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| Titel |
Growth of sulphuric acid nanoparticles under wet and dry conditions |
| VerfasserIn |
L. Skrabalova, D. Brus, T. Anttila, V. Ždímal, H. Lihavainen |
| 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 ; 14, no. 12 ; Nr. 14, no. 12 (2014-06-27), S.6461-6475 |
| Datensatznummer |
250118844
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| Publikation (Nr.) |
 copernicus.org/acp-14-6461-2014.pdf |
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| Zusammenfassung |
| New particle formation, which greatly influences the number concentrations
and size distributions of an atmospheric aerosol, is often followed by a
rapid growth of freshly formed particles. The initial growth of newly
formed aerosol is the crucial process determining the fraction of nucleated
particles growing to cloud condensation nuclei sizes, which have a
significant influence on climate. In this study, we report the laboratory
observations of the growth of nanoparticles produced by nucleation of
H2SO4 and water in a laminar flow tube at temperatures of 283, 293
and 303 K, under dry (a relative humidity of 1%) and wet conditions
(relative humidity of 30%) and residence times of 30, 45, 60 and 90 s.
The initial H2SO4 concentration spans the range from 2 × 108
to 1.4 × 1010 molecule cm−3 and the calculated
wall losses of H2SO4 were assumed to be diffusion limited. The
detected particle number concentrations, measured by the Ultrafine
Condensation Particle Counter (UCPC) and Differential Mobility Particle
Sizer (DMPS), were found to depend strongly on the residence time.
Hygroscopic particle growth, presented by growth factors, was found to be in
good agreement with the previously reported studies. The experimental growth
rates ranged from 20 nm h−1 to 890 nm h−1 at relative humidity (RH) 1% and from
7 nm h−1 to 980 nm h−1 at RH 30% and were found to increase
significantly with the increasing concentration of H2SO4.
Increases in the nucleation temperature had a slight enhancing effect on the
growth rates under dry conditions. The influence of relative humidity on
growth was not consistent – at lower H2SO4 concentrations, the
growth rates were higher under dry conditions while at H2SO4
concentrations greater than 1 × 1010 molecule cm−3, the
growth rates were higher under wet conditions. The growth rates show only a
weak dependence on the residence time. The experimental observations were
compared with predictions made using a numerical model, which investigates
the growth of particles with three different extents of neutralization by
ammonia, NH3: (1) pure H2SO4 – H2O particles; (2)
particles formed by ammonium bisulphate, (NH4)HSO4; (3) particles
formed by ammonium sulphate, (NH4)2SO4. The highest growth
rates were found for ammonium sulphate particles. Since the model accounting
for the initial H2SO4 concentration predicted the experimental
growth rates correctly, our results suggest that the commonly presumed
diffusional wall losses of H2SO4 in case of long-lasting
experiments are not so significant. We therefore assume that there are not
only losses of H2SO4 on the wall, but also a flux of
H2SO4 molecules from the wall into the flow tube, the effect being
more profound under dry conditions and at higher temperatures of the tube
wall. Based on a comparison with the atmospheric observations, our results
indicate that sulphuric acid alone cannot explain the growth rates of
particles formed in the atmosphere. |
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