DOI: 10.1594/pangaea.848498
title: Long-term chemical characterization of aerosols at CVAO from 2007 to 2011

description: The first long-term aerosol sampling and chemical characterization results from measurements at the Cape Verde Atmospheric Observatory (CVAO) on the island of São Vicente are presented and are discussed with respect to air mass origin and seasonal trends. In total 671 samples were collected using a high-volume PM10 sampler on quartz fiber filters from January 2007 to December 2011. The samples were analyzed for their aerosol chemical composition, including their ionic and organic constituents. Back trajectory analyses showed that the aerosol at CVAO was strongly influenced by emissions from Europe and Africa, with the latter often responsible for high mineral dust loading. Sea salt and mineral dust dominated the aerosol mass and made up in total about 80% of the aerosol mass. The 5-year PM10 mean was 47.1 ± 55.5 µg/m**2, while the mineral dust and sea salt means were 27.9 ± 48.7 and 11.1 ± 5.5 µg/m**2, respectively. Non-sea-salt (nss) sulfate made up 62% of the total sulfate and originated from both long-range transport from Africa or Europe and marine sources. Strong seasonal variation was observed for the aerosol components. While nitrate showed no clear seasonal variation with an annual mean of 1.1 ± 0.6 µg/m**3, the aerosol mass, OC (organic carbon) and EC (elemental carbon), showed strong winter maxima due to strong influence of African air mass inflow. Additionally during summer, elevated concentrations of OM were observed originating from marine emissions. A summer maximum was observed for non-sea-salt sulfate and was connected to periods when air mass inflow was predominantly of marine origin, indicating that marine biogenic emissions were a significant source. Ammonium showed a distinct maximum in spring and coincided with ocean surface water chlorophyll a concentrations. Good correlations were also observed between nss-sulfate and oxalate during the summer and winter seasons, indicating a likely photochemical in-cloud processing of the marine and anthropogenic precursors of these species. High temporal variability was observed in both chloride and bromide depletion, differing significantly within the seasons, air mass history and Saharan dust concentration. Chloride (bromide) depletion varied from 8.8 ± 8.5% (62 ± 42%) in Saharan-dust-dominated air mass to 30 ± 12% (87 ± 11%) in polluted Europe air masses. During summer, bromide depletion often reached 100% in marine as well as in polluted continental samples. In addition to the influence of the aerosol acidic components, photochemistry was one of the main drivers of halogenide depletion during the summer; while during dust events, displacement reaction with nitric acid was found to be the dominant mechanism. Positive matrix factorization (PMF) analysis identified three major aerosol sources: sea salt, aged sea salt and long-range transport. The ionic budget was dominated by the first two of these factors, while the long-range transport factor could only account for about 14% of the total observed ionic mass.
description: The sampling regime has been changed several times. All changes are described by Fomba et al. (2014). The PM10 filter were stored in a freezer at Mindelo and transported frozen from Minelo to Germany to TROPOS. The sampling height was 32 m above ground (42 m above sea level), normally. During the time of construction of the new wooden tower the sampling took place between 23-Oct-2009 (Filter No. 371) and 09-Jul-2010 (Filter No. 499) on top of the laboratory container (4 m above ground or 14 m above sea level). These samples are strongly influenced by direct sea spray.Organic and elemental carbon were analyzed by a two-step thermographic method (C-mat 5500, Ströhlein, Germany) with nondispersive infrared sensor (NDIR) detection as described in Neusüss et al. (2002, doi:10.1029/2001JD000514), Gnauk et al. (2008, doi:10.1016/j.atmosenv.2008.05.001) and Carpenter et al. (2010, doi:10.1007/s10874-011-9206-1). The detection limits for quartz fiber filter analysis were 30 ng/m**3 for EC and 100 ng/m**3 for OC.
description: Supplement to: Fomba, Khanneh Wadinga; Müller, Konrad; van Pinxteren, Dominik; Poulain, Laurent; van Pinxteren, Manuela; Herrmann, Hartmut (2014): Long-term chemical characterization of tropical and marine aerosols at the Cape Verde Atmospheric Observatory (CVAO) from 2007 to 2011. Atmospheric Chemistry and Physics, 14(17), 8883-8904