 |
| Titel |
Hygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: implications for regional direct radiative forcing under clean and polluted conditions |
| VerfasserIn |
M. Stock, Y. F. Cheng, W. Birmili, A. Maßling, B. Wehner, T. Müller, S. Leinert, N. Kalivitis, N. Mihalopoulos, A. Wiedensohler |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 9 ; Nr. 11, no. 9 (2011-05-09), S.4251-4271 |
| Datensatznummer |
250009702
|
| Publikation (Nr.) |
 copernicus.org/acp-11-4251-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| This work examines the effect of direct radiative
forcing of aerosols in the eastern Mediterranean troposphere as a function of
air mass composition, particle size distribution and hygroscopicity, and
relative humidity (RH). During intensive field measurements on the island of
Crete, Greece, the hygroscopic properties of atmospheric particles were
determined using a Hygroscopicity Tandem Differential Mobility Analyzer
(H-TDMA) and a Hygroscopicity Differential Mobility
Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former
studies, the H-TDMA identified three hygroscopic sub-fractions of
particles in the sub-μm range: a more hygroscopic group, a less
hygroscopic group and a nearly hydrophobic particle group. The average
hygroscopic particle growth factors at 90 % RH were a significant
function of particle mobility diameter (Dp): 1.42 (± 0.05) at 30 nm
compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified
up to three hygroscopic sub-fractions at mobility diameters of 1.0 and
1.2 μm. The data recorded between 12 August and 20 October 2005
were classified into four distinct synoptic-scale air mass types
distinguishing between different regions of origin (western Mediterranean vs.
the Aegean Sea) as well as the degree of continental pollution (marine vs.
continentally influenced). The hygroscopic properties of particles with
diameter Dp≥150 nm showed the most pronounced dependency on air mass
origin, with growth factors in marine air masses exceeding those in
continentally influenced air masses. Particle size distributions and
hygroscopic growth factors were used to calculate aerosol light scattering
coefficients at ambient RH using a Mie model. A main result was the
pronounced enhancement of particle scattering over the eastern Mediterranean
due to hygroscopic growth, both in the marine and continentally influenced
air masses. When RH reached its summer daytime values around 70–80 %, up
to 50–70 % of the calculated visibility reduction was due to the
hygroscopic growth of the particles by water compared to the effect of the
dry particles alone. The estimated aerosol direct radiative forcings for
both, marine and continentally influenced air masses were negative indicating
a net cooling of the atmosphere due to the aerosol. The radiative forcing
ΔFr was nevertheless governed by the total aerosol
concentration most of the time: ΔFr was typically more
negative for continentally influenced aerosols (ca. −4 W m−2)
compared to rather clean marine aerosols (ca. −1.5 W m−2). When RH
occasionally reached 90 % in marine air masses, ΔFr even
reached values down to −7 W m−2. Our results emphasize, on the basis
of explicit particle hygroscopicity measurements, the relevance of ambient RH
for the radiative forcing of regional atmospheres. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|