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| Titel |
Long-term chemical characterization of tropical and marine aerosols at the Cape Verde Atmospheric Observatory (CVAO) from 2007 to 2011 |
| VerfasserIn |
K. W. Fomba, K. Müller, D. van Pinxteren, L. Poulain, M. van Pinxteren, H. Herrmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 17 ; Nr. 14, no. 17 (2014-09-01), S.8883-8904 |
| Datensatznummer |
250118989
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| Publikation (Nr.) |
 copernicus.org/acp-14-8883-2014.pdf |
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| Zusammenfassung |
| 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 \textpm 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. |
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