The relative contributions of weathering and aeolian inputs to postglacial formation of Mediterranean alpine loess

Between the southern margin of the European loess belt and Sahara Desert, thin and irregularly distributed loess deposits occur in Mediterranean mountains. During the most recent deglaciation, along the Pleistocene-Holocene boundary, the deposition of glacial, periglacial and outwash sediments, was the main local source of Mediterranean alpine loess, whereas proximal alluvial planes comprised a secondary source. The mid-Holocene termination of African Humid Period and subsequent aridification of Sahara Desert occurred simultaneously with a change of the regional climate from Atlantic to Mediterranean-dominated, characterized by frequent episodes of southerly winds. This resulted to a change of the loess source, as deflation of quartz rich silts enriched in Zr during intense episodes of Sahara dust transport became more dominant. Here, a 32cm loess profile from the Plateau of Muses (PM), below the summit of Mount Olympus, Greece, is investigated on the basis of grain size, mineralogy, environmental magnetism and geochemistry. Comparisons of loess samples with glacial and periglacial deposits, enables us to differentiate relative contributions of local sources and allochthonous aeolian inputs. Calcite sand rich in feldspars makes up the glacial and periglacial clast free matrix. In contrast, PM loess is composed by clay and fine silt fractions with minor calcite sand contributions. The mineralogical matrix of loess contains quartz, phyllosilicates and mixed layer clays, while its geochemical composition contains high amounts of detrital Fe-Ti oxides and aeolian transported Al and Zr. Based on the multi-proxy approach applied here, the loess profile is partitioned in three layers. Holocene average deposition rates (~2.5 cm/ka) broadly agree with modern Sahara dust deposition (~2.0 cm/ka) and long-term postglacial Mediterranean mountain denudation rates (~0.5 cm/ka). Such low rates provided ample time for post depositional modifications, such as decalcification, deferrification and removal of K, evident from the trends of chemical weathering proxies Ca/Sr, Fe/Ti and K/Rb, respectively.

The impact of Sahara dust on air quality and public health in European countries

<p>The frequent transport of Sahara dust toward Europe degrades the air quality and poses risk to human health. In this study we use GEOS-Chem (a global transport model) to examine the impact of Sahara dust on air quality and the consequent health effect in Europe for the year 2016–2017. The simualtion is conducted in a nested model with the native resolution of 0.25° × 0.3125° (Latitude × Logitude) over Europe (32.75°N–61.25°N, 15°W–40°E). The simulation on a global scale with a coarse horizontal resolution of 2° × 2.5° is also conducted to provide the boundary condition for the nested-grid simulation as well as aerosol optical depth (AOD) over the Sahara desert for model evaluation.</p><p>The model performance is evaluated by comparisons with surface observations including aerosol optical depth (AOD) from AERONET, and PM<sub>2.5</sub> and PM<sub>10</sub> concentrations from numerous air quality monitoring stations in European countries. Overall, the model well reproduces observed surface PM concentrations over most European countries with some underestimation in southern Europe. In addition, model AOD is highly correlated with AERONET data over both Sahara and European region.</p><p>The spatial distribution of dust concentrations, frequency of dust episodes, as well as the exposure and health effects are studied. The concentrations of Sahara dust decrease from 5–20 μg m<sup>-3</sup> in south to 0.5–1.0 μg m<sup>-3</sup> in north of Europe. Spain and Italy are most heavily influenced by Sahara dust in terms of both concentration levels and frequencies of occurrence. Strong dust episodes (>50 μg m<sup>-3</sup>) occur predominately in Southern Spain and Italy with frequency of 2–5%, while light dust episodes (>1 μg m<sup>-3</sup>) are often detected (5–30%) in Central and Western Europe.</p><p>The population-weighted dust concentrations are higher in Southern European countries (3.3–7.9 μg m<sup>-3</sup>) and lower in Western European countries (0.5–0.6 μg m<sup>-3</sup>). The health effects of exposure to dust is evaluated based on population attributable fraction (PAF). We use the relative risk (RR) value of 1.04 (95% confidence intervals: 1.00 – 1.09) per 10 µg m<sup>-3 </sup>of dust exposure based on the main model of Beelen et al. (2014). We estimate a total of 41884 (95% CI: 2110–81658) deaths per year attributed to the exposure to dust in the 13 European countries studied. Due to high contribution to PM<sub>10</sub> in Spain, Italy and Portugal, dust accounts for 44%, 27% and 22% of the total number of deaths linked to PM<sub>10</sub> exposure, respectively.</p>

The Effect of Particulate Matter Pollution of Saharan Dust Over Europe in May-2020: A Case Study of Karaman City Center, Turkey

Desert dust rising from the African region and covered very long distances with meteorological events can be an important source of pollution for many countries from time to time. Although dust and sand masses that remain in the atmosphere for a long time are known to be inert and stable, but studies show that they affect vegetative production by changes in precipitation and radiation regimes. It is important for natural phenomena and has also revealed their effects in regions over which the atmospheric transport occurs. The Sahara dust storm of mid-May 2020 has strongly, affected many European countries. The Sahara dust and hot air transport is reported over the Mediterranean region to the Balkans and further to Turkey. Depending on the climatic conditions, the Sahara dust may remain in some regions for longer period. Rainy and humid weather conditions slow down the flow of dust and increase the settling rate in that region. In such cases it creates mud-like precipitation accompanying with rain. In this study, Sahara dust pollution effect is investigated for a particulate event pollution with the use of measurements from the network system in all cities in Turkey. For this purpose, the values of Particulate Matter (PM) pollution are analysed before the desert dust reached Turkey, during the event and when it left the country. PM measurement values in Karaman province were examined and it was shown that the Sahara dust increased significantly in the period when it reached this region. Then, PM values were seen to come down to normal levels.

Long-Range-Transported Mineral Dust From Africa and Middle East to East Asia Observed with the Asian Dust and Aerosol Lidar Observation Network (AD-Net)

Mineral dust generated in Africa and Middle East is sometimes transported to East Asia. Some cases were observed with the Asian Dust and aerosol lidar observation Network (AD-Net). In the large Sahara dust event in March 2018, which was reported by mass media as that snow in Sochi, Russia was stained into orange, the dust was transported to Sapporo, Japan in 4 days from Sochi and observed with the AD-Net lidar. Sahara dust events were also observed in April 2017 and April 2018 with AD-Net. The source areas and transport paths were studied with chemical transport models and trajectory analysis and also confirmed with CALIPSO data. This study showed that long-range transport from Africa and Middle East to East Asia is not rare in springtime.