Dust Aerosol Emission Research Articles

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition

Abstract Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dust aerosols are a key source of bio-essential nutrients, can be transported in the atmosphere over large distances, and ultimately deposited onto the ocean's surface, alleviating nutrient limitation and increasing oceanic primary productivity. Currently, the linkages between desertification, dust emissions and ocean fertilization remain poorly understood. Here, we show that dust emitted from Southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected. The conditions required for triggering blooms of this magnitude are anomalous, but current trends in air temperatures, aridity, and dust emissions in Southern Africa suggest that such events could become more probable in the future. Together with the recent findings on ocean fertilization by drought-induced megafires in Australia, our results point toward a potential link between global warming, drought, aerosol emissions, and ocean blooms.

Impact of dust aerosols on the Indian Summer Monsoon Rainfall on intra-seasonal time-scale

The Indian subcontinent is a major hotspot of aerosol loading and several studies have demonstrated the importance of interaction between Asian dust aerosols and the Indian Summer Monsoon Rainfall (ISMR). However, a few studies have suggested a declining trend in the pre-monsoon dust loading over the Indian region. The present study investigates how the decrease in dust emissions influences the intensity of the monsoon rainfall over the Indian region using a fully coupled Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We have conducted two sets of simulation experiments for the June-July-August-September (JJAS) season of 2017: (1) a control experiment with the default dust aerosol emissions, and (2) a sensitivity experiment by reducing dust emissions by 60%. Our analyses show that the reduction in dust emissions significantly alters the spatial distribution of seasonal mean monsoon rainfall with enhanced rainfall over the Bay of Bengal (BoB) and eastern coastal regions, and decreased rainfall over the lower Indo-Gangetic Plain (IGP), and parts of Central India (CI). It is found that the low aerosol loading conditions alter the large-scale circulation patterns along the tropical/sub-tropical region centred between 15°N and 35°N and 40°E −130°E, and through dynamical feedback, strengthens the convective rainfall over the BoB region. As a result, the 10–20 days sub-seasonal mode of the ISMR strengthens, facilitating enhanced westward propagation of rain-bearing systems formed over northern BoB which provides substantial rainfall over vast regions of the Indian subcontinent.

Improvement in Dust Storm Simulation by Considering Stone Coverage Effects for Stony Deserts in East Asia

AbstractApproximately 50% of the Earth's deserts are covered with stony surfaces, not dunes. The stony surfaces often block or diminish mineral dust aerosol emissions through area fraction and roughness element effects. Incorporating these stone coverage effects is crucial for climate and environmental modeling research. Based on our field observations, this study combined the stone coverage effects into a dust simulation model for East Asia using two regression formulas and some constants. The double regression scheme assumed that the stone roughness density could be derived from the coarse fragment fraction of the SoilGrids 2.0 data set. According to the data set, the stone coverage is higher in Western Mongolia and Dzungaria and lower in the Chinese Gobi Desert and the Loess Plateau. Consequently, the model reproduced fewer dust aerosols in the higher coverage areas and more in the lower coverage areas. This simulation result was consistent with the World Meteorological Organization's current weather reports and satellite aerosol observations. The improved model reproduced the diversity of soil erodibility and was well balanced in performance statistics. This study is the first successful investigation of stone coverage effects on dust storm simulation using a realistic stone coverage map to the authors' best knowledge.

A new theoretical model deriving planetary boundary layer height in desert regions and its application on dust devil emissions

Planetary boundary layer height (PBLH) is one of the major factors influencing the occurrence of dust storms and dust devils in desert regions; however, the existing planetary boundary layer parameterization schemes are largely limited to reflect the actual diurnal cycles of PBLH in desert regions, which further affects the global dust-aerosol emission evaluation. A new theoretical model deriving PBLH applicable to the desert areas is developed based on heating effect of dust aerosols and the method calculating PBLH by the vertical profile of virtual potential temperature, and then parameterized by observations at the desert regions in northern China (defined as new PBLH scheme). The results show that the simulated PBLH by the new scheme agrees better with the observations compared to the available PBLH schemes in the WRF model, such as Yonsei University scheme (YSU), Asymmetric Convection Model 2 scheme and Shin-Hong scale–aware scheme. The PBLHs derived from those three schemes might be replaceable by the new scheme due to the great improvement. The normally used YSU scheme and the new PBLH scheme are further applied to evaluate dust-devil emissions, despite the consistent unimodal distribution and similar spatial distribution in daily dust-devil emissions from two schemes in comparison with the measured occurrence frequency of dust devils, the new PBLH scheme improves the emission at the episodes from 09:00 to 18:00 LST (Local Standard Time) with greater magnitude relative to the YSU scheme, and demonstrates more significant differences near the peak-emission time, leading to approximate 1.5 times higher in the summer emission of dust devils. The results imply that the existing schemes underestimate about 5% of the contribution of dust devil emissions to the total amount of dust aerosols, and the new scheme can evaluate better, and provide new insight to understand the impact of the aerosol on climate effect.

Characteristics of dust aerosols and identification of dust sources in Xinjiang, China

Changes in atmospheric particulate matter content directly affect the Earth-atmosphere system balance and climate change and indirectly affect the environment and ecology. Therefore, this matter is receiving increasing attention. A typical arid area with a fragile ecological environment and frequent dust activities, Xinjiang, China, was investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) daily aerosol optical thickness and Ångström wavelength exponent data to obtain the temporal and spatial distribution characteristics of long-term dust aerosols over 20 years. The frequency of occurrence was calculated to accurately identify anthropogenic and natural sources, and data, such as wind speed, were superimposed to quantitatively estimate dust aerosol emissions. The factors that influenced dust aerosol emissions are discussed. The results show that the distribution of dust aerosols in South and North Xinjiang is obviously different, and the average dust aerosol optical depth (DOD) in spring is higher than that in other seasons. The sources of natural dust have little variation and are primarily located in Lop Nur, on the edges of the Taklamakan and Gurbantunggut deserts, in the central Tuha Basin, and in dried-up lakes. The sources of anthropogenic dust are mainly distributed in the farmland areas of the oasis plain and the impact fan plain. Natural dust aerosols are dominant in Xinjiang, with high natural dust emissions in spring. Changes in anthropogenic dust aerosols are caused by production activities, and the annual average anthropogenic dust emissions account for 8% of the total dust emissions. Precipitation can promote a reduction in natural dust emissions. Topography has an obvious effect on the formation and transportation of dust aerosols, which manifests as the frequent occurrence of dust in the basin. The population density data and Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data reveal, that the intensity of human activities has a great impact on anthropogenic dust aerosols. This study provides support for research on how aerosols affect climate and environmental changes in Xinjiang.

Modeled Atmospheric Optical and Thermodynamic Responses to an Exceptional Trans‐Atlantic Dust Outbreak

AbstractLong‐range aerosol transport is an important physical mechanism for ecological, biological, and hydrological elements of the earth system. Regarding the latter, regional climate models have no way of assimilating future aerosol concentrations, so dust aerosol emissions must be parameterized using local landscape and meteorological conditions. The purpose of this study is to evaluate the accuracy of different dust emission settings within the Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) to facilitate future dynamical downscaling work. This study performs nine WRF‐Chem hindcasts, each utilizing a different dust emission configuration, from 1 March to 31 May 2015, coinciding with a Saharan air layer (SAL) dust outbreak during the 2015 Caribbean drought. WRF‐Chem aerosol optical depth (AOD) and Gálvez‐Davison Index (GDI), a convective forecasting parameter, are validated against analogous MODIS, AERONET, and ERA5 products. In aggregate, the GOCART dust emission scheme with Air Force Weather Agency modifications (GOCART‐AFWA) achieved the best balance between AOD and GDI accuracy when employing the default tuning constant (1.00). As the schemes emitted dust more aggressively, WRF‐Chem produced warming at 500 hPa, reducing GDI over the central and eastern Atlantic near the modeled dust trajectory. Though AOD was generally too low over the southwest Atlantic, the eastern Caribbean occupies a transition zone between negative and positive AOD biases where this field was hindcast with relative accuracy. Meanwhile, areas with positive AOD biases were associated with negative GDI biases (and vice versa) indicating the covariability between SAL dust loadings and thermodynamic conditions in the tropical north Atlantic.

Climate characteristics of dust aerosol and its transport in major global dust source regions

In this paper, a 20-year (1991–2010) simulation of dust aerosol emission is conducted by using the global climate model CAM 5.1 (Community Atmosphere Model, version 5.1). The simulation results revealed that North Africa, the Arabian Peninsula and the Middle East, East Asia, Australia, and the other regions respectively account for 60%, 18%, 12%, 2.5% and 7.5% of the global dust aerosol emission. On this basis, the climatology of dust aerosol emission, deposition and transport in the major dust source regions of the world are characterized. The results show that the inter-annual trends of dust emissions and depositions in the four major source areas are basically consistent, and the seasonal variations of dust emissions, dry and wet depositions are stronger than inter-annual variations. The seasonal variations of emissions and total depositions are the strongest in East Asia and the weakest in North Africa. The strongest seasonal variation of wet deposition appears in North Africa and the weakest in Australia. The dry and wet deposition ratios vary significantly with season. East Asia is dominated by wet deposition, while other areas are dominated by dry deposition. The dust transport in four major dust regions is mainly affected by the circulation systems at each level, the free tropospheric (500 hPa) transport of dust aerosol is controlled by the mid-latitude westerlies, and the dust aerosol is predominantly transported from west to east. But, the transport of dust aerosols in the atmospheric boundary layer shows distinct regional characteristics, with weak inter-annual variation and strong seasonal variation.

Contribution of IASI to the Observation of Dust Aerosol Emissions (Morning and Nighttime) Over the Sahara Desert

AbstractObserving the planet at global scale, twice a day, and measuring the whole infrared atmospheric spectrum (8,461 channels at 0.50 cm−1 resolution), Infrared Atmospheric Sounder Interferometer (IASI)/METOP can concurrently detect clouds, determine the 3‐D atmospheric structure (temperature, water vapor, ozone, etc.), surface properties (emissivity and temperature), as well as dust aerosol AOD and altitude. Observing morning (0930 hr) and nighttime (2130 hr), IASI is in relatively good phase with the most frequent times of occurrence of the main Saharan dust uplift mechanisms reported in the literature. Here we classify IASI dust observations according to both the dust loading (AOD) and the dust layer height, providing a more comprehensive picture of dust characteristics. This classification is analyzed at daily scale and its capability to detect dust uplift events is evaluated through comparisons with results from the particularly well documented June 2011 Fennec campaign. Then, a Dust Emission Index (DEI), specific to IASI, is constructed by selecting AOD‐altitude bins with largest AODs and smallest altitudes likely indicative of freshly emitted dust. Applying this to the 12‐year 2007–2018 period, we determine climatological DEI maps and comparisons are made with other equivalent existing results derived from ground‐based or other satellite observations. Results of these comparisons demonstrate the capability of IASI to document the dust distribution over the whole Earth desert areas over a long period of time. The present approach is also suitable to the processing of the at least hourly observations of the coming Infrared Sounder instrument (IRS), planned on board Meteosat Third Generation (2021).

Temporal variation of dust aerosol pollution in northern China

By employing the sandstorm dataset from meteorological station observations, the temporal and spatial variations in dust outbreak duration in the source regions and visibility variations over the downwind regions of northern China were analyzed over the past four decades. The statistics and wind field analyses reveal that after the early 2000s, the duration of dust outbreaks over the potential source areas of northern China had decreased by 63% compared with that in the 1970s, which suggests that the dust aerosol emission intensities in the region were significantly reduced. However, although the potential dust aerosol emission intensities were significantly reduced, the visibility during dust aerosol emission periods increased by only 25%. The emerging potential source areas in the eastern regions, variations in the wind field, increases in up-air winds, and decreases in surface winds all contribute to the observed continued high dust aerosol pollution in northern China since the early 2000s.

Constraining global aerosol emissions using POLDER/PARASOL satellite remote sensing observations

Abstract. We invert global black carbon (BC), organic carbon (OC) and desert dust (DD) aerosol emissions from POLDER/PARASOL spectral aerosol optical depth (AOD) and aerosol absorption optical depth (AAOD) using the GEOS-Chem inverse modeling framework. Our inverse modeling framework uses standard a priori emissions to provide a posteriori emissions that are constrained by POLDER/PARASOL AODs and AAODs. The following global emission values were retrieved for the three aerosol components: 18.4 Tg yr−1 for BC, 109.9 Tg yr−1 for OC and 731.6 Tg yr−1 for DD for the year 2010. These values show a difference of +166.7 %, +184.0 % and −42.4 %, respectively, with respect to the a priori values of emission inventories used in “standard” GEOS-Chem runs. The model simulations using a posteriori emissions (i.e., retrieved emissions) provide values of 0.119 for global mean AOD and 0.0071 for AAOD at 550 nm, which are +13.3 % and +82.1 %, respectively, higher than the AOD and AAOD obtained using the a priori values of emissions. Additionally, the a posteriori model simulation of AOD, AAOD, single scattering albedo, Ångström exponent and absorption Ångström exponent show better agreement with independent AERONET, MODIS and OMI measurements than the a priori simulation. Thus, this study suggests that using satellite-constrained global aerosol emissions in aerosol transport models can improve the accuracy of simulated global aerosol properties.

Large Effects of Particle Size Heterogeneity on Dynamic Saltation Threshold

Reliably predicting the geomorphology and climate of planetary bodies requires knowledge of the dynamic threshold wind shear velocity below which saltation transport ceases. Here we measure this threshold in a wind tunnel for four well‐sorted and two poorly sorted sand beds by visual means and by a method that exploits a regime shift in the behavior of the surface roughness caused by momentum transfer from the wind to the saltating particles. For our poorly sorted sands, we find that these measurement methods yield different threshold values because, at the smaller visual threshold, relatively coarse particles do not participate in saltation. We further find that both methods yield threshold values that are much larger (60–250%) for our poorly sorted sands than for our well‐sorted sands with similar median particle diameter. In particular, even a rescaling of the dynamic saltation threshold based on the 90th percentile particle diameter rather than the median diameter cannot fully capture this difference, suggesting that relatively very coarse particles have a considerable control on the dynamic threshold. Similar findings were previously reported for water‐driven sediment transport. Our findings have important implications for quantitative predictions of saltation transport‐related geophysical processes, such as dust aerosol emission.

Size‐Independent Susceptibility to Transport in Aeolian Saltation

AbstractNatural wind‐eroded soils contain a mixture of particle sizes. However, models for aeolian saltation are typically derived for sediment bed surfaces containing only a single particle size. To nonetheless treat natural mixed beds, models for saltation and associated dust aerosol emission have typically simplified aeolian transport either as a series of noninteracting single particle size beds or as a bed containing only the median or mean particle size. Here we test these common assumptions underpinning aeolian transport models using measurements of size‐resolved saltation fluxes at three natural field sites. We find that a wide range of sand size classes experience “equal susceptibility” to saltation at a single common threshold wind shear stress, contrary to the “selective susceptibility” expected for treatment of a mixed bed as multiple single particle size beds. Our observation of equal susceptibility refutes the common simplification of saltation as a series of noninteracting single particle sizes. Sand transport and dust emission models that use this incorrect assumption can be both simplified and improved by instead using a single particle size representative of the mixed bed.

The global aerosol–climate model ECHAM6.3–HAM2.3 – Part 1: Aerosol evaluation

Abstract. We introduce and evaluate aerosol simulations with the global aerosol–climate model ECHAM6.3–HAM2.3, which is the aerosol component of the fully coupled aerosol–chemistry–climate model ECHAM–HAMMOZ. Both the host atmospheric climate model ECHAM6.3 and the aerosol model HAM2.3 were updated from previous versions. The updated version of the HAM aerosol model contains improved parameterizations of aerosol processes such as cloud activation, as well as updated emission fields for anthropogenic aerosol species and modifications in the online computation of sea salt and mineral dust aerosol emissions. Aerosol results from nudged and free-running simulations for the 10-year period 2003 to 2012 are compared to various measurements of aerosol properties. While there are regional deviations between the model and observations, the model performs well overall in terms of aerosol optical thickness, but may underestimate coarse-mode aerosol concentrations to some extent so that the modeled particles are smaller than indicated by the observations. Sulfate aerosol measurements in the US and Europe are reproduced well by the model, while carbonaceous aerosol species are biased low. Both mineral dust and sea salt aerosol concentrations are improved compared to previous versions of ECHAM–HAM. The evaluation of the simulated aerosol distributions serves as a basis for the suitability of the model for simulating aerosol–climate interactions in a changing climate.

Retrieval of desert dust and carbonaceous aerosol emissions over Africa from POLDER/PARASOL products generated by the GRASP algorithm

Abstract. Understanding the role atmospheric aerosols play in the Earth–atmosphere system is limited by uncertainties in the knowledge of their distribution, composition and sources. In this paper, we use the GEOS-Chem based inverse modelling framework for retrieving desert dust (DD), black carbon (BC) and organic carbon (OC) aerosol emissions simultaneously. Aerosol optical depth (AOD) and aerosol absorption optical depth (AAOD) retrieved from the multi-angular and polarimetric POLDER/PARASOL measurements generated by the GRASP algorithm (hereafter PARASOL/GRASP) have been assimilated. First, the inversion framework is validated in a series of numerical tests conducted with synthetic PARASOL-like data. These tests show that the framework allows for retrieval of the distribution and strength of aerosol emissions. The uncertainty of retrieved daily emissions in error free conditions is below 25.8 % for DD, 5.9 % for BC and 26.9 % for OC. In addition, the BC emission retrieval is sensitive to BC refractive index, which could produce an additional factor of 1.8 differences for total BC emissions. The approach is then applied to 1 year (December 2007 to November 2008) of data over the African and Arabian Peninsula region using PARASOL/GRASP spectral AOD and AAOD at six wavelengths (443, 490, 565, 670, 865 and 1020 nm). Analysis of the resulting retrieved emissions indicates 1.8 times overestimation of the prior DD online mobilization and entrainment model. For total BC and OC, the retrieved emissions show a significant increase of 209.9 %–271.8 % in comparison to the prior carbonaceous aerosol emissions. The model posterior simulation with retrieved emissions shows good agreement with both the AOD and AAOD PARASOL/GRASP products used in the inversion. The fidelity of the results is evaluated by comparison of posterior simulations with measurements from AERONET that are completely independent measurements and more temporally frequent than PARASOL observations. To further test the robustness of our posterior emissions constrained using PARASOL/GRASP, the posterior emissions are implemented in the GEOS-5/GOCART model and the consistency of simulated AOD and AAOD with other independent measurements (MODIS and OMI) demonstrates promise in applying this database for modelling studies.

Projected changes in dust emissions and regional air quality due to the shrinking Salton Sea

Abstract The Salton Sea lake level in California is expected to transition in 2018 from a period of gradual decline to a new era of rapid decline that will expose about 40% of the year 2000 lakebed to wind erosion by 2030. The newly exposed Playa substrate can emit large amounts of particulate matter (PM) and thus degrade regional air quality. We use the Weather Research Forecast model (WRF-Chem) to estimate changes in dust aerosol emission and distribution in the Salton Sea region from 2000 to 2030. First, we evaluate simulations of present day wind speed, mineral dust emission, concentration, and optical depth over the region. WRF-Chem at 4 km spatial resolution satisfactorily reproduces the present-day spatio-temporal pattern of dust emission. With an estimated 38% exposure of the Salton Sea by 2030, the domain-averaged PM10 in the 2 × 2 degree domain enclosing the Sea increases on average by 11% and by nearly a factor of ten in localized source areas. The simulated increases in dust emission are consistent with earlier empirical estimates although our estimates are comparatively lower. Our regional model provides more spatially detailed and quantitative attribution of the projected air quality degradation. For example, our model suggests that newly exposed playa emissions will emanate more from the southwest than southeast side of the lake, even though most of the new playa will be on the southeast side. These results may inform decisions that affect trade-offs between environmental quality, human health, and water-use issues in the Salton Sea region.

Detection of IASI dust AOD trends over Sahara: How many years of data required?

Detecting trends in climate variables has become of great importance in the context of the rapid evolution of the Earth's climate. Among the climate variables recognized as acting on climate variability, aerosols continue to contribute one of the largest uncertainties to the total radiative forcing estimate. The present study focuses on dust aerosols, a major contributor to total aerosol loading. Observation from space offers a good opportunity to follow aerosol evolution at global scale and over long time series. In this context, infrared observations, by allowing retrieving dust optical depth (AOD) day-time and night-time, over oceans and over continents, in particular over desert, is complementary to observations in the visible on which a majority of aerosol studies are so far based. The two spectral domains are not sensitive to the same range of particle size, coarse mode particles (>1 μm) being preferentially observed in the infrared, when both coarse and fine mode particles (0.1–1 μm) are observed in the visible making the distinction between the two modes difficult. Starting from METOP-A/IASI-derived dust AOD (July 2007 to June 2017), this study aims at detecting and estimating, day-time and night-time, dust AOD trends over Sahara, a region where dust aerosol emissions are frequent and often intense. Detecting trends in geophysical variable time series is a difficult task due to the frequent presence of serial correlation, to holes in the data, to “outliers”, or to variables not normally distributed, etc. Here, trends are determined using the non-parametric Theil-Sen slope estimator followed by the Mann-Kendall statistical test for randomness against trend, the statistical hypothesis (H0) being that the trend is equal to zero. Resulting trends are judged to be significantly different from zero if their so-called “confidence level” is above a given percentage, usually 95% (referred to as “real” trend in the following). Then, in a second step, supposing the statistical hypothesis is now that a non-zero trend of specified magnitude exists, we can calculate the probability that this hypothesis is true. The number of years of data required to detect a “real” trend of a specified magnitude with probability 0.9 (“probability-assigned real” trend) is finally determined following (Tiao et al., 1990). This approach is then applied to the 120 months of IASI-retrieved dust AOD. Main conclusions are that the present 10-year period of IASI observations is still too limited to provide enough reliable, probability-assigned, trends over Sahara and that a period of 14–15 years would largely increase their number and spatial coverage. This is fully compatible with the already planned length of the IASI series on board METOP-A to C, taking into account the high demonstrated stability of this instrument.

Modern dust aerosol availability in northwestern China

The sources of modern dust aerosols and their emission magnitudes are fundamental for linking dust with climate and environment. Using field sample data, wind tunnel experiments and statistical analysis, we determined the contributions of wadis, gobi (stony desert), lakebeds, riverbeds, and interdunes to modern dust aerosol availability in the three important potential dust sources including the Tarim Basin, Qaidam Basin, and Ala Shan Plateau of China. The results show that riverbeds are the dominant landscape for modern dust aerosol availabilities in the Qaidam Basin, while wadis, gobi, and interdunes are the main landscapes over the Ala Shan Plateau and Tarim Basin. The Ala Shan Plateau and Tarim Basin are potential dust sources in northwestern China, while the Qaidam Basin is not a major source of the modern dust aerosols nowadays, and it is not acting in a significant way to the Loess Plateau presently. Moreover, most of modern dust aerosol emissions from China originated from aeolian processes with low intensities rather than from major dust events.

Dust aerosol emission over the Sahara during summertime from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations

Dust aerosols are an important component of the climate system and a challenge to incorporate into weather and climate models. Information on the location and magnitude of dust emission remains a key information gap to inform model development. Inadequate surface observations ensure that satellite data remain the primary source of this information over extensive and remote desert regions. Here, we develop estimates of the relative magnitude of active dust emission over the Sahara desert based on data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Utilising the unique vertical profile of aerosol characteristics provided by CALIOP our algorithm identifies emission from aerosol extinction and lidar backscatter in the near surface layers. From the long-term CALIOP archive of day and night-time orbits over 2006–13 we construct coarse resolution maps of a new dust emission index (DEI) for the Sahara desert during the peak summer dust season (June to September). The spatial structure of DEI indicates highest emission over a broad zone focused on the border regions of Southern Algeria, Northern Mali and northwest Niger, displaced substantially (∼7°) to the east of the mean maximum in satellite-derived aerosol optical depth. In this region night-time emission exceeds that during the day. The DEI maps substantially corroborate recently derived dust source frequency count maps based on back-tracking plumes in high temporal resolution SEVIRI imagery. As such, a convergence of evidence from multiple satellite data sources using independent methods provides an increasingly robust picture of Saharan dust emission sources. Various caveats are considered. As such, quantitative estimates of dust emission may require a synergistic combined multi-sensor analysis.

The importance of Harmattan surges for the emission of North African dust aerosol

AbstractDust aerosol is important in the Earth system, but the relative impact of meteorological mechanisms on North African dust emission remains unclear. This study presents the first climatology of dust emission amounts associated with Harmattan surges (HSs), characterized by postfrontal strengthening of near‐surface winds. A new automated identification uses their strong isallobaric winds as an indicator for HSs in 32 years of ERA‐Interim reanalysis. Their impact on dust aerosol emission is estimated by combining the identified events with derived dust emissions. The estimate highlights that about one third of the total emission mass is associated with HSs. Spring shows the largest associated emissions of 30–50% of the monthly totals consistent with the largest number and duration of HSs. Regional emission contributions of up to 80% in the north coincide with the overall largest emission maxima in spring. The importance of HSs for dust emission implies that aerosol‐climate models need to accurately represent synoptic‐scale storms.

Fluorine concentration in snow cover within the impact area of aluminium production plant (Krasnoyarsk city) and coal and gas-fired power plant (Tomsk city)

The fluorine contents in snow melt water find in the impact areas of aluminum production plant and coal and gas-fired power plant are compared. In melt water, soluble fluoride is found in the form of fluoride ion, the content of which was determined by the potentiometric method using ion-selective electrode. According to the measurements of 2013-2014, fluoride content in melt water ranges 10.6-15.4 mg/dm3 at the distance 1-3 km from the borders of Krasnoyarsk aluminum plant with the mean value 13.1 mg/dm3. Four-year monitoring from 2012 to 2015 in the impact area of Tomsk coal and gas-fired power plant showed that fluoride content in melt water in vicinity of the thermal power plant is significantly lower than in the samples from the impact area of the aluminum plant. But higher content of fluoride ion (0.2 - 0.3 mg/dm3) in snow samples in vicinity of coal and gas-fired power plant was revealed in winter of 2015. Intake of soluble fluoride is mostly explained by dust-aerosol emissions of study plants and deposition of fluorine compounds from air.