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| Titel |
CCN activity of organic aerosols observed downwind of urban emissions during CARES |
| VerfasserIn |
F. Mei, A. Setyan, Q. Zhang, J. Wang |
| 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 ; 13, no. 24 ; Nr. 13, no. 24 (2013-12-17), S.12155-12169 |
| Datensatznummer |
250085881
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| Publikation (Nr.) |
 copernicus.org/acp-13-12155-2013.pdf |
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| Zusammenfassung |
| During the Carbonaceous Aerosols and Radiative Effects Study (CARES),
activation fraction of size-resolved aerosol particles and aerosol chemical
composition were characterized at the T1 site (~60 km
downwind of Sacramento, California) from 10 June to 28 June 2010. The
hygroscopicity of cloud condensation nuclei (CCN)-active particles (κCCN) with diameter
from 100 to 170 nm, derived from the size-resolved activated fraction,
varied from 0.10 to 0.21, with an average of 0.15, which was substantially
lower than that proposed for continental sites. The low κCCN
value was due to the high organic volume fraction, averaged over 80% at
the T1 site. The derived κCCN exhibited little diurnal
variation, consistent with the relatively constant organic volume fraction
observed. At any time, over 90% of the size-selected particles with
diameter between 100 and 171 nm were CCN active, suggesting most particles
within this size range were aged background particles. Due to the large
organic volume fraction, organic hygroscopicity (κorg) strongly
impacted particle hygroscopicity and therefore calculated CCN concentration.
For the vast majority of the cases, an increase of κorg from
0.03 to 0.18, which are within the typical range, doubled the calculated CCN
concentration. Organic hygroscopicity was derived from κCCN and
aerosol chemical composition, and its variations with the fraction of total
organic mass spectral signal at m / z 44 (f44) and O : C were compared to
results from previous studies. Overall, the relationships between κorg
and f44 are quite consistent for organic aerosol (OA) observed
during field studies and those formed in a smog chamber. Compared to the
relationship between κorg and f44, the relationship between
κorg and O : C exhibits more significant differences among
different studies, suggesting κorg may be better parameterized
using f44. A least squares fit yielded κorg = 2.10(±0.07) × f44 − 0.11(±0.01) with a Pearson
R2 value of 0.71. One possible explanation for the stronger correlation
between κorg and f44 is that the m / z 44 signal (mostly
contributed by the CO2+ ion) is more closely related to organic
acids, which may dominate the overall κorg due to their
relatively high water solubility and hygroscopicity. |
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