we aimed to document the microbial communities that are carried in the dust from one of South Africa's most emissive locations, and to investigate the selective factors that control the partitioning of microbial communities from soil to dust. For this purpose, dust samples were generated at different emission sources using a Portable In-Situ Wind Erosion Lab (PI-SWERL), and the taxonomic composition of the resulting microbiomes was compared with the source soils. Dust emission processes resulted in the clear fractionation of the soil bacterial community, where dust samples were significantly enriched in spore-forming taxa. Conversely, little fractionation was observed in the soil fungal communities, such that the dust fungal fingerprint could be used to identify the source soil. Dust microbiomes were also found to vary according to the emission source, suggesting that land use significantly affected the structure and fractionation of microbial communities transported in dust plumes. In addition, several potential biological allergens of fungal origin were detected in the dust microbiomes, highlighting the potential detrimental effects of dust plumes emitted in South Africa. This study represents the first description of the fractionation of microbial taxa occurring at the source of dust plumes and provides a direct link between land use and its impact on the dust microbiome.

Formation of a low‐level barrier jet and its modulation by dust radiative forcing over the Hexi Corridor in Central China on March 17, 2010

AbstractA low‐level barrier jet (LLBJ) formed along the northeast slope of the Tibetan Plateau on March 17, 2010. The LLBJ was accompanied by a major dust event. Numerical simulations conducted with the Weather Research and Forecasting dust (WRF‐dust) model show that the formation of the LLBJ was primarily due to mid‐level, southeastward descent of high momentum air, which impinged on the north slope of the Tibetan Plateau, resulting in ageostrophic flow acceleration under geostrophic adjustment. The LLBJ was reinforced by the Bernoulli effect, where the physical barrier associated with the Tibetan Plateau to the southwest and the virtual barrier associated with sloped, packed isentropic surfaces to the northeast combined to constrict the air flow, thus augmenting the acceleration of the air as it entered the Hexi Corridor. The simulations show that the LLBJ, which stayed close to the western entrance of the Hexi Corridor, gradually descended during the daytime until early evening. During this period, the core of the LLBJ stayed directly above the 302‐K isentropic surface. The LLBJ, which was located to the south of the main dust plume, was modulated by dust radiative heating and cooling. Over the main dust plume, as well as in the LLBJ region, radiative heating of the dust warmed the upper part of the boundary layer and cooled it below, which stabilized the boundary layer, decreased the boundary layer depth, and reduced the vertical mixing, causing the surface winds to weaken. As a consequence of the feedback between the circulation and the dust radiative forcing, the total dust emission was reduced by ∼9.7–11% and peaked 1–2 hr earlier than without dust radiative effects, while the LLBJ's intensity, which was 1–2 m·s−1 stronger, was better maintained within the boundary layer during the daytime until early evening.

Characterizing Dust‐Radiation Feedback and Refining the Horizontal Resolution of the MarsWRF Model Down to 0.5 Degree

AbstractIn this study, three simulations by the Mars Weather Research and Forecasting Model are compared: two 10 Martian year (MY) 2° × 2° simulations with (i) fully radiatively active dust and (ii) a prescribed dust scenario, and a (iii) 1 MY 0.5° × 0.5° simulation with prescribed dust as in (ii). From comparing (i) and (ii), we found that the impact of dust‐radiation feedback is individually different for any region. The most striking evidence are major dust lifting activities to the south of Chryse Planitia (S‐CP) seen in (i) but not in (ii). By contrast, dust lifting and deposition on the southern slopes and inside the Hellas Basin are similar in both simulations. The latter, in turn, points toward a similar near‐surface atmospheric circulation. In (iii), the total global amount of wind stress lifted dust is by a factor of ∼8 higher than in (ii), with S‐CP being a major lifting region as in (i). Nonetheless, the surface dust lifting by wind stress in (iii) may be also reduced regionally, as seen at the peak of Elysium Mons because of its unique topography. The zonal mean circulation in (i) is generally of a comparable strength to that in (ii), with exceptions in global dust storm years, when it is clearly stronger in (i), in line with a dustier atmosphere. The differences in the zonal mean circulation between (ii) and (iii) are mostly at lower altitudes and may arise because of differences in the representation of the topography.

ModIs Dust AeroSol (MIDAS): a global fine-resolution dust optical depth data set

Abstract. Monitoring and describing the spatiotemporal variability in dust aerosols is crucial for understanding their multiple effects, related feedbacks, and impacts within the Earth system. This study describes the development of the ModIs Dust AeroSol (MIDAS) data set. MIDAS provides columnar daily dust optical depth (DOD) at 550 nm at a global scale and fine spatial resolution (0.1∘ × 0.1∘) over a 15-year period (2003–2017). This new data set combines quality filtered satellite aerosol optical depth (AOD) retrievals from MODIS-Aqua at swath level (Collection 6.1; Level 2), along with DOD-to-AOD ratios provided by the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) reanalysis to derive DOD on the MODIS native grid. The uncertainties of the MODIS AOD and MERRA-2 dust fraction, with respect to the AEronet RObotic NETwork (AERONET) and LIdar climatology of vertical Aerosol Structure for space-based lidar simulation (LIVAS), respectively, are taken into account for the estimation of the total DOD uncertainty. MERRA-2 dust fractions are in very good agreement with those of LIVAS across the dust belt in the tropical Atlantic Ocean and the Arabian Sea; the agreement degrades in North America and the Southern Hemisphere, where dust sources are smaller. MIDAS, MERRA-2, and LIVAS DODs strongly agree when it comes to annual and seasonal spatial patterns, with colocated global DOD averages of 0.033, 0.031, and 0.029, respectively; however, deviations in dust loading are evident and regionally dependent. Overall, MIDAS is well correlated with AERONET-derived DODs (R=0.89) and only shows a small positive bias (0.004 or 2.7 %). Among the major dust areas of the planet, the highest R values (&gt;0.9) are found at sites of North Africa, the Middle East, and Asia. MIDAS expands, complements, and upgrades the existing observational capabilities of dust aerosols, and it is suitable for dust climatological studies, model evaluation, and data assimilation.

The Atmospheric Drivers of the Major Saharan Dust Storm in June 2020

AbstractThis study investigates the atmospheric dynamics of the major dust storm that occurred in June 2020 over the Sahara and during which dust clouds associated with the highest‐on‐record aerosol optical depths were transported toward the America. An anomalous atmospheric circulation pattern in the mid‐latitudes, linked to a circumglobal wavetrain, resulted in the development of a subtropical high‐pressure system to the west of the Saharan heat low. This created a pressure dipole and generated anomalously strong northeasterlies over the Sahara, which caused continuous dust emissions over 4 days. Occurring along the northern fringes of the intertropical discontinuity, the dust was transported to higher altitudes (6 km) by the strong updraft in this region. This injected the dust at the African Easterly Jet (AEJ) altitudes and favored a rapid westward long‐range transport. The AEJ was also anomalously strong, being strengthened by the anticyclonic circulation associated with the anomalous high.

Chemical composition and source apportionment of atmospheric aerosols on the Namibian coast

Abstract. The chemical composition of aerosols is of particular importance to assess their interactions with radiation, clouds and trace gases in the atmosphere and consequently their effects on air quality and the regional climate. In this study, we present the results of the first long-term dataset of the aerosol chemical composition at an observatory on the coast of Namibia, facing the south-eastern Atlantic Ocean. Aerosol samples in the mass fraction of particles smaller than 10 µm in aerodynamic diameter (PM10) were collected during 26 weeks between 2016 and 2017 at the ground-based Henties Bay Aerosol Observatory (HBAO; 22∘6′ S, 14∘30′ E; 30 m above mean sea level). The resulting 385 filter samples were analysed by X-ray fluorescence and ion chromatography for 24 inorganic elements and 15 water-soluble ions. Statistical analysis by positive matrix factorisation (PMF) identified five major components, sea salt (mass concentration: 74.7±1.9 %), mineral dust (15.7±1.4 %,), ammonium neutralised (6.1±0.7 %), fugitive dust (2.6±0.2 %) and industry (0.9±0.7 %). While the contribution of sea salt aerosol was persistent, as the dominant wind direction was south-westerly and westerly from the open ocean, the occurrence of mineral dust was episodic and coincided with high wind speeds from the south-south-east and the north-north-west, along the coastline. Concentrations of heavy metals measured at HBAO were higher than reported in the literature from measurements over the open ocean. V, Cd, Pb and Nd were attributed to fugitive dust emitted from bare surfaces or mining activities. As, Zn, Cu, Ni and Sr were attributed to the combustion of heavy oils in commercial ship traffic across the Cape of Good Hope sea route, power generation, smelting and other industrial activities in the greater region. Fluoride concentrations up to 25 µg m−3 were measured, as in heavily polluted areas in China. This is surprising and a worrisome result that has profound health implications and deserves further investigation. Although no clear signature for biomass burning could be determined, the PMF ammonium-neutralised component was described by a mixture of aerosols typically emitted by biomass burning, but also by other biogenic activities. Episodic contributions with moderate correlations between NO3-, nss-SO42- (higher than 2 µg m−3) and nss-K+ were observed, further indicative of the potential for an episodic source of biomass burning. Sea salt accounted for up to 57 % of the measured mass concentrations of SO42-, and the non-sea salt fraction was contributed mainly by the ammonium-neutralised component and small contributions from the mineral dust component. The marine biogenic contribution to the ammonium-neutralised component is attributed to efficient oxidation in the moist marine atmosphere of sulfur-containing gas phase emitted by marine phytoplankton in the fertile waters offshore in the Benguela Upwelling System. The data presented in this paper provide the first ever information on the temporal variability of aerosol concentrations in the Namibian marine boundary layer. This data also provide context for intensive observations in the area.

New Zealand as a source of mineral dust to the atmosphere and ocean

The chemical and isotopic compositions of sediments and dust can be used to trace their provenance, providing insights into many Earth surface processes. During past glacial climates, much of the New Zealand (NZ) South Island was blanketed by erosive glacier systems that produced large volumes of sediment. We estimate the expansion of glacial outwash plains based on a sea level lowering of 130 m at the Last Glacial Maximum (LGM), and find that the Canterbury Plains in the central South Island likely expanded by 30,000 km2, a nearly five-fold increase, while the Southland/southern Otago region may have extended southward to cover an additional ∼45,000 km2, an eight-fold increase of the coastal plain area. Considering NZ’s extreme uplift and erosion rates (∼10 m kyr−1), the South Island, though limited in extent compared to larger Southern Hemisphere landmasses, may serve as an important dust source to the high-latitude atmosphere and ocean.To facilitate accurate tracing of the extent of aeolian and oceanic transport of NZ dust, this study presents major/trace element and Sr-Nd-Pb isotope ratios on sediments from the major present-day dust and sediment producing regions of the South Island. The sediment compositions strongly reflect the regional geology. For example, compared to the central South Island, Nd isotope ratios in the southern South Island are more variable and show younger crustal residence ages. The combined Sr-Nd-Pb isotopic ratios show that the central NZ South Island can be distinguished geochemically from many other Southern Hemisphere dust sources. Although isotopic similarities between the central NZ South Island and more northerly regions of South America, including Central Western Argentina and the Puna-Altiplano Plateau, and Kati Thanda-Lake Eyre in Australia (based on new data in this study) hinder downstream source attribution, a key finding is that these isotopes successfully discriminate NZ from other locations in Australia, such as the Murray-Darling Basin, Northern Territory, and Western Australia, as well as southern Africa and regions of South America south of ∼37°S (Patagonia and Tierra del Fuego). A comparison of the NZ data with East Antarctic ice core dust samples indicates that NZ was not a significant dust supplier to East Antarctica; rather, the East Antarctic dust compositions can be explained by dust supplied by Patagonia, Tierra del Fuego, and Central Western Argentina in South America, and West Antarctic Rift System volcanism. In contrast, the compositions of marine sediments in the Pacific sector of the Southern Ocean are compatible with mixing of South and North Island NZ dust sources, consistent with NZ’s role as an active dust supplier to the Southern Ocean. New data from Kati Thanda-Lake Eyre in Australia show that it may also be a contributor, if dust from this region is able to reach the Pacific sector independent of other Australian sources.

Distinct chemical and mineralogical composition of Icelandic dust compared to northern African and Asian dust

Abstract. Iceland is a highly active source of natural dust. Icelandic dust has the potential to directly affect the climate via dust–radiation interaction and indirectly via dust–cloud interaction, the snow/ice albedo effect and impacts on biogeochemical cycles. The impacts of Icelandic dust depend on its mineralogical and chemical composition. However, a lack of data has prevented an accurate assessment of the role of Icelandic dust in the Earth system. Here, we collected surface sediment samples from five major Icelandic dust hotspots. Dust aerosols were generated and suspended in atmospheric chambers, and PM10 and PM20 fractions were collected for further analysis. We found that the dust samples primarily consist of amorphous basaltic materials ranging from 8 wt % (from the Hagavatn hotspot) to 60 wt %–90 wt % (other hotspots). Samples had relatively high total Fe content (10 wt %–13 wt %). Sequential extraction of Fe to determine its chemical form shows that dithionite Fe (Fe oxides such as hematite and goethite) and ascorbate Fe (amorphous Fe) contribute respectively 1 %–6 % and 0.3 %–1.4 % to the total Fe in Icelandic dust. The magnetite fraction is 7 %–15 % of total Fe and 1 %–2 wt % of PM10, which is orders of magnitude higher than in mineral dust from northern Africa. Nevertheless, about 80 %–90% of the Fe is contained in pyroxene and amorphous glass. The initial Fe solubility (ammonium acetate extraction at pH 4.7) is from 0.08 % to 0.6 %, which is comparable to low-latitude dust such as that from northern Africa. The Fe solubility at low pH (i.e. pH 2) is significantly higher than typical low-latitude dust (up to 30 % at pH 2 after 72 h). Our results revealed the fundamental differences in composition and mineralogy of Icelandic dust from low-latitude dust. We attribute these differences to the low degree of chemical weathering, the basaltic composition of the parent sediments and glacial processes. Icelandic dust contributes to the atmospheric deposition of soluble Fe and can impact primary productivity in the North Atlantic Ocean. The distinct chemical and mineralogical composition, particularly the high magnetite content (1 wt %–2 wt %), indicates a potentially significant impact of Icelandic dust on the radiation balance in the subpolar and polar regions.

Records of Inorganic Ions and Dust Particles in Snow at Yushugou Glacier No. 6 in the Desert Belt of Northwestern China

Chemical ions and dust particles deposited in snow can be used as indicators of climatic and environmental processes. Understanding their sources, energy transfer and evolutionary mechanisms is extremely important in tracking regional climate and environmental changes. We collected snow samples from three pits at different altitudes and from the surface of Yushugou Glacier No. 6, Tianshan Mountains, China, in the summers of 2017 and 2018. Sea-salt tracing, correlation analysis and factor analysis were used to determine the characteristics and sources of the major ions and mineral dust particles in the snow. We found obvious seasonal variations, with high concentrations of dust particles and major ions deposited during the dust period, and relatively low concentrations deposited during the non-dust period. The concentrations peaked within two distinct dust layers in the snow pits. There was a significant correlation between the peak values and the dust layer. The ionic concentrations were ranked from highest to lowest as Ca2+ > SO42- > Cl- > Na+ > NO3- > NH4+ > Mg2+ > K+. Therefore, SO42- was the dominate anion and Ca2+ was the dominate cation. The major ions in the snow at Yushugou Glacier No. 6 are mainly derived from terrestrial mineral dust but also include limited inputs from human activities and sea salt.