Aerosol size-resolved trace metal composition in remote northern tropical Atlantic marine environment: case study Cape Verde islands

Abstract

Size-resolved trace metal concentrations of 15 elements in aerosol particles at the Cape Verde Atmospheric Observatory (CVAO) under remote background conditions were investigated through analysis of aerosol samples collected during intensive field studies from January 2007 to November 2011 using total reflection x-ray fluorescence (TXRF). The identification of the main air mass origin that influence remote marine aerosol in the northern tropical Atlantic has been investigated. In total, 317 samples were collected. The dataset was analyzed according to the main air mass inflow at the station. We found that remote conditions make up about 45% of the meteorological conditions in a year at CVAO and thus the northern tropical Atlantic. Surprisingly, air masses from North America are often responsible for higher trace metal concentrations in this region. <br></br> Elements such as Zn, Pb, Cu, Cr, Ni, and V were mostly found in the submicron size fractions, while elements with dominant crustal or oceanic origin such as Fe, Ti, Mn, Sr, and Rb were found in the coarse fractions (>1 μm). The highest metal concentrations, especially for Zn (3.23 ng m⁻³), Cu (0.81 ng m⁻³), Sr (2.63 ng m⁻³), and Cr (0.53 ng m⁻³), were observed in air masses originating from North America and the concentrations were within the same concentration range to those reported previously in the literature for remote marine aerosols. Fe (12.26 ng m⁻³), Ti (0.91 ng m⁻³), and Mn (0.35 ng m⁻³) showed higher concentrations when air mass came from Europe and the Canary Islands. Pb concentration was low (<0.20 ng m⁻³) and did not vary significantly with air mass direction. The low Pb concentration is indicative of the complete phase-out of leaded gasoline even in African countries. Crustal enrichment factor values decreased from fine to coarse-mode particles with low values (<4) observed for Fe, Mn, and Rb, and high values (>20) for Zn, Cu, Ni, Cr, Pb, and Se. The observed enrichment of the elements was attributed to crustal, marine, anthropogenic, and biogenic sources, as well as long-range transport and resuspension. Zn, Cu and Pb were indicators of anthropogenic activities, while Ti and Sr were indicators of crustal and marine origin, respectively. Oceanic and biogenic emissions might have contributed to most of the Se observed. This work provides the first long-term size-resolved trace metals study for remote tropical northern Atlantic marine aerosols and the dataset could serve as good initiation of yearly flux estimates

Elemental ratios and enrichment factors in aerosols from the US-GEOTRACES North Atlantic transects

“…Fe and Mn, have also been observed as enriched in anthropogenically-impacted aerosols (e.g. Sholkovitz et al, 2012;Fomba et al, 2013). Sea-spray generated at the seawater surface by wind and waves has also been proposed as a mechanism for enriching TMs in aerosols (Weisel et al, 1984;Arimoto et al, 2003), using TM/Na ratios based on surface seawater concentrations.…”

Concentrations and solubility of trace elements in fine particles at a mountain site, southern China: regional sources and cloud processing

“…Lushan (Li et al, 2013). Almost all of the metal particles were found to be internally mixed within S-rich cloud residues with the encapsulation of cloud water and presented a nearly spherical shape or aggregation, suggesting the likely sources to be high-temperature coal combustion by coal-fired power plants and industries, during which industrial gases containing abundant SO 2 and metals were released, followed by the generation of metal-sulfate particles (Gieré et al, 2006). Figure 11 also demonstrates the small diameters of the metal particles in cloud residues much smaller than 1 µm, especially for the aggregation of spherical Fe nanoparticles embedded in aged S-rich residues (Fig.…”

Atmospheric transport of trace elements and nutrients to the oceans

“…EFs less than 10 are often interpreted with caution in terms of providing clear evidence of additional sources beyond crustal material, owing to the compound uncertainties in the analyses and the crustal ratios, but for a number of metals such as zinc, copper, chromium, vanadium and lead (at least during the period of the extensive use of lead in fuel), enrichments are large and clearly imply a non-crustal and probably anthropogenic high temperature source [38]. Table 5 presents EFs for a number of elements in aerosols from the North Atlantic collected at Cape Verde arriving from the North Atlantic in air masses that have spent several days over the sea [13]. The EFs indicate that for V, Zn, Cu, Ni, Cr and Pb, concentrations are higher than would be predicted from their crustal abundance, and this together with the dominance of the fine mode aerosol size distribution for these elements suggests that high temperature anthropogenic emissions are the main sources of these metals [13,64].…”

“…The pattern of large enrichments of some metals (V, Cr, Ni, Cu, Zn and Pb) and small enrichments of others (Mn, Fe and also other elements including Ba, U, Th and rare earth elements) is seen in many datasets [12,13,15,38,67] and has persisted for many years, with similar values and patterns evident in data from the 1970s [64]. Lead, for which there has been a significant change owing to elimination of lead additions to automobile fuels [68], is an exception to this.…”