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| Titel |
Total sulfate vs. sulfuric acid monomer concenterations in nucleation studies |
| VerfasserIn |
K. Neitola, D. Brus, U. Makkonen, M. Sipilä, R. L. Mauldin III, N. Sarnela, T. Jokinen, H. Lihavainen, M. Kulmala  |
| 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 ; 15, no. 6 ; Nr. 15, no. 6 (2015-03-28), S.3429-3443 |
| Datensatznummer |
250119581
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| Publikation (Nr.) |
 copernicus.org/acp-15-3429-2015.pdf |
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| Zusammenfassung |
| Sulfuric acid is known to be a key component for atmospheric nucleation.
Precise determination of sulfuric-acid concentration is a crucial factor for
prediction of nucleation rates and subsequent growth. In our study, we have
noticed a substantial discrepancy between sulfuric-acid monomer
concentrations and total-sulfate concentrations measured from the same source
of sulfuric-acid vapor. The discrepancy of about 1–2 orders of magnitude was
found with similar particle-formation rates. To investigate this discrepancy,
and its effect on nucleation, a method of thermally controlled saturator
filled with pure sulfuric acid (97% wt.) for production of
sulfuric-acid vapor is applied and rigorously tested. The saturator provided
an independent vapor-production method, compared to our previous method of
the furnace (Brus et al., 2010, 2011), to find out if the discrepancy is
caused by the production method itself. The saturator was used in a
H2SO4–H2O nucleation experiment, using a laminar flow tube to
check reproducibility of the nucleation results with the saturator method,
compared to the furnace. Two independent methods of mass spectrometry and
online ion chromatography were used for detecting sulfuric-acid or sulfate
concentrations. Measured sulfuric-acid or total-sulfate concentrations are
compared to theoretical predictions calculated using vapor pressure and a
mixing law. The calculated prediction of sulfuric-acid concentrations agrees
very well with the measured values when total sulfate is considered.
Sulfuric-acid monomer concentration was found to be about 2 orders of
magnitude lower than theoretical predictions, but with a temperature
dependency similar to the predictions and the results obtained with the
ion-chromatograph method. Formation rates are reproducible when compared to
our previous results with both sulfuric-acid or total-sulfate detection and
sulfuric-acid production methods separately, removing any doubts that the
vapor-production method would cause the discrepancy. Possible reasons for the
discrepancy are discussed and some suggestions include that the missing
sulfuric acid is in clusters, formed with contaminants found in most
laboratory experiments. One-to-two-order-of-magnitude higher sulfuric-acid
concentrations (measured as total sulfate in this study) would contribute to
a higher fraction of particle growth rate than assumed from the measurements
by mass spectrometers (i.e. sulfuric-acid monomer). However, the observed
growth rates by sulfate-containing vapor in this study does not directly
imply a similar situation in the field, where sources of sulfate are much
more diverse. |
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