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| Titel |
Droplet activation, separation, and compositional analysis: laboratory studies and atmospheric measurements |
| VerfasserIn |
N. Hiranuma, M. Kohn, M. S. Pekour, D. A. Nelson, J. E. Shilling, D. J. Cziczo |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 10 ; Nr. 4, no. 10 (2011-10-26), S.2333-2343 |
| Datensatznummer |
250002127
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| Publikation (Nr.) |
 copernicus.org/amt-4-2333-2011.pdf |
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| Zusammenfassung |
| Droplets produced in a cloud condensation nuclei chamber (CCNC) as a
function of supersaturation have been separated from unactivated aerosol
particles using counterflow virtual impaction. Residual material after
droplets were evaporated was chemically analyzed with an Aerodyne Aerosol
Mass Spectrometer (AMS) and the Particle Analysis by Laser Mass Spectrometry
(PALMS) instrument. Experiments were initially conducted to verify
activation conditions for monodisperse ammonium sulfate particles and to
determine the resulting droplet size distribution as a function of
supersaturation. Based on the observed droplet size, the counterflow virtual
impactor cut-size was set to differentiate droplets from unactivated
interstitial particles. Validation experiments were then performed to verify
that only droplets with sufficient size passed through the counterflow
virtual impactor for subsequent analysis. A two-component external mixture
of monodisperse particles was also exposed to a supersaturation which would
activate one of the types (hygroscopic salts) but not the other (polystyrene
latex spheres or adipic acid). The mass spectrum observed after separation
indicated only the former, validating separation of droplets from
unactivated particles. Results from ambient measurements using this
technique and AMS analysis were inconclusive, showing little chemical
differentiation between ambient aerosol and activated droplet residuals,
largely due to low signal levels. When employing as single particle mass
spectrometer for compositional analysis, however, we observed enhancement of
sulfate in droplet residuals. |
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