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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 8939-8958, 2017
https://doi.org/10.5194/acp-17-8939-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
25 Jul 2017
Speciation of organic aerosols in the Saharan Air Layer and in the free troposphere westerlies
M. Isabel García1,2, Barend L. van Drooge3, Sergio Rodríguez1, and Andrés Alastuey3 1Izaña Atmospheric Research Centre, AEMET, Joint Research Unit to CSIC Studies on Atmospheric Pollution, Santa Cruz de Tenerife, 38001, Spain
2Department of Chemistry (T.U. Analytical Chemistry), Faculty of Science, University of La Laguna, La Laguna, 38206, Spain
3Institute of Environmental Assessment and Water Research, CSIC, Barcelona, 08034, Spain
Abstract. We focused this research on the composition of the organic aerosols transported in the two main airflows of the subtropical North Atlantic free troposphere: (i) the Saharan Air Layer – the warm, dry and dusty airstream that expands from North Africa to the Americas at subtropical and tropical latitudes – and (ii) the westerlies, which flow from North America over the North Atlantic at mid- and subtropical latitudes. We determined the inorganic compounds (secondary inorganic species and elemental composition), elemental carbon and the organic fraction (bulk organic carbon and organic speciation) present in the aerosol collected at Izaña Observatory,  ∼  2400 m a.s.l. on the island of Tenerife. The concentrations of all inorganic and almost all organic compounds were higher in the Saharan Air Layer than in the westerlies, with bulk organic matter concentrations within the range 0.02–4.0 µg m−3. In the Saharan Air Layer, the total aerosol population was by far dominated by dust (93 % of bulk mass), which was mixed with secondary inorganic pollutants ( <  5 %) and organic matter ( ∼  1.5 %). The chemical speciation of the organic aerosols (levoglucosan, dicarboxylic acids, saccharides, n-alkanes, hopanes, polycyclic aromatic hydrocarbons and those formed after oxidation of α-pinene and isoprene, determined by gas chromatography coupled with mass spectrometry) accounted for 15 % of the bulk organic matter (determined by the thermo-optical transmission technique); the most abundant organic compounds were saccharides (associated with surface soils), secondary organic aerosols linked to oxidation of biogenic isoprene (SOA ISO) and dicarboxylic acids (linked to several primary sources and SOA). When the Saharan Air Layer shifted southward, Izaña was within the westerlies stream and organic matter accounted for  ∼  28 % of the bulk mass of aerosols. In the westerlies, the organic aerosol species determined accounted for 64 % of the bulk organic matter, with SOA ISO and dicarboxylic acids being the most abundant; the highest concentration of organic matter (3.6 µg m−3) and of some organic species (e.g. levoglucosan and some dicarboxylic acids) were associated with biomass burning linked to a fire in North America. In the Saharan Air Layer, the correlation found between SOA ISO and nitrate suggests a large-scale impact of enhancement of the formation rate of secondary organic aerosols due to interaction with anthropogenic NOx emissions.

Citation: García, M. I., van Drooge, B. L., Rodríguez, S., and Alastuey, A.: Speciation of organic aerosols in the Saharan Air Layer and in the free troposphere westerlies, Atmos. Chem. Phys., 17, 8939-8958, https://doi.org/10.5194/acp-17-8939-2017, 2017.
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Short summary
Speciation of organic aerosol was performed in the westerlies and in the Saharan Air Layer, where biogenic secondary organic aerosol (oxidation of isoprene and alpha-pinene) and primary combustion compounds (hopanes and PAHs) were observed. In the Saharan Air Layer, species (saccharides) linked to soil emission – plant tissues and microorganisms – in the inner Sahara were also identified, whereas in the westerlies biomass burning compounds (e.g. levoglucosan) from North America also occurred.
Speciation of organic aerosol was performed in the westerlies and in the Saharan Air Layer,...
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