Characterization of African dust transported to Puerto Rico by individual particle and size segregated bulk analysis

Abstract

[1] As part of the Puerto Rico Dust Experiment (PRIDE), airborne and surface dust particle samples from Africa were collected and subjected to bulk elemental and singleparticle analysis. Airborne samples were collected on polycarbonate filters at various altitudes and underwent single-particle scanning electron microscopy with energy dispersive analysis with X-rays (EDAX) to derive elemental ratios of key soil elements. Particle chemistry was related to size and morphological characteristics. At the principle surface site, particles were collected on a Davis Rotating Drum (DRUM) cascade impactor strips in eight stages from 0.1 to 12 mm at 4 hour time resolution. These samples were subjected to X-ray florescence (XRF) to determine bulk elemental composition from Al through Zn. The elemental data showed good correlation between the DRUM and the aircraft samples. Cluster analysis of single-particle data resulted in 63 statistically significant clusters. Several clusters can be easily related to their parent mineralogical species. However, as dust particles are to a large extent aggregates, most clusters are based on a continuum of varied mineralogical species and cannot be easily categorized. With 60,500 total particles counted from the airborne filters, a statistically significant number of large particles could be analyzed. Estimated mean surface area modal diameter is $5 mm, with an average aspect ratio of 1.9. An apparent change in source region is seen in the morphological data and non alumino-silicate minerals but is not seen in the aluminum to silicon ratio. We suspect homogenization during long-range transport.

Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition

“…1 in Klaver et al, 2011). We do not necessary regard this as a problem, as the atmospheric dust load, both in short-and large-scale transport, is often due to a variety of sources active at the same time (Glaccum and Prospero, 1980;Reid et al, 2003;Formenti et al, 2003;Schepanski et al, 2007;Laurent et al, 2008;McConnell et al, 2008;Marticorena et al, 2010). Also, this supra-imposition, both in the vertical and in the horizontal, is what is actually seen by spaceborne sensors.…”

“…The southern Sahara is the location of two of the most persistent dust sources on the global scale: the Bodélé depression in between the Tibesti and the Ennedi mountain chains in Chad and the areas in between the east of Mauritania, the north of Mali and the south of Algeria (Prospero et al, 2002;Laurent et al, 2008;Washington et al, 2006;Shao et al, 2011). These sources are relevant on the global scale as their emissions are transported across the Atlantic Ocean towards South and Central America (Reid et al, 2003;Koren et al, 2006;Ben-Ami et al, 2009.…”

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

“…Otto et al (2007) underlined the importance of the coarse particle fraction (particles of diameter D p > 3 µm) as well as the ratio between the fine and the coarse particle fraction on the optical properties (ω 0 , g). Dust particles are not spherical but generally have complex and irregular shapes (Reid et al, 2003;Kandler et al, 2007;Chou et al, 2008). Recent studies tend to show that the particle asphericity only induces differences in the order of few percent on ω 0 and g values (Mishchenko et al, 1997;Yang et al, 2007;Otto et al, 2009).…”

Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

“…Different field studies show AR median values ranging between 1.4 and 1.9 (Chou et al, 2006;Clarke et al, 2004;Reid et al, 2003;Kandler et al, 2006;Dubovik et al, 2006;Mishra et al, 2012). In this study, we modeled dust aerosols as spheroids and rectangular prisms with an intermediate aspect ratio (compared to the refereed literature) of 1.75, which has also been found in CARES, PICO, MILA-GRO and the ClearfLo field campaigns (see Table 3).…”

“…We generate synthetic BC aggregates by aggregation of monomers in random walk (Richard and Davis, 2008;Richard et al, 2011). The synthetic BC aggregates are characterized by a volume equivalent radius (a eff also defined as the radius of a sphere containing all the volume of the particle) between 82 and 144 nm, a constant monomer diameter of 40 nm and an open-chain-like structure.…”