69 macla nº 15. septiembre 2011 revista de la sociedad española de mineralogía Variations on the Mineralogical Particle Properties of Atmospheric Saharan Dust from Different Source Regions / ESTHER COZ (1,*), TERESA MORENO (2), BEGOÑA ARTÍÑANO (1) (1) Departamento de Medio Ambiente, CIEMAT, Avenida Complutense 22. E28040 Madrid (Spain) (2) Instituto de Diagnóstico Ambiental y Estudios del Agua (IDÆA), CSIC, C/ Jordi Girona 18-26. E 08034 Barcelona (Spain) INTRODUCTION. The geographical proximity of the Sahara-Sahel dust corridor to the Mediterranean basin and the occurrence of certain meteorological scenarios favour intense dust episodes over the whole basin and strongly affect the surface PM10 ambient levels (Moreno et al., 2005). In some particular cases such as in the central region of the Iberian Peninsula (IP), African dust storms from long-range transport, jointly with regional recirculation, make of mineral dust the main contributor to the PM10 mass. The presence of dust, which can act as Cloud Condensation Nuclei (CCN) and Ice Nuclei (IC), is known to affect cloud optical properties and the formation of rain. It also affects the climate system by changing the energy balance of solar and thermal radiation (IPCC, 2007). But mineral dust does not travel alone. Several types of pollen and fungi spores together with several thousand types of microorganisms, very different from the native species, are also transported and can influence ecosystems and human health. In addition, interactions with other species during transport can modify its physicochemical and optical properties and serve as condensation nuclei for species such as organics, sulphates or chlorine. As a positive factor dust can also act as a fertilizer, providing nutrients to both marine and terrestrial ecosystems. This study focuses on the relationships between the elemental composition and morphology of individual dust particles from intense Saharan dust outbreaks over the Iberian Peninsula. Characteristics of local and regional resuspended mineral dust are also discussed and compared with those of Saharan dust. Morphology seems to be crucial in determining the dust plume characteristics, the variability during transportation and some physicochemical properties such as CCN activation. CCSEM/EDX METHODS. Single particle analysis of more than 100,000 particles was performed using a fully Computer-Controlled Scanning Electron Microscope coupled to Energy- Dispersive X-ray Spectroscopy (CCSEM/EDS). Clustering from the relative elemental composition amongst 18 different elements and morphological classification from the aspect ratio (AR=Length/Width, Fig.1) were carried out, which allowed the differentiation between episodes linked to diverse origins (Coz et al., 2009). Reproducibility of the samples and details regarding procedure limitations can be found in this reference. fig 1. Length, width and height measures on an atmospheric dust particle. TRANSPORT SEASONALITY & SOURCE REGIONS. While the Saharan dust transport following Atlantic pathways is a semi- permanent phenomenon associated to the presence of trade winds, a similar transport towards Southern Europe and the Mediterranean basin is less frequent and requires the occurrence of specific synoptic scenarios. Mineral dust transport from North Africa can be observed at any time of the year; however, the frequency of the events is much greater in certain periods (Escudero et al., 2005; Coz et al., 2009): Late winter and early spring period. Two different synoptic scenarios are characteristic from this period: a low pressure system at low atmospheric levels located to the West of Portugal, with typical associated origin in the Northern African margin (AFR-1); and a transport with a Mediterranean path entering the Iberian Peninsula (IP) with origin over the Morocco-Algeria-Tunisia region (AFR-2). Summer and early autumn period. Two other characteristics scenarios can be linked to this period: an anticyclone located to the East or Southeast of the Iberian Peninsula sometimes over Algeria and Tunisia (AFR-3); and a scenario associated to thermal low pressure systems that develop in summer, sometimes overlapping to the previous case study (AFR-4). SOIL VERSUS AEROSOL MINERALOGY. Saharan dust is comprised mostly of calcite-dolomite, quartz, clays, micas, feldspars, gypsum and other minerals in smaller amounts (Avila et al.,1997; Coz et al., 2009). The silicate fraction dominates the total contribution, with a major presence of clays, which contribute to large components of North African topsoil (Moreno et al., 2006). It has been already shown that Saharan incursions contribute to increase the relative abundance of silicates in the atmospheric picture independently of the emplacement of the receptor site in the IP and the associated topsoil composition (Coz et al., 2010). Fig. 2 shows the trajectories and origins of the previously described transports into central Iberian Peninsula and relative abundance of clay minerals at the palabras clave: Polvo mineral sahariano, CCSEM/EDX, Mineralogía, Morfología. key words: Saharan dust, CCSEM/EDX, Mineralogy, Morphology. resumen SEM 2011 * corresponding author: esther.coz@ciemat.es