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| Titel |
Aerosol hygroscopicity and cloud condensation nuclei activity during the AC3Exp campaign: implications for cloud condensation nuclei parameterization |
| VerfasserIn |
F. Zhang, Y. Li, Z. Li, L. Sun, R. Li, C. Zhao, P. Wang, Y. Sun, X. Liu, J. Li, P. Li, G. Ren, T. Fan |
| 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 ; 14, no. 24 ; Nr. 14, no. 24 (2014-12-16), S.13423-13437 |
| Datensatznummer |
250119246
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| Publikation (Nr.) |
 copernicus.org/acp-14-13423-2014.pdf |
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| Zusammenfassung |
| Aerosol hygroscopicity and cloud condensation nuclei (CCN) activity under
background conditions and during pollution events are investigated during the
Aerosol-CCN-Cloud Closure Experiment (AC3Exp) campaign conducted at
Xianghe, China in summer 2013. A gradual increase in size-resolved
activation ratio (AR) with particle diameter (Dp) suggests that aerosol
particles have different hygroscopicities. During pollution events, the
activation diameter (Da) measured at low supersaturation (SS) was
significantly increased compared to background conditions. An increase was
not observed when SS was > 0.4%. The hygroscopicity parameter
(κ) was ~ 0.31–0.38 for particles in
accumulation mode under background conditions. This range in magnitude of
κ was ~ 20%, higher than κ derived under
polluted conditions. For particles in nucleation or Aitken mode, κ
ranged from 0.20–0.34 for background and polluted cases. Larger particles
were on average more hygroscopic than smaller particles. The situation was
more complex for heavy pollution particles because of the diversity in
particle composition and mixing state. A non-parallel observation CCN
closure test showed that uncertainties in CCN number concentration estimates
ranged from 30–40%, which are associated with changes in particle
composition as well as measurement uncertainties associated with bulk and
size-resolved CCN methods. A case study showed that bulk CCN activation
ratios increased as total condensation nuclei (CN) number concentrations
(NCN) increased on background days. The background case also showed
that bulk AR correlated well with the hygroscopicity parameter calculated
from chemical volume fractions. On the contrary, bulk AR decreased with
increasing total NCN during pollution events, but was closely related to
the fraction of the total organic mass signal at m/z 44 (f44), which is usually associated with the particle's organic oxidation level. Our study highlights the importance of chemical composition in
determining particle activation properties and underlines the significance
of long-term observations of CCN under different atmospheric environments,
especially regions with heavy pollution. |
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