 |
| Titel |
Cloud condensation nuclei closure study on summer arctic aerosol |
| VerfasserIn |
M. Martin, R. Y.-W. Chang, B. Sierau, S. Sjogren, E. Swietlicki, J. P. D. Abbatt, C. Leck, U. Lohmann |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 22 ; Nr. 11, no. 22 (2011-11-16), S.11335-11350 |
| Datensatznummer |
250010190
|
| Publikation (Nr.) |
 copernicus.org/acp-11-11335-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
We present an aerosol – cloud condensation nuclei (CCN) closure study
on summer high Arctic aerosol based on measurements that were carried out in
2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish
ice breaker Oden. The data presented here were collected during a
three-week time period in the pack ice (>85° N) when the
icebreaker Oden was moored to an ice floe and drifted passively
during the most biological active period into autumn freeze up conditions.
CCN number concentrations were obtained using two CCN counters
measuring at different supersaturations. The directly measured CCN
number concentration was then compared with a CCN number concentration
calculated using both bulk aerosol mass composition data from an aerosol mass
spectrometer (AMS) and aerosol number size distributions obtained from a
differential mobility particle sizer, assuming κ-Köhler theory,
surface tension of water and an internally mixed aerosol. The last assumption
was supported by measurements made with a hygroscopic tandem differential
mobility analyzer (HTDMA) for particles >70 nm.
For the two highest measured supersaturations, 0.73 and 0.41%, closure
could not be achieved with the investigated settings concerning
hygroscopicity and density. The calculated CCN number concentration was
always higher than the measured one for those two supersaturations. This
might be caused by a relative larger insoluble organic mass fraction of the
smaller particles that activate at these supersaturations, which are thus
less good CCN than the larger particles. On average, 36% of the mass
measured with the AMS was organic mass. At 0.20, 0.15 and 0.10%
supersaturation, closure could be achieved with different combinations of
hygroscopic parameters and densities within the uncertainty range of the fit.
The best agreement of the calculated CCN number concentration with the
observed one was achieved when the organic fraction of the aerosol was
treated as nearly water insoluble (κorg=0.02), leading to a
mean total κ, κtot, of 0.33 ± 0.13. However, several
settings led to closure and κorg=0.2 is found to be an upper
limit at 0.1% supersaturation. κorg≤0.2 leads to a
κtot range of 0.33 ± 013 to 0.50 ± 0.11. Thus, the organic
material ranges from being sparingly soluble to effectively insoluble. These
results suggest that an increase in organic mass fraction in particles of a
certain size would lead to a suppression of the Arctic CCN activity. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|