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| Titel |
Hygroscopic growth of urban aerosol particles in Beijing (China) during wintertime: a comparison of three experimental methods |
| VerfasserIn |
J. Meier, B. Wehner, A. Maßling, W. Birmili, A. Nowak, T. Gnauk, E. Brüggemann, H. Herrmann, H. Min, A. Wiedensohler |
| 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 ; 9, no. 18 ; Nr. 9, no. 18 (2009-09-21), S.6865-6880 |
| Datensatznummer |
250007637
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| Publikation (Nr.) |
 copernicus.org/acp-9-6865-2009.pdf |
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| Zusammenfassung |
| The hygroscopic properties of atmospheric aerosols are highly relevant for
the quantification of radiative effects in the atmosphere, but also of
interest for the assessment of particle health effects upon inhalation.
This article reports measurements of aerosol particle hygroscopicity in
the highly polluted urban atmosphere of Beijing, China in January 2005.
The meteorological conditions corresponded to a relatively cold and dry
atmosphere. Three different methods were used: 1) A combination of Humidifying
Differential Mobility Particle Sizer (H-DMPS) and Twin Differential
Mobility Particle Sizer (TDMPS) measurements, 2) A
Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA), and 3) A
simplistic solubility model fed by chemical particle composition determined
from Micro Orifice Uniform Deposit Impactor (MOUDI) samples. From the
H-DMPS and TDMPS particle number size distributions, a size-resolved
descriptive hygroscopic growth factor (DHGF) was determined for the relative
humidities (RH) 55%, 77% and 90%, and particle diameters between 30 and
400 nm. In Beijing, the highest DHGFs were observed for accumulation mode
particles, 1.40 (±0.03) at 90% RH. DHGF decreased significantly with
particle size, reaching 1.04 (±0.15) at 30 nm. H-TDMA data
also suggest a decrease in growth factor towards the biggest particles
investigated (350 nm), associated with an increasing fraction of nearly
hydrophobic particles. The agreement between the H-DMPS/TDMPS and
H-TDMA methods was satisfactory in the accumulation mode size range
(100–400 nm). In the Aitken mode range (<100 nm), the H-DMPS/TDMPS
method yielded growth factors lower by up to 0.1 at 90% RH. The application of
the solubility model based on measured chemical composition clearly reproduced
the size-dependent trend in hygroscopic particle growth observed by the other
methods. In the case of aerosol dominated by inorganic ions, the composition-derived
growth factors tended to agree (± 0.05) or underestimate (up to 0.1) the
values measured by the other two methods. In the case of aerosol dominated by
organics, the reverse was true, with an overestimation of up to 0.2. The results
shed light on the experimental and methodological uncertainties that are still
connected with the determination of hygroscopic growth factors. |
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