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| Titel |
Estimation of cloud condensation nuclei concentration from aerosol optical quantities: influential factors and uncertainties |
| VerfasserIn |
Jianjun Liu, Zhanqing Li |
| 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. 1 ; Nr. 14, no. 1 (2014-01-15), S.471-483 |
| Datensatznummer |
250118264
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| Publikation (Nr.) |
 copernicus.org/acp-14-471-2014.pdf |
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| Zusammenfassung |
| Large-scale measurements of cloud condensation nuclei (CCN) are difficult to
obtain on a routine basis, whereas aerosol optical quantities are more
readily available. This study investigates the relationship between CCN and
aerosol optical quantities for some distinct aerosol types using extensive
observational data collected at multiple Atmospheric Radiation Measurement
(ARM) Climate Research Facility (CRF) sites around the world. The influences
of relative humidity (RH), aerosol hygroscopicity (fRH) and single
scattering albedo (SSA) on the relationship are analyzed. Better
relationships are found between aerosol optical depth (AOD) and CCN at the
Southern Great Plains (US), Ganges Valley (India) and Black Forest sites
(Germany) than those at the Graciosa Island (the Azores) and Niamey (Niger)
sites, where sea salt and dust aerosols dominate, respectively. In general,
the correlation between AOD and CCN decreases as the wavelength of the AOD
measurement increases, suggesting that AOD at a shorter wavelength is a
better proxy for CCN. The correlation is significantly improved if aerosol
index (AI) is used together with AOD. The highest correlation exists between
CCN and aerosol scattering coefficients (σsp) and scattering AI
measured in situ. The CCN–AOD (AI) relationship deteriorates with increasing
RH. If RH exceeds 75%, the relationship where AOD is used as a proxy for
CCN becomes invalid, whereas a tight σsp–CCN relationship
exists for dry particles. Aerosol hygroscopicity has a weak impact on the
σsp–CCN relationship. Particles with low SSA are generally
associated with higher CCN concentrations, suggesting that SSA affects the
relationship between CCN concentration and aerosol optical quantities. It
may thus be used as a constraint to reduce uncertainties in the
relationship. A significant increase in σsp and decrease in CCN
with increasing SSA is observed, leading to a significant decrease in their
ratio (CCN / σsp) with increasing SSA. Parameterized
relationships are developed for estimating CCN, which account for RH,
particle size, and SSA. |
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