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| Titel |
Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site |
| VerfasserIn |
J. C. Schroder, S. J. Hanna, R. L. Modini, A. L. Corrigan, S. M. Kreidenwies, A. M. Macdonald, K. J. Noone, L. M. Russell, W. R. Leaitch, A. K. Bertram |
| 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. 3 ; Nr. 15, no. 3 (2015-02-09), S.1367-1383 |
| Datensatznummer |
250119396
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| Publikation (Nr.) |
 copernicus.org/acp-15-1367-2015.pdf |
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| Zusammenfassung |
| Size-resolved observations of aerosol particles and cloud droplet residuals
were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A counterflow virtual impactor (CVI) was used as the inlet to
sample cloud residuals while a total inlet was used to sample both cloud
residuals and interstitial particles. Two cloud events totaling 10 h of
in-cloud sampling were analyzed. Based on bulk aerosol particle
concentrations, mass concentrations of refractory black carbon (rBC), and
back trajectories, the two air masses sampled were classified as polluted
marine air. Since the fraction of cloud droplets sampled by the CVI was less
than 100%, the measured activated fractions of rBC should be considered
as lower limits to the total fraction of rBC activated during the two cloud
events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud
droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least
65 nm were incorporated into the cloud droplets). Measurements also show
that the coating volume fraction of rBC cores is relatively large for
sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result
that is consistent with κ-Köhler theory. Measurements of the total
diameter of the rBC-containing particles (rBC core and coating) suggest that
the total diameter of rBC-containing particles needed to be at least 165 nm
to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that
particle diameter is important for activation of non-rBC particles. The
activated fractions of rBC determined from the measurements ranged from
0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of
data is useful for constraining models used for predicting rBC
concentrations in the atmosphere. |
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