 |
| Titel |
How quickly do cloud droplets form on atmospheric particles? |
| VerfasserIn |
C. R. Ruehl, P. Y. Chuang, A. Nenes |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 4 ; Nr. 8, no. 4 (2008-02-27), S.1043-1055 |
| Datensatznummer |
250005682
|
| Publikation (Nr.) |
 copernicus.org/acp-8-1043-2008.pdf |
|
|
|
|
|
| Zusammenfassung |
| The influence of aerosols on cloud properties is an important modulator of
the climate system. Traditional Köhler theory predicts the equilibrium
concentration of cloud condensation nuclei (CCN); however, it is not known
to what extent particles exist in the atmosphere that may be prevented from
acting as CCN by kinetic limitations. We measured the rate of cloud droplet
formation on atmospheric particles sampled at four sites across the United
States during the summer of 2006: Great Smoky Mountain National Park, TN;
Bondville, IL; Houston, TX; and the Atmospheric Radiation Measurement
Program Southern Great Plains site near Lamont, OK. We express droplet
growth rates with the mass accommodation coefficient (α), and report values
of α measured in the field normalized to the mean α measured for lab-generated
ammonium sulfate (AS) particles (i.e., α'=α/αAS). Overall, 59% of ambient
CCN grew at a rate similar to AS. We report the fraction of CCN that were
"low-α' " (α'<10−1, corresponding to α<1.5×10−2). Of
the 16 days during which these measurements were made, 8 had relatively few
low-α' CCN (<16%), 6 had moderate low-α' fractions (27% to 59%), and 2
had large low-α' fractions (>82% during at least one
~30 min
period). Day to day variability was greatest in Tennessee and Illinois, and
low-α' particles were most prevalent on days when back trajectories suggested
that air was arriving from aloft. The highest fractions of low-α'
CCN in Houston and Illinois occurred around local noon, and decreased later
in the day. These results suggest that for some air masses, accurate
quantification of CCN concentrations may need to account for kinetic
limitations. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|