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| Titel |
Modeling chemical and aerosol processes in the transition from closed to open cells during VOCALS-REx |
| VerfasserIn |
J. Kazil, H. Wang, G. Feingold, A. D. Clarke, J. R. Snider, A. R. Bandy |
| 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 ; 11, no. 15 ; Nr. 11, no. 15 (2011-08-01), S.7491-7514 |
| Datensatznummer |
250009958
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| Publikation (Nr.) |
 copernicus.org/acp-11-7491-2011.pdf |
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| Zusammenfassung |
| Chemical and aerosol processes in the transition from closed- to open-cell circulation in
the remote, cloudy marine boundary layer are explored. It has previously been shown that
precipitation can initiate a transition from the closed- to the open-cellular state, but
that the boundary layer cannot maintain this open-cell state without a resupply of cloud
condensation nuclei (CCN). Potential sources of CCN include wind-driven production of sea salt
from the ocean, nucleation from the gas phase, and entrainment from the free
troposphere. In order to investigate CCN sources in the marine boundary layer and their
role in supplying new particles, we have coupled in detail chemical, aerosol, and cloud
processes in the WRF/Chem model, and added state-of-the-art representations of sea salt
emissions and aerosol nucleation. We conduct numerical simulations of the marine boundary layer in the transition from a closed- to an
open-cell
state. Results are compared with observations in the Southeast Pacific boundary layer during
the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). The transition
from the closed- to the open-cell state generates conditions that are conducive to
nucleation by forming a cloud-scavenged, ultra-clean layer below the inversion base. Open
cell updrafts loft dimethyl sulfide from the ocean surface into the ultra-clean layer,
where it is oxidized during daytime to SO2 and subsequently to H2SO4. Low
H2SO4 condensation sink values in the ultra-clean layer allow H2SO4 to
rise to concentrations at which aerosol nucleation produces new aerosol in significant numbers. The existence of
the ultra-clean layer is confirmed by observations. We find that the observed DMS flux from
the ocean in the VOCALS-REx region can support a nucleation source of aerosol in open cells
that exceeds sea salt emissions in terms of the number of particles produced. The freshly
nucleated, nanometer-sized aerosol particles need, however, time to grow to sizes large enough
to act as CCN. In contrast, mechanical production of particles from the ocean surface by
near-surface winds provides a steady source of larger particles that are effective CCN at
a rate exceeding a threshold for maintenance of open-cell circulation. Entrainment of aerosol
from the free troposphere contributes significantly to boundary layer aerosol for the
considered VOCALS-REx case, but less than sea salt aerosol emissions. |
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