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| Titel |
Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing |
| VerfasserIn |
S. S. Gunthe, D. Rose, H. Su, R. M. Garland, P. Achtert, A. Nowak, A. Wiedensohler, M. Kuwata, N. Takegawa, Y. Kondo, M. Hu, M. Shao, T. Zhu, M. O. Andreae, U. Pöschl |
| 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. 21 ; Nr. 11, no. 21 (2011-11-08), S.11023-11039 |
| Datensatznummer |
250010173
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| Publikation (Nr.) |
 copernicus.org/acp-11-11023-2011.pdf |
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| Zusammenfassung |
Atmospheric aerosol particles serving as cloud condensation nuclei
(CCN) are key elements of the hydrological cycle and climate. CCN
properties were measured and characterized during the CAREBeijing-2006
campaign at a regional site south of the megacity of Beijing,
China. Size-resolved CCN efficiency spectra recorded for
a supersaturation range of S=0.07% to 0.86% yielded average
activation diameters in the range of 190 nm to 45 nm. The
corresponding effective hygroscopicity parameters (κ)
exhibited a strong size dependence ranging from ~0.25 in the
Aitken size range to ~0.45 in the accumulation size range. The
campaign average value (κ =0.3 ± 0.1) was similar to the
values observed and modeled for other populated continental regions.
The hygroscopicity parameters derived from the CCN measurements were
consistent with chemical composition data recorded by an aerosol mass
spectrometer (AMS) and thermo-optical measurements of apparent
elemental and organic carbon (EC and OC). The CCN
hygroscopicity and its size dependence could be parameterized as
a function of only AMS based organic and inorganic mass fractions
(forg, finorg) using the
simple mixing rule κp ≈ 0.1 · forg + 0.7
· finorg.
When the measured air masses originated from the north and passed
rapidly over the center of Beijing (fresh city pollution), the average
particle hygroscopicity was reduced (κ = 0.2 ± 0.1),
which is consistent with enhanced mass fractions of organic compounds
(~50%) and EC (~30%) in the fine
particulate matter (PM1). Moreover, substantial fractions
of externally mixed weakly CCN-active particles were observed at low
supersaturation (S=0.07%), which can be explained by the presence
of freshly emitted soot particles with very low hygroscopicity
(κ < 0.1). Particles in stagnant air from the industrialized
region south of Beijing (aged regional pollution) were on average
larger and more hygroscopic, which is consistent with enhanced mass
fractions (~60%) of soluble inorganic ions (mostly sulfate,
ammonium, and nitrate). Accordingly, the number concentration of CCN
in aged air from the megacity region was higher than in fresh city
outflow ((2.5–9.9) × 103 cm−3 vs.
(0.4–8.3) × 103 cm−3 for S=0.07–0.86%) although the total aerosol
particle number concentration was lower
(1.2 × 104 cm−3 vs.
2.3 × 104 cm−3). A comparison with related studies
suggests that the fresh outflow from Chinese urban centers generally
may contain more, but smaller and less hygroscopic aerosol particles
and thus fewer CCN than the aged outflow from megacity regions. |
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