African Dust Research Articles

Climate Change, Air Pollution, African Dust Impacts on Public Health and Sustainability in Europe

Abstract Climate change poses a significant threat to environmental sustainability and public health, leading to extreme weather events, rising sea levels, and biodiversity loss. Research on air pollution from African dust adversely associated with climate change highlights its significant role in trapping heat in the atmosphere and causing heat-related illnesses, cardiovascular disorders, and respiratory ailments. Smog, dust, acid rain, and ozone depletion also negatively impact ecosystems. The methods of the study also include the dynamics of climate change-induced air pollution. The implications for public health and environmental sustainability through GWR modeling and MODIS-NDVI analysis of controlling air pollution are crucial for reducing the climate crisis, safeguarding public health, and maintaining ecosystem sustainability. Results from particulate matter (PM 2.5-10), which consists of tiny particles with varying diameters, can enter the respiratory system through inhalation. This can lead to a diameter of less than 10 μm (PM 2.5-10). According to the relevant legislation, the limit value refers to the daily average value and must not exceed 50 μg/m3. While ozone in the stratosphere serves a protective function against ultraviolet radiation, excessive levels at ground level can be harmful and have been recorded in atmospheric samples ranging from 146.6 μg/m3 up to 702.3 μg/m3. impacting the respiratory and cardiovascular systems. Policy leaders, businesses, and individuals need to be proactive in reducing air pollution, adopting clean energy technology, and implementing stricter pollution rules. Stricter pollution rules, environmentally friendly transportation choices, and the adoption of clean energy technology. The sustainability of the ecosystem and public health are significantly impacted by climate change linked to air pollution. To solve these global problems and move toward a healthier, cleaner future for future generations, we must act now on climate justice. Key messages • Examine the impact of African dust air pollution on public health and its significant impacts from climate change, provide solutions to mitigate its effects on environmental sustainability in Europe. • Public health workers, Policymakers and stakeholders must prioritize reducing emissions and enforcing strict air quality laws to mitigate the negative impact of African dust on European populations.

African dust: Occurrence, health consequences, and impacts on Texas

The drylands of North Africa (Sahara and Sahel) are the world’s largest sources of airborne dust. Clouds of African dust aerosols have been long known to be blown westwards across the Atlantic, and by the 1990s were recognized to be transported across and over Texas. African dust incursions in Texas typically happen several times per year in late spring and summer, manifesting as hazy skies overhead and increased ground-level concentrations of PM2.5 (particulate matter fine enough to be inhaled into the human lower respiratory tract). African dust exposure has many reported human health effects in Europe and the Caribbean, including increased all-cause mortality and increased respiratory and cardiovascular disease morbidity and mortality. In Texas, African dust’s greatest impacts occur in the Houston metropolitan area where it has been quantitatively shown to increase ambient aerosol concentrations. The potential of African dust increasing concentrations of inhalable particulate matter beyond regulatory limits is of concern. A sequence of investigations filtering particles from the air, measuring their concentrations, and subjecting them to elemental analysis documented far-transported African dust’s role in air quality in Houston and Galveston. African dust’s contributions to air pollution have been separated from those of local soils and industrial emissions, and Saharan-Sahelian dust has been indicated to sometimes constitute the majority of PM2.5 mass in Houston. While studies show the presence of inhalable metals and microorganisms including opportunistic pathogens during Saharan air incursions in Houston, the human health effects of African dust in Texas remain yet unspecified and merit further investigation. Keywords: aerosols; Africa, Northern; air pollution; dust; particulate matter; public health; Texas

Long-range transport of air pollutants increases the concentration of hazardous components of PM2.5 in northern South America

Abstract. Long-range transport (LRT) of air pollutants from a range of sources can substantially enhance background pollution levels, especially in urbanized regions, which can exacerbate high-pollution episodes. In the Aburrá Valley (AV), Colombia, and other cities in northern South America, biomass burning (BB), dust, and volcanic degassing have been identified as sources of long-range aerosol transport. However, the impact of these sources on air quality and the characterization of these sources have yet to be thoroughly studied. This work investigates the influence of these sources on the chemical composition of PM2.5 during annual and intra-annual high-load aerosol events in the AV. We identified, tracked, and meteorologically characterized LRT events and evaluated their influence on PM2.5 concentration and chemical composition. We found that the LRT of aerosols from BB, dust, and volcanic degassing influenced approximately 13 %, 8 %, and 13 % of days in the year, respectively. We applied the positive-matrix-factorization (PMF) statistical model to quantify PM2.5 concentrations and chemical compositions for the different LRT event types (e.g., BB). For BB events, we identified large contributions from organic carbon (OC1 and OC2), F−, and secondary aerosol tracers (SO42- and NO3-). For dust LRT events, crustal mineral components, along with Ti and Ca, were the primary contributors to aerosol composition, while SO42-, Na, Al, and Ca were the primary contributors during volcanic events. The concentrations of some ions and toxic heavy metals (Cr, Mn, Cd, and Ni) were also elevated during BB and volcanic-degassing events. BB contributed the most to PM2.5 levels during the LRT events (∼11 µg m−3), while contributions from aerosols arising from dust and volcanic events were also substantial (<7 µg m−3). Our study identifies the Orinoco and the Middle Magdalena Valley as sizable sources of BB aerosols and Nevado del Ruiz as a source of volcanic aerosols. Additionally, we found that African dust reached the Andean region via the Caribbean route. As a result, we identify the need for future chemical-transport modeling studies in the region and new support strategies to manage internal and external pollution sources that degrade air quality in the AV and the surrounding region.

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.

Increased rupture of cypress pollen type due to atmospheric water in central and southeastern Spain

This study aims to investigate the meteorological variables determining Cupressaceae pollen grain disruption in the environment. A parallel sampling of pollen grains and disrupted Cupressaceae pollen grains was performed in six cities using two Spanish aerobiological networks. The pollen concentrations, disrupted pollen concentrations, percentage of disrupted pollen and number of days when the percentage of disrupted pollen was above or equal to 50 % were quantified during two pollen seasons. The concentrations were determined following the standardised method EN 16868. Results show that the concentrations of pollen grains and disrupted pollen grains were not determined by geographical features and rarely by bioclimatic variables or indexes but by the ornamental use of the specimens in the vicinity of the pollen sampler, highlighting the possibility of using management practices to reduce exposure to allergens in the cities. African dust outbreaks coincided with higher concentrations of pollen grains and disrupted pollen grains, but the reduced percentage of disrupted pollen grains pointed to a non-causal relationship with long-distance transport. The effect of wind and maximum gusts remained negligible. The triggering factor for pollen disruption was the amount of water in the atmosphere, mainly reported as relative humidity. Rainfall increased the effect of disruption due to pollen grain swelling caused by its wash-out effect. The higher the relative humidity, the higher the disrupted pollen concentrations. This aligns with the mechanism of Cupressaceae reproduction since the family needs a water medium in the form of pollination droplets for the pollination tube to develop and the pollen grain to perform its biological function. Therefore, people that develop allergic symptoms to Cupresaceae pollen should avoid exposure during days with high relative humidity in the main pollen season.

The emission, transport, and impacts of the extreme Saharan dust storm of 2015

Abstract. ​​​​​​​Each summer, the Saharan Air Layer (SAL) transports massive amounts of mineral dust across the Atlantic Ocean, affecting weather, climate, and public health over large areas. Despite the considerable impacts of African dust, the causes and impacts of extreme trans-Atlantic African dust events are not fully understood. The “Godzilla” trans-Atlantic dust event of 2020 has been extensively studied, but little is known about other similar events. Here, we examine the June 2015 event, the second strongest trans-Atlantic African dust event that occurred during the summers from 2003–2022. This event was characterized by moderately high dust emissions over western North Africa and an extremely high aerosol optical depth (AOD) over the tropical North Atlantic. The high dust loading over the Atlantic is associated with atmospheric circulation extremes similar to the Godzilla event. Both the African easterly jet (AEJ) and Caribbean low-level jet (CLLJ) have greatly intensified, along with a westward extension of the North Atlantic subtropical high (NASH), all of which favor the westward transport of African dust. The enhanced dust emissions are related to anomalously strong surface winds in dust source regions and reduced vegetation density and soil moisture across the northern Sahel. The dust plume reduced net surface shortwave radiation over the eastern tropical North Atlantic by about 25 W m−2 but increased net longwave flux by about 3 W m−2. In contrast to the Godzilla event, the 2015 event had minor air quality impacts on the US, partially due to the extremely intensified CLLJ that dispersed the dust plume towards the Pacific.

Paleoclimate Controls on West African Dust Inferred from Rb/Sr and Si/Al of Sediments in an Eastern Equatorial Atlantic Marine Core

Increased dust emissions from dryland areas and their effects on human health, ecosystem viability, and environmental change are a global concern in the face of the growing climate crisis. Dust plume emissions from the West African landmass, Sahara, and Sahel areas comprise a major fraction of the global aerosol budget. Dust plume intensity is closely related to regional winds (e.g., Harmattan, Sahara Air Layer), the Intertropical Convergence Zone, monsoonal seasonality, marine currents, and physiography. To study terrigenous material emitted from the continent over the last ~260 kyr (late Quaternary), we used X-ray fluorescence spectroscopy (XRF) to analyze a ~755 cm long marine sediment core from the eastern equatorial Atlantic Ocean, resulting in nearly 1400 discrete measurements. Spectral analysis results suggest that concentrations of elements (Rb, Sr, Si, Al) preserved in the sediments are correlated to different types of orbital climate forcing. Chemical weathering intensity indicated by the Rb/Sr ratio was sensitive to seasonal insolation variations controlled by precession cycles (23–18 kyr), which presumably reflects the relationship between monsoonal rainfall and sensible heating of the continent. Spectral analysis of silicate mineral grain size (Si/Al) showed significant 40 kyr cycles that were paced by obliquity. Based on these data, we infer that winter tradewind activity accelerated in response to the intertropical insolation gradient induced by high obliquity. High Rb/Sr ratios during the last glacial maximum and penultimate glacial maximum may have been due to a predominance of mechanical weathering over chemical weathering under dry/cool climates or the dissolution of Sr-bearing carbonates by corrosive glacial bottom waters.

Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic in Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions.

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect biogeochemical cycles, yet their global cycles are poorly understood. Here, we examined trends in 21 years of aerosol measurements made at Ragged Point, Barbados, the easternmost promontory on the island located in the eastern Caribbean Basin. Though the site has historically been used to characterize African dust transport, here we focused on changes in nitrate and non-sea-salt (nss) sulfate aerosols from 1990-2011. Nitrate aerosol concentrations averaged over the entire period were stable at 0.59 μg m-3 ± 0.04 μg m-3, except for elevated nitrate concentrations in the spring of 2010 and during the summer and fall of 2008 due to the transport of biomass burning emissions from both northern and southern Africa to our site. In contrast, from 1990 to 2000, nss-sulfate decreased 30% at a rate of 0.023 μg m-3 yr-1, a trend which we attribute to air quality policies enacted in the United States (US) and Europe. From 2000-2011, sulfate gradually increased at a rate of 0.021 μg m-3 yr-1 to pre-1990s levels of 0.90 μg m-3. We used the Community Multiscale Air Quality (CMAQ) model simulations from the EPA's Air QUAlity TimE Series (EQUATES) to better understand the changes in nss-sulfate after 2000. The model simulations estimate that increases in anthropogenic emissions from Africa explain the increase in nss-sulfate observed in Barbados. Our results highlight the need to better constrain emissions from developing countries and to assess their impact on aerosol burdens in remote source regions.

Quantification of Contributions from Different Dust Sources to the Distribution and the Variation of Spring Dust over the Tibetan Plateau and Corresponding Mechanisms since 2000

Abstract Dust is the predominant type of aerosol over the Tibetan Plateau (TP) due to the existence of surrounding significant dust sources. However, the contributions of different dust sources to the distribution and variation of dust over the TP and corresponding mechanisms are still being explored. By separating emissions from different dust sources in a numerical model, this study detected that dust originating from East Asia, the Middle East, and North Africa are the main contributors to spring dust over the TP, accounting for 42%–68%, 13%–27%, and 9%–25% of the total dust concentration, respectively. East Asian dust primarily affects the dust over the central and northern parts of the TP, whereas Middle Eastern and North African dust mainly contributes to the dust over the western and southern parts of the TP. Additionally, the variation in dust over the TP is related to East Asian and North African dust, which contribute 58% and 35% of the total variation, respectively. The mechanism underlying this association is attributable to the SST over the northern North Atlantic and updrafts over the northern slope of the TP: the increased SST enhances westerlies from North Africa to East Asia and northwesterly winds over the northern slope of the TP and combines with the stronger westerlies to promote the transport of East Asian and North African dust to the TP. Consequently, it is necessary to focus on the impact of multiple dust sources on the dust over the TP.

Application of aggregation operators for forecasting [formula omitted] fluctuations: From available Caribbean data sites to unequipped ones

Air pollution is a substantial issue for public health. Predicting the levels of airborne particles, especially those originating from natural phenomena like sand mists from the African dust belt, enables more effective warnings for affected populations. Currently, there are only three islands that continuously measure PM10 concentrations in the Caribbean area. Thus, there is a main issue for the forecast of these particulate pollutants for unequipped sites. In this article, a new approach based on the use of aggregation operators in a non-fuzzy framework allows to predict the quantity of PM10 for certain sites in this geographical area. It is the characteristics of non-linearity and downward reinforcement of the fuzzy operators used (triple Pi and t-norms) which make it possible to model the evolution of a phenomenon as complex as the sand mists from African dust belt. The time series having been normalized, the tests were carried out on two of the three sites (Martinique and Guadeloupe) to predict the values of the third site (Puerto Rico) and assess the quality of the prediction. The mean absolute error (MAE), the mean bias error (MBE), the root mean square error (RMSE) and the index of agreement (IOA) values show that this approach provides significant results. The African dust seasonality strongly impacts these performances metrics. These initial promising findings emphasize that the utilization of aggregation operators is a robust method for forecasting PM10 fluctuations, eliminating the need for complex parameterization or learning phase that would otherwise entail significant computational costs.

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

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

Estimating the probability of occurrence of African dust outbreaks over regions of the western Mediterranean basin from thermodynamic atmospheric parameters

Desert dust is currently recognized as a health risk factor. Therefore, the World Health Organization (WHO) is actively promoting the establishment of early warning systems for sand and dust storms. This study introduces a methodology to estimate the probability of African dust outbreaks occurring in eight different regions of the Iberian Peninsula and the Balearic Islands. In each region, a multilinear regression model was developed to calculate daily probabilities of dust events using three thermodynamic variables (geopotential thickness in the 1000–500 hPa layer, mean potential temperature between 925 and 700 hPa, and temperature anomalies at 850 hPa) as assessment parameters. All days with African dust transport over each study region were identified in the period 2001–2021 using a proven procedure. This information was then utilized to establish a functional relationship between the values of the thermodynamic parameters and the probability of African dust outbreaks occurring. The validation of this methodology involved comparing the daily probabilities of dust events generated by the models in 2001–2021 with the daily African dust contributions to PM10 regional background levels in each region. On average, daily dust contributions increased proportionally with the increase in daily probabilities, reaching zero for days with low probabilities. Furthermore, a well-defined seasonal evolution of probability values was observed in all regions, with the highest values in the summer months and the lowest in the winter period, ensuring the physical relevance of the models' results. Finally, upward trends were observed in all regions for the three thermodynamic parameters over 1940–2021. Thus, the probability of dust events development also increased in this period. It demonstrates that the aggravation of warm conditions in southern Europe in the last decades, have modified the frequency of North-African dust outbreaks over the western Mediterranean basin.

“Seeing” Beneath the Clouds—Machine‐Learning‐Based Reconstruction of North African Dust Plumes

AbstractMineral dust is one of the most abundant atmospheric aerosol species and has various far‐reaching effects on the climate system and adverse impacts on air quality. Satellite observations can provide spatio‐temporal information on dust emission and transport pathways. However, satellite observations of dust plumes are frequently obscured by clouds. We use a method based on established, machine‐learning‐based image in‐painting techniques to restore the spatial extent of dust plumes for the first time. We train an artificial neural net (ANN) on modern reanalysis data paired with satellite‐derived cloud masks. The trained ANN is applied to cloud‐masked, gray‐scaled images, which were derived from false color images indicating elevated dust plumes in bright magenta. The images were obtained from the Spinning Enhanced Visible and Infrared Imager instrument onboard the Meteosat Second Generation satellite. We find up to 15% of summertime observations in West Africa and 10% of summertime observations in Nubia by satellite images miss dust plumes due to cloud cover. We use the new dust‐plume data to demonstrate a novel approach for validating spatial patterns of the operational forecasts provided by the World Meteorological Organization Dust Regional Center in Barcelona. The comparison elucidates often similar dust plume patterns in the forecasts and the satellite‐based reconstruction, but once trained, the reconstruction is computationally inexpensive. Our proposed reconstruction provides a new opportunity for validating dust aerosol transport in numerical weather models and Earth system models. It can be adapted to other aerosol species and trace gases.

Effect of Saharan dust episodes on the accuracy of photovoltaic energy production forecast in Hungary (Central Europe)

In order to meet global sustainability goals, in particular, the rapid decarbonisation of the energy sector in combination with geopolitical energy security issues, as well as further improvement in regional air quality-the so-called renewable energy sources are becoming increasingly critical and important. Photovoltaic power (PV) generation is clearly the most widely deployed (non-hydro) renewable energy source globally, which still has a significant growth potential in many countries, including Hungary.However, due to the intermittent nature and the strong dependency of photovoltaic power production on meteorological factors, continuous adjustment of electric power in the electric grid is needed. This, in turn, requires the most accurate forecast of the photovoltaic energy to be produced in the ultra-short term (15 min) and short term (1 day) in order to minimise last-minute and high-price energy acquisition or unplanned kicks-in of gas-fired auxiliary power plants.In this paper, we evaluate the impacts of large-scale dust transport episodes on the accuracy of forecasts of PV power generation. The numbers and intensities of Saharan dust storm events reaching Central Europe have increased over the last decade, hitting a new record in 2022 with 16 (!) African dust episodes observed over Hungary. We have shown that the semi-direct effect of atmospheric dust particles on high-level cloud formation rather than their direct irradiance-reducing effect is responsible for the reduced accuracies of e short-term (24-h) PV energy production forecasts during these events.

Late Holocene Dust Deposition Fluxes Over the Entire South Atlantic Ocean

AbstractMineral dust accumulated on the ocean floor is an important archive for reconstructing past atmospheric circulation changes and climatological conditions in the source areas. Dust emitted from Southern Hemisphere dust sources is widely deposited over the oceans. However, there are few records of dust deposition over the open ocean, and a large need for extended geographical coverage exists. We present a large data set (134 surface sediment samples) of Late Holocene dust deposition from seafloor surface sediments covering the entire South Atlantic Ocean. Polymodal grain‐size distributions of the lithogenic fraction indicate that the sediments are composed of multiple sediment components. By using end‐member modeling, we attempt to disentangle the dust signal from non‐aeolian sediments. Combined with 230Th‐normalized lithogenic fluxes, we quantified the specific deposition fluxes for mineral dust, crrent‐sorted sediments and ice‐rafted debris (IRD). Although the method could not completely separate the different components in every region, it shows that dust deposition off the most prominent dust source for the South Atlantic Ocean—southern South America—amounts up to approximately 0.7 g cm−2 Kyr−1 and decreases downwind. Bottom‐current‐sorted sediments and IRD are mostly concentrated around the continental margins. The ratio of the coarse to fine dust end members reveals input from north African dust sources to the South Atlantic. The majority of the observations are in good agreement with new model simulations. This extensive and relevant data set of dust grain size and deposition fluxes to the South Atlantic could be used to calibrate and validate further model simulations.

Wildfire and African dust aerosol oxidative potential, exposure and dose in the human respiratory tract

Exposure to wildfire smoke and dust can severely affect air quality and health. Although particulate matter (PM) levels and exposure are well-established metrics linking to health outcomes, they do not consider differences in particle toxicity or deposition location in the respiratory tract (RT). Usage of the oxidative potential (OP) exposure may further shape our understanding on how different pollution events impact health. Towards this goal, we estimate the aerosol deposition rates, OP and resulting OP deposition rates in the RT for a typical adult Caucasian male residing in Athens, Greece. We focus on a period when African dust (1–3 of August 2021) and severe wildfires at the northern part of the Attika peninsula and the Evia island, Greece (4–18 of August 2021) affected air quality in Athens. During these periods, the aerosol levels increased twofold leading to exceedances of the World Health Organization (WHO) [15(5) μg m−3] PM10 (PM2.5) air quality standard by almost 100 %. We show that the OP exposure is 1.5-times larger during the wildfire smoke events than during the dust intrusion, even if the latter was present in higher mass loads – because wildfire smoke has a higher specific OP than dust. This result carries two important implications: OP exposure should be synergistically used with other metrics - such as PM levels - to efficiently link aerosol exposure with the resulting health effects, and, certain sources of air pollution (in our case, exposure to biomass burning smoke) may need to be preferentially controlled, whenever possible, owing to their disproportionate contribution to OP exposure and ability to penetrate deeper into the human RT.

20 years of columnar aerosol properties at Valencia area (Eastern Spain) by ground-based sun-photometry

In this paper, a climatological study focused on the analysis of atmospheric aerosols properties over Burjassot and Aras de los Olmos AERONET sites, located at Eastern Spain, is performed. Computed mean values for Aerosol Optical Depth (AOD440), Ångström exponent (α440−870) and columnar water vapor (w) in Burjassot (Aras de los Olmos) are 0.19±0.08 (0.10±0.02), 1.21±0.16 (1.18±0.25) and 1.87±0.68cm (0.94±0.10cm), respectively. From the monthly statistics of w and AOD, it is concluded that summer months are characterised by higher humidity and turbidity, being the latter favoured by particle stagnation, recirculation, secondary aerosol formation, hygroscopic processes and North African dust intrusions. Regarding the volume size distribution, well developed fine and coarse modes are found in summer. On the other hand, the spectral dependence of the asymmetry parameter (g) describes a decrease in λ up to 870nm, and then a slight increase due to the influence of dust particles. The computed mean values for the asymmetry parameter (g440) are 0.700±0.013 (0.709±0.016) for Burjassot (Aras de los Olmos). With respect to the Single Scattering Albedo (SSA) and the complex refractive index, an additional analysis using Level 1.5 data is performed, as relatively few data points pass the filters imposed by the Level 2.0 conditions. In the case of SSA, which is found to be larger in spring and summer months, the obtained mean annual values at 440nm are 0.94±0.03 (0.95±0.03) for Burjassot (Aras de los Olmos). Finally, regarding the complex refractive index, the mean values of the real part (m440) are 1.50±0.03 (1.49±0.03), and for the imaginary part (∣k440∣) are 0.007±0.004 (0.004±0.003) in Burjassot (Aras de los Olmos). The present study is complemented with three analyses based on the distinction between the different aerosol types. To begin with, these are classified according to their nature, being the most abundant continental clean aerosols. Next, Gobbi diagrams are plotted for both sites, depicting a clustered region of coarse aerosols, as well as particle growth traces. Finally, the different air masses affecting the measurement sites are studied, reaching to the conclusion that these originated in the European and the African continents are the most turbid ones. To conclude this study, a seasonal Mann-Kendall test is applied to AOD, α, w and SSA measurements in order to study possible trends. Hence, a statistically significant (>80%) decreasing trend in AOD is observed for most months; whereas α, w and SSA do not show statistically significant long-term trends, only for a few months of the year.

African dust transport and deposition modelling verified through a citizen science campaign in Finland

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

Transboundary transport of non-east and East Asian dust observed at Dunhuang, northwest China

Long-range transport of North African and Middle Eastern dust has been frequently observed in East Asia. However, understanding of their characteristics and effects in this region is insufficient. In this study, the transboundary transport of multi-source dust was captured by a polarized micro-pulse lidar from April 5 to 10, 2012, during a field campaign in Dunhuang, northwest China. Six dust plumes (DN1-DN6) were selected based on the spatiotemporal evolution of the depolarization ratio. Furthermore, the source, vertical characteristics of the coarse and fine components and their contributions were investigated by combining lidar observation with the WRF-Chem model simulation. The results indicated that DN1 was from Central Asia and it took approximately 4–5 days. DN2 originated from sources in North Africa and the Middle East and took approximately 6–7 days to reach Dunhuang. Samples DN3-DN6 originated from the Taklimakan and Gobi deserts in East Asia. A noticeable contrast was observed in the vertical distribution of the coarse and fine components between the long-range transported (DN1∼DN2) and fresh (DN3∼DN6) dust plumes. DN1 and DN2 presented comparable dust components (DD = Dc + Df, where Dc and Df are coarse- and fine-mode dust, respectively) and non-dust (ND) component contributions and a high predominance of Dc particles was present with at least 40% of total components in DN3-DN4. The contribution of ND particles was nearly negligible in DN5 and DN6. Lidar observations and model simulation both indicated that the maximum contribution of North African and Middle Eastern dust to the local aerosol loading exceeded 58%. However, the model simulation underestimated the contribution of DN1 by an average of 18% compared to lidar observations because DN1 was not reproduced well. This implies that the vertical distribution of dust should be carefully considered when dust impacts (e.g., radiation effects and air quality) are finely assessed using a model on a regional scale.

Long-Term Analysis of Aerosol Concentrations Using a Low-Cost Sensor: Monitoring African Dust Outbreaks in a Suburban Environment in the Canary Islands.

This study presents the results of the long-term monitoring of PM10 and PM2.5 concentrations using a low-cost particle sensor installed in a suburban environment in the Canary Islands. A laser-scattering Nova Fitness SDS011 sensor was operated continuously for approximately three and a half years, which is longer than most other studies using this type of sensor. The impact of African dust outbreaks on the aerosol concentrations was assessed, showing a significant increase in both PM10 and PM2.5 concentrations during the outbreaks. Additionally, a good correlation was found with a nearby reference instrument of the air quality network of the Canary Islands' government. The correlation between the PM10 and PM2.5 concentrations, the effect of relative humidity, and the stability of the sensor were also investigated. This study highlights the potential of this kind of sensor for long-term air quality monitoring with a view to developing extensive and dense low-cost air quality networks that are complementary to official air quality networks.