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| Titel |
On the competition among aerosol number, size and composition in predicting CCN variability: a multi-annual field study in an urbanized desert |
| VerfasserIn |
E. Crosbie, J.-S. Youn, B. Balch, A. Wonaschütz, T. Shingler, Z. Wang, W. C. Conant, E. A. Betterton, A. Sorooshian |
| 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 ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-25), S.6943-6958 |
| Datensatznummer |
250119851
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| Publikation (Nr.) |
 copernicus.org/acp-15-6943-2015.pdf |
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| Zusammenfassung |
A 2-year data set of measured CCN (cloud condensation nuclei) concentrations
at 0.2 % supersaturation is combined with aerosol size distribution and
aerosol composition data to probe the effects of aerosol number
concentrations, size distribution and composition on CCN patterns. Data were
collected over a period of 2 years (2012–2014) in central Tucson, Arizona: a
significant urban area surrounded by a sparsely populated desert. Average CCN
concentrations are typically lowest in spring (233 cm−3), highest in
winter (430 cm−3) and have a secondary peak during the North American
monsoon season (July to September; 372 cm−3). There is significant
variability outside of seasonal patterns, with extreme concentrations (1 and
99 % levels) ranging from 56 to 1945 cm−3 as measured during the
winter, the season with highest variability.
Modeled CCN concentrations based on fixed chemical composition achieve better
closure in winter, with size and number alone able to predict 82 % of the
variance in CCN concentration. Changes in aerosol chemical composition are
typically aligned with changes in size and aerosol number, such that
hygroscopicity can be parameterized even though it is still variable. In
summer, models based on fixed chemical composition explain at best only
41 % (pre-monsoon) and 36 % (monsoon) of the variance. This is
attributed to the effects of secondary organic aerosol (SOA) production, the
competition between new particle formation and condensational growth, the
complex interaction of meteorology, regional and local emissions and
multi-phase chemistry during the North American monsoon. Chemical composition
is found to be an important factor for improving predictability in spring and
on longer timescales in winter.
Parameterized models typically exhibit improved predictive skill when there
are strong relationships between CCN concentrations and the prevailing
meteorology and dominant aerosol physicochemical processes, suggesting that
similar findings could be possible in other locations with comparable
climates and geography. |
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