Abstract Fourteen samples of deposited atmospheric dust collected during desert dust intrusions over Granada in the summer of 2010 are studied here. During these atmospheric dust events the PM10 ranged from 25 μg m−3 to 200 μg m−3, surpassing occasionally the standard limit (50 μg m−3) established by the European Union Directive as a risk for the human health. The mineralogical composition of the dust samples is very heterogeneous, showing that the origin of collected particles is from north-northwest of Africa and local/regional soils. The analyzed dust samples contain between 1 and 9% of iberulites, polymineral spherical particles with diameter between 34 and 111 μm. New compositional results obtained by mapping chemical elements and mineral compositions of iberulites with VPSEM-EDEX technology allowed as to go further than previous studies and provide new insight on the iberulites genesis. The SEM-microstructure analysis of the iberulites and the compositional results obtained by VPSEM-EDEX technique showed that clay and sulphur components are important in determining their spherical shapes. The analysis also shows that iberulites present a typical vortex at one of the poles and an external covering by nano-clays in laminar clusters, a form of rind and a core internal with sizes less than 10 μm. On the other hand, the micromorphological analysis evidences that the bacteria and its polymeric exudates participate in the iberulite genesis, acting as aggregation agents and contributing to its protection and compensating its fragility. The role of bacteria and its polymeric exudates in the iberulite genesis has not been described previously, and it would explain the flux, transport and survival of tropospheric microorganisms over long distances. These new observations and finding led us to take into account the role of bacteria in iberulite genesis and to reconsider the previous hypothesis regarding the iberulite genesis proposed in previous works.

中文翻译：

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格拉纳达盆地（伊比利亚半岛南部）的尘埃和岩屑侵入。大气白斑的成因与形成

摘要 这里研究了 2010 年夏季格拉纳达沙漠尘埃入侵期间收集的 14 个沉积大气尘埃样本。在这些大气尘埃事件中，PM10 的范围从 25 μg m-3 到 200 μg m-3，偶尔会超过欧盟指令确定的对人类健康构成风险的标准限值（50 μg m-3）。灰尘样品的矿物组成非常不均匀，表明收集到的颗粒来自非洲的西北和西北地区以及当地/区域土壤。所分析的粉尘样本含有 1% 至 9% 的 iberulites，即直径在 34 至 111 μm 之间的多矿物球形颗粒。通过使用 VPSEM-EDEX 技术绘制 iberulites 的化学元素和矿物成分图获得的新成分结果允许比以前的研究更进一步，并提供对 iberulites 成因的新见解。通过 VPSEM-EDEX 技术获得的 SEM 显微结构分析和 VPSEM-EDEX 技术获得的成分结果表明，粘土和硫成分对于确定其球形形状很重要。分析还表明，iberulites 在其中一个极点处呈现出典型的涡流，外部覆盖着层状簇中的纳米粘土，这是一种外皮和内部尺寸小于 10 μm 的核心。另一方面，显微形态分析表明细菌及其聚合物渗出物参与了白斑的发生，充当聚集剂并促进其保护并补偿其脆弱性。细菌及其聚合渗出液在 iberulite 成因中的作用以前没有被描述过，它可以解释对流层微生物长距离的流动、运输和存活。这些新的观察和发现使我们考虑到细菌在白斑成因中的作用，并重新考虑先前工作中提出的关于白斑成因的假设。