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| Titel |
Size-resolved cloud condensation nuclei (CCN) activity and closure analysis at the HKUST Supersite in Hong Kong |
| VerfasserIn |
J. W. Meng, M. C. Yeung, Y. J. Li, B. Y. L. Lee, C. K. Chan |
| 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. 18 ; Nr. 14, no. 18 (2014-09-26), S.10267-10282 |
| Datensatznummer |
250119068
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| Publikation (Nr.) |
 copernicus.org/acp-14-10267-2014.pdf |
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| Zusammenfassung |
The cloud condensation nuclei (CCN) properties of atmospheric aerosols were
measured on 1–30 May 2011 at the HKUST (Hong Kong University of Science and
Technology) Supersite, a coastal site in Hong Kong. Size-resolved CCN
activation curves, the ratio of number concentration of CCN
(NCCN) to aerosol concentration (NCN) as a function
of particle size, were obtained at supersaturation (SS) = 0.15, 0.35,
0.50, and 0.70% using a DMT (Droplet Measurement Technologies) CCN counter
(CCNc) and a TSI scanning mobility particle sizer (SMPS). The mean bulk
size-integrated NCCN ranged from ~500 cm−3 at
SS = 0.15% to ~2100 cm−3 at SS = 0.70%, and
the mean bulk NCCN / NCN ratio ranged from 0.16
at SS = 0.15% to 0.65 at SS = 0.70%. The average critical
mobility diameters (D50) at SS = 0.15, 0.35, 0.50, and 0.70%
were 116, 67, 56, and 46 nm, respectively. The corresponding average
hygroscopic parameters (κCCN) were 0.39, 0.36, 0.31, and
0.28. The decrease in κCCN can be attributed to the increase
in organic to inorganic volume ratio as particle size decreases, as measured
by an Aerodyne high resolution time-of-flight aerosol mass spectrometer
(HR-ToF-AMS). The κCCN correlates reasonably well with
κAMS_SR based on size-resolved AMS measurements:
κAMS_SR = κorg × forg
+ κinorg × finorg, where
forg and finorg are the organic and inorganic volume
fractions, respectively, κorg = 0.1 and
κinorg = 0.6, with a R2 of 0.51.
In closure analysis, NCCN was estimated by integrating the
measured size-resolved NCN for particles larger than D50
derived from κ assuming internal mixing state. Estimates using
κAMS_SR show that the measured and predicted
NCCN were generally within 10% of each other at all four SS.
The deviation increased to 26% when κAMS was calculated
from bulk PM1 AMS measurements of particles because PM1 was dominated
by particles of 200 to 500 nm in diameter, which had a larger inorganic
fraction than those of D50 (particle diameter < 200 nm). A
constant κ = 0.33 (the average value of κAMS_SR
over the course of campaign) was found to give an NCCN prediction
within 12% of the actual measured values. We also compared
NCCN estimates based on the measured average D50 and the
average size-resolved CCN activation ratio to examine the relative importance
of hygroscopicity and mixing state. NCCN appears to be relatively
more sensitive to the mixing state and hygroscopicity at a high
SS = 0.70% and a low SS = 0.15%, respectively. |
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