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| Titel |
The effects of airmass history on new particle formation in the free troposphere: case studies |
| VerfasserIn |
D. R. Benson, Li-Hao Young, Shan-Hu Lee, T. L. Campos, D. C. Rogers, J. Jensen |
| 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 ; 8, no. 12 ; Nr. 8, no. 12 (2008-06-18), S.3015-3024 |
| Datensatznummer |
250006213
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| Publikation (Nr.) |
 copernicus.org/acp-8-3015-2008.pdf |
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| Zusammenfassung |
| Recent aircraft studies showed that new particle formation (NPF) is very
active in the free troposphere. And, these observations lead to a new
question: when does NPF not occur? Here, we provide case studies to show how
different meteorological parameters affect NPF in the upper troposphere,
using the aerosol size distributions measured at latitudes from
18° N–52° N and altitudes up to 14 km during the NSF/NCAR GV Progressive
Science Missions. About 95% of the total samples showed the NPF feature
with median number concentrations of particles with diameters from 4 to 9 nm
(N4–9), 288±199 cm−3, and the total particle number
concentrations with diameters from 4 to 2000 nm (N4–2000), 500±259 cm−3. Surface areas were in general very low in the free
troposphere, 1.58±0.87 μm2 cm−3, which in part
explains the high frequency of NPF measured in this region, but there was no
distinctive difference in surface area for the NPF and non-NPF cases. Our
case studies show that rather airmass history is more important for
nucleation in this region. Weak- or non-events did not display uplifting of
airmasses. On the other hand, strong NPF events were usually associated with
uplifting of airmasses, although there were also NPF cases in which uplift
did not occur, consistent with the previous observations (Young et al.,
2007). NPF tends to easily occur in the free troposphere because of low
surface areas and low temperatures (Carslaw and Kärcher, 2006), but
because of the low aerosol precursors in this region, vertical motion (that
can bring higher concentrations of aerosol precursors from low altitude
source regions to higher altitudes) can play a critical role. Latitude
dependence of new particles also shows higher particle concentrations in the
midlatitude and subtropics tropopause region than in the tropics, consistent
with Hermann et al. (2003). |
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