Continental impact on marine boundary layer coarse particles over the Atlantic Ocean between Europe and Antarctica |
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| Authors: | Jarkko V Niemi Heikki Tervahattu Aki Virkkula Risto Hillamo Kimmo Teinil Ismo K Koponen Markku Kulmala |
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| Institution: | aDepartment of Biological and Environmental Sciences, University of Helsinki, P.O. Box 27, FIN-00014 Helsinki, Finland;bNordic Envicon Ltd., Koetilantie 3, FIN-00790 Helsinki, Finland;cCooperative Institute for Research in Environmental Sciences, University of Colorado, Campus Box 216, Boulder, CO 80309, USA;dFinnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland;eDepartment of Physical Sciences, Division of Atmospheric Sciences, University of Helsinki, P.O. Box 64, FIN-00014 Helsinki, Finland |
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| Abstract: | Aerosol samples were collected in the Atlantic marine boundary layer between the English Channel and Antarctica during November–December 1999. The composition of coarse (aerodynamic diameter  1–3 μm) individual aerosol particles was studied using the SEM/EDX method. The major particle types observed were fresh sea salt, sea-salt particles reacted partly or totally with sulphuric acid or nitric acid, Mg-sulphate, Ca-sulphate, mixed aluminosilicates and sea salt, aluminosilicates, Ca-rich particles and Fe-rich particles. The relative fractions of sea-salt particles with moderate or strong Cl depletion were high near the coasts of Europe (65–74%) and Northern Africa (44–87%), low far from the coast of Western Africa (10–20%) and very low in remote sea areas between Africa and Antarctica (1%). The Cl depletion was strongest when air masses arrived from the direction of anthropogenic pollution sources. The fractions of Mg-sulphate particles were high (18–25%) in 2 samples near Europe. The Mg-sulphate particles were probably formed as a result of fractional recrystallization of sea-salt particles in which Cl was substituted by sulphate. It remained unclear whether these particles were formed in the atmosphere or during and after sampling. The relative fractions of particles from continental sources were quite low (10–15%) near Europe, very high (25–78%) near the coast of Northwestern Africa and very low in the remote sea areas (0–2%). Most of the continental particles were aluminosilicates and some of them were internally mixed with sea salt. Near the coast of Northwestern Africa, the main source of aluminosilicates was Saharan dust, and near the Gulf of Guinea, emissions from biomass burning were also mixed with aluminosilicates and sea salt. |
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| Keywords: | Individual particle analysis Marine aerosols Cl depletion Fractional recrystallization Continental sources Saharan dust |
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