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| Titel |
Hygroscopic properties of aerosol particles at high relative humidity and their diurnal variations in the North China Plain |
| VerfasserIn |
P. F. Liu, C. S. Zhao, T. Göbel, E. Hallbauer, A. Nowak, L. Ran, W. Y. Xu, Z. Z. Deng, N. Ma, K. Mildenberger, S. Henning, F. Stratmann, 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 ; 11, no. 7 ; Nr. 11, no. 7 (2011-04-14), S.3479-3494 |
| Datensatznummer |
250009606
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| Publikation (Nr.) |
 copernicus.org/acp-11-3479-2011.pdf |
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| Zusammenfassung |
| The hygroscopic properties of submicron aerosol particles were determined at
a suburban site (Wuqing) in the North China Plain among a cluster of cities
during the period 17 July to 12 August, 2009. A High Humidity Tandem
Differential Mobility Analyser (HH-TDMA) instrument was applied to measure
the hygroscopic growth factor (GF) at 90%, 95% and 98.5% relative
humidity (RH) for particles with dry diameters between 50 and 250 nm. The
probability distribution of GF (GF-PDF) averaged over the period shows a
distinct bimodal pattern, namely, a dominant more-hygroscopic (MH) group and
a smaller nearly-hydrophobic (NH) group. The MH group particles were highly
hygroscopic, and their GF was relatively constant during the period with
average values of 1.54 ± 0.02, 1.81 ± 0.04 and 2.45 ± 0.07 at
90%, 95% and 98.5% RH (D0 = 100 nm), respectively. The NH group
particles grew very slightly when exposed to high RH, with GF values of
1.08 ± 0.02, 1.13 ± 0.06 and 1.24 ± 0.13 respectively at 90%,
95% and 98.5% RH (D0 = 100 nm). The hygroscopic growth behaviours at
different RHs were well represented by a single-parameter Köhler model.
Thus, the calculation of GF as a function of RH and dry diameter could be
facilitated by an empirical parameterization of κ as function of dry
diameter. A strong diurnal pattern in number fraction of different
hygroscopic groups was observed. The average number fraction of NH particles
during the day was about 8%, while during the nighttime fractions up to
20% were reached. Correspondingly, the state of mixing in terms of water
uptake varied significantly during a day. Simulations using a
particle-resolved aerosol box model (PartMC-MOSAIC) suggest that the diurnal
variations of aerosol hygroscopicity and mixing state were mainly caused by
the evolution of the atmospheric mixing layer. The shallow nocturnal
boundary layer during the night facilitated the accumulation of freshly
emitted carbonaceous particles (mainly hydrophobic) near the surface while
in the morning turbulence entrained the more aged and more hygroscopic
particles from aloft and diluted the NH particles near the surface resulting
in a decrease in the fraction of NH particles. |
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