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| Titel |
Variability of air ion concentrations in urban Paris |
| VerfasserIn |
V. N. Dos Santos, E. Herrmann, H. E. Manninen, T. Hussein, J. Hakala, T. Nieminen, P. P. Aalto, M. Merkel, A. Wiedensohler, M. Kulmala  , T. Petäjä, K. Hämeri |
| 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. 23 ; Nr. 15, no. 23 (2015-12-14), S.13717-13737 |
| Datensatznummer |
250120221
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| Publikation (Nr.) |
 copernicus.org/acp-15-13717-2015.pdf |
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| Zusammenfassung |
| Air ion concentrations influence new particle formation and
consequently the global aerosol as potential cloud condensation nuclei. We
aimed to evaluate air ion concentrations and characteristics of new particle
formation events (NPF) in the megacity of Paris, France, within the MEGAPOLI
(Megacities: Emissions, urban, regional and Global Atmospheric
Pollution and climate effects, and Integrated tools for assessment and
mitigation) project. We measured air ion number size distributions (0.8–42 nm) with an
air ion spectrometer and fine particle number concentrations (> 6 nm) with a twin differential mobility particle sizer in an urban site of
Paris between 26 June 2009 and 4 October 2010. Air ions were size classified
as small (0.8–2 nm), intermediate (2–7 nm), and large (7–20 nm). The
median concentrations of small and large ions were 670 and 680 cm−3,
respectively, (sum of positive and negative polarities), whereas the median
concentration of intermediate ions was only 20 cm−3, as these ions were
mostly present during new particle formation bursts, i.e. when
gas-to-particle conversion produced fresh aerosol particles from gas phase
precursors. During peaks in traffic-related particle number, the
concentrations of small and intermediate ions decreased, whereas the
concentrations of large ions increased. Seasonal variations affected the ion
population differently, with respect to their size and polarity. NPF was
observed in 13 % of the days, being most frequent in spring and late
summer (April, May, July, and August). The results also suggest that NPF was
favoured on the weekends in comparison to workdays, likely due to the lower
levels of condensation sinks in the mornings of weekends (CS weekdays 09:00:
18 × 10−3 s−1; CS weekend 09:00: 8 × 10−3 s−1). The median growth rates (GR) of ions during the NPF events varied
between 3 and 7 nm h−1, increasing with the ion size and being higher on
workdays than on weekends for intermediate and large ions. The median GR of
small ions on the other hand were rather similar on workdays and weekends.
In general, NPF bursts changed the diurnal cycle of particle number as well
as intermediate and large ions by causing an extra peak between 09:00 and
14:00. On average, during the NPF bursts the concentrations of intermediate
ions were 8.5–10 times higher than on NPF non-event days, depending on the
polarity, and the concentrations of large ions and particles were 1.5–1.8
and 1.2 times higher, respectively. Because the median concentrations of
intermediate ions were considerably higher on NPF event days in comparison
to NPF non-event days, the results indicate that intermediate ion
concentrations could be used as an indication for NPF in Paris. The results
suggest that NPF was a source of ions and aerosol particles in Paris and
therefore contributed to both air quality degradation and climatic effects,
especially in the spring and summer. |
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