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| Titel |
Evaluation of the accuracy of analysis tools for atmospheric new particle formation |
| VerfasserIn |
H. Korhonen, S.-L. Sihto, V.-M. Kerminen, K. E. J. Lehtinen |
| 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. 7 ; Nr. 11, no. 7 (2011-04-01), S.3051-3066 |
| Datensatznummer |
250009579
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| Publikation (Nr.) |
 copernicus.org/acp-11-3051-2011.pdf |
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| Zusammenfassung |
| Several mathematical tools have been developed in recent years to analyze
new particle formation rates and to estimate nucleation rates and mechanisms
at sub-3 nm sizes from atmospheric aerosol data. Here we evaluate these
analysis tools using 1239 numerical nucleation events for which the
nucleation mechanism and formation rates were known exactly. The accuracy of
the estimates of particle formation rate at 3 nm (J3) showed
significant sensitivity to the details of the analysis, i.e. form of
equations used and assumptions made about the initial size of nucleating
clusters, with the fraction of events within a factor-of-two accuracy
ranging from 43–97%. In general, the estimates of the actual nucleation
rate at 1.5 nm (J1.5) were less accurate, and even the most accurate
analysis set-up estimated only 59% of the events within a factor of two
of the simulated mean nucleation rate. The J1.5 estimates were
deteriorated mainly by the size dependence of the cluster growth rate below
3 nm, which the analysis tools do not take into account, but also by
possible erroneous assumptions about the initial cluster size. The poor
estimates of J1.5 can lead to large uncertainties in the nucleation
prefactors (i.e. constant P in nucleation equation J1.5 = P ×
[H2SO4]k). Large uncertainties were found also in the
procedures that are used to determine the nucleation mechanism. When applied
to individual events, the analysis tools clearly overestimated the number of
H2SO4 molecules in a critical cluster for most events, and thus
associated them with a wrong nucleation mechanism. However, in some
conditions the number of H2SO4 molecules in a critical cluster was
underestimated. This indicates that analysis of field data that implies a
maximum of 2 H2SO4 molecules in a cluster does not automatically
rule out a higher number of molecules in the actual nucleating cluster. Our
analysis also suggests that combining data from several new particle
formation events to scatter plots of H2SO4 vs formation rates
(J1.5 or J3) and determining the slope of the regression line may
not give reliable information about the nucleation mechanism. Overall, while
the analysis tools for new particle formation are useful for getting
order-of-magnitude estimates of parameters related to atmospheric
nucleation, one should be very cautious in interpreting the results. It is,
for example, possible that the tools may have misdirected our theoretical
understanding of the nucleation mechanism. |
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