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| Titel |
Analysis of cloud condensation nuclei composition and growth kinetics using a pumped counterflow virtual impactor and aerosol mass spectrometer |
| VerfasserIn |
J. G. Slowik, D. J. Cziczo, J. P. D. Abbatt |
| 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. 8 ; Nr. 4, no. 8 (2011-08-30), S.1677-1688 |
| Datensatznummer |
250002083
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| Publikation (Nr.) |
 copernicus.org/amt-4-1677-2011.pdf |
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| Zusammenfassung |
| We present a new method of determining the size and composition of
CCN-active aerosol particles. Method utility is illustrated through a series
of ambient measurements. A continuous-flow thermal-gradient diffusion
chamber (TGDC), pumped counterflow virtual impactor (PCVI), and Aerodyne
time-of-flight mass spectrometer (AMS) are operated in series. Ambient
particles are sampled into the TGDC, where a constant supersaturation is
maintained, and CCN-active particles grow to ~2.5 ± 0.5 μm.
The output flow from the TGDC is directed into the PCVI, where a counterflow
of dry N2 gas opposes the particle-laden flow, creating a region of
zero axial velocity. This stagnation plane can only be traversed by particles with
sufficient momentum, which depends on their size. Particles that have
activated in the TGDC cross the stagnation plane and are entrained in the
PCVI output flow, while the unactivated particles are diverted to a pump.
Because the input gas is replaced by the counterflow gas with better than
99 % efficiency at the stagnation plane, the output flow consists almost
entirely of dry N2 and water evaporates from the activated particles.
In this way, the system yields an ensemble of CCN-active particles whose
chemical composition and size are analyzed using the AMS. Measurements of
urban aerosol in downtown Toronto identified an external mixture of
CCN-active particles consisting almost entirely of ammonium nitrate and
ammonium sulfate, with CCN-inactive particles of the same size consisting of
a mixture of ammonium nitrate, ammonium sulfate, and organics. We also
discuss results from the first field deployment of the TGDC-PCVI-AMS system,
conducted from mid-May to mid-June 2007 in Egbert, Ontario, a
semirural site ~80 km north of Toronto influenced both by clean air
masses from the north and emissions from the city. Organic-dominated
particles sampled during a major biogenic event exhibited higher CCN
activity and/or faster growth kinetics than urban outflow from Toronto,
despite the latter having a higher inorganic content and higher O:C ratio.
During both events, particles were largely internally mixed. |
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