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| Titel |
Classifying previously undefined days from eleven years of aerosol-particle-size distribution data from the SMEAR II station, Hyytiälä, Finland |
| VerfasserIn |
S. Buenrostro Mazon, I. Riipinen, D. M. Schultz, M. Valtanen, M. Maso, L. Sogacheva, H. Junninen, T. Nieminen, V.-M. Kerminen, 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 ; 9, no. 2 ; Nr. 9, no. 2 (2009-01-28), S.667-676 |
| Datensatznummer |
250006748
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| Publikation (Nr.) |
 copernicus.org/acp-9-667-2009.pdf |
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| Zusammenfassung |
| Studies of secondary aerosol-particle formation depend on identifying days
in which new particle formation occurs and, by comparing them to days with
no signs of particle formation, identifying the conditions favourable for
formation. Continuous aerosol size distribution data has been collected at
the SMEAR II station in a boreal forest in Hyytiälä, Finland, since
1996, making it the longest time series of aerosol size distributions
available worldwide. In previous studies, the data have been classified as
particle-formation event, nonevent, and undefined days, with almost 40%
of the dataset classified as undefined. In the present study, eleven years
(1996–2006) of undefined days (1630 days) were reanalyzed and subdivided
into three new classes: failed events (37% of all previously undefined
days), ultrafine-mode concentration peaks (34%), and pollution-related
concentration peaks (19%). Unclassified days (10%) comprised the rest
of the previously undefined days. The failed events were further subdivided
into tail events (21%), where a tail of a formation event presumed to be
advected to Hyytiälä from elsewhere, and quasi events (16%) where
new particles appeared at sizes 3–10 nm, but showed unclear growth, the
mode persisted for less than an hour, or both. The ultrafine concentration
peaks days were further subdivided into nucleation-mode peaks (24%) and
Aitken-mode peaks (10%), depending on the size range where the particles
occurred. The mean annual distribution of the failed events has a maximum
during summer, whereas the two peak classes have maxima during winter. The
summer minimum previously found in the seasonal distribution of event days
partially offsets a summer maximum in failed-event days. Daily-mean relative
humidity and condensation sink values are useful in discriminating the new
classes from each other. Specifically, event days had low values of relative
humidity and condensation sink relative to nonevent days. Failed-event days
possessed intermediate condensation sink and relative humidity values,
whereas both ultrafine-mode peaks and, to a greater extent,
pollution-related peaks had high values of both, similar to nonevent days.
Using 96-h back trajectories, particle-size concentrations were plotted as a
function of time the trajectory spent over land. Increases in particle size
and number concentration during failed-event days were similar to that
during the later stages of event days, whereas the particle size and number
concentration for both nonevent and peaks classes did not increase as fast
as for event and failed events days. |
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