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| Titel |
In situ measurements of aerosol optical properties and number size distributions in a coastal region of Norway during the summer of 2008 |
| VerfasserIn |
S. Mogo, V. E. Cachorro, J. F. López, E. Montilla, B. Torres, E. Rodríguez, Y. Bennouna, A. M. Frutos |
| 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 ; 12, no. 13 ; Nr. 12, no. 13 (2012-07-06), S.5841-5857 |
| Datensatznummer |
250011302
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| Publikation (Nr.) |
 copernicus.org/acp-12-5841-2012.pdf |
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| Zusammenfassung |
In situ measurements of aerosol optical properties and particle size distributions were made in
the summer of 2008 at the ALOMAR station facility (69°16' N, 16°00' E), located in a rural site in the north of the
island of Andøya (Vesterålen archipelago), approximately 300 km north of the Arctic
Circle. The extended three-month campaign was part of the POLARCAT Project (Polar Study using
Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and
Transport) of the International Polar Year (IPY-2007-2008). Our goal was to characterize the
aerosols of this sub-Arctic area, which are frequently transported to the Arctic region.
Data from 13 June to 26 August 2008 were available and the statistical
data for all instruments were calculated based on the hourly averages. The
overall data coverage was approximately 72%. The hourly mean values of the
light-scattering coefficient, σs, and the light-absorption
coefficient, σa, at 550 nm were 5.41 Mm−1
(StD = 3.55 Mm−1) and 0.40 Mm−1
(StD = 0.27 Mm−1), respectively. The scattering/absorption Ångström exponents,
αs,a, were used in a detailed analysis of the variations of the spectral shape
of σs,a. While αs indicates the presence of two
particle sizes corresponding to two types of aerosols, αa indicates only
one type of absorbing aerosol particle. αa values greater than 1 were not
observed. The single-scattering albedo, ω0, ranged from 0.62 to 0.99 (mean = 0.91,
StD = 0.05), and the relationships between this parameter and the absorption/scattering coefficients
and the Ångström exponents are presented. Any absorption value may
lead to the lowest values of ω0, whereas only the lowest scattering
values were observed in the lowest range of ω0. For a given
absorption value, lower ω0 were observed for smaller
αs. The submicrometer, micrometer and total concentrations
of the particles presented hourly mean values of 1277 cm−3
(StD = 1563 cm−3), 1 cm−3 (StD = 1 cm−3) and
2463 cm−3 (StD = 4251 cm−3), respectively, and the modal
correlations were also investigated. The optical and microphysical
parameters, as well as their relationship with each other, are reported.
σs correlated strongly with the number concentration of
accumulation mode particles and more strongly with the micrometer fraction of
particles, but weak correlations were observed for the Aitken and nucleation
modes. The origins and pathways of the air masses were examined, and based on
sector classification, a relationship between the air mass origin, the
optical parameters and the size distributions was established.
The low values of the optical and microphysical parameters indicate that the
predominant regional aerosol is mostly clean and the shape of the size
distribution is characterized by bimodal median size distributions. However,
the relationships between the air mass origins and the parameters studied
allow us to describe two characteristic situations: the one of the northern
and western air masses, which were predominantly composed of marine aerosols
and presented the lowest optical and microphysical values observed,
indicating predominantly non-absorbent and coarser particles; and the one of
the eastern and southern air masses, in which continental aerosols were
predominant and exhibited higher values for all parameters, indicating the
presence of smaller absorbent particles. The north-northeastern air masses
presented the strongest Aitken mode, indicating more recently formed
particles, and the southeastern air masses presented the strongest
accumulation mode (however, the southeastern air masses were the least
common, accounting for only 3% of occurrences). |
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