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| Titel |
Seasonal variation of aerosol size distributions in the free troposphere and residual layer at the puy de Dôme station, France |
| VerfasserIn |
H. Venzac, K. Sellegri, P. Villani, D. Picard, P. Laj |
| 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. 4 ; Nr. 9, no. 4 (2009-02-23), S.1465-1478 |
| Datensatznummer |
250006938
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| Publikation (Nr.) |
 copernicus.org/acp-9-1465-2009.pdf |
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| Zusammenfassung |
| Particle number concentration and size distribution are important variables
needed to constrain the role of atmospheric particles in the Earth radiation
budget, both directly and indirectly through CCN activation. They are also
linked to regulated variables such as particle mass (PM) and therefore of
interest to air quality studies. However, data on their long-term
variability are scarce, in particular at high altitudes. In this paper, we
investigate the diurnal and seasonal variability of the aerosol total number
concentration and size distribution at the puy de Dôme research station
(France, 1465 m a.s.l.). We report a variability of aerosol particle total
number concentration measured over a five-year (2003–2007) period for
particles larger than 10 nm and aerosol size distributions between 10 and
500 nm over a two-year period (January 2006 to December 2007).
Concentrations show a strong seasonality with maxima during summer and
minima during winter. A diurnal variation is also observed with maxima
between 12:00 and 18:00 UTC. At night (00:00–06:00 UTC), the median hourly
total concentration varies from 600 to 800 cm−3 during winter and from
1700 to 2200 cm−3 during summer. During the day (08:00–18:00 UTC), the
concentration is in the range of 700 to 1400 cm−3 during winter and of
2500 to 3500 cm−3 during summer. An averaged size distribution of
particles (10–500 nm) was calculated for each season. The total aerosol
number concentrations are dominated by the Aitken mode integral
concentrations, which drive most of the winter to summer total
concentrations increase. The night to day increase in dominated by the
nucleation mode integral number concentration. Because the site is located
in the free troposphere only a fraction of the time, in particular at night
and during the winter season, we have subsequently analyzed the variability
for nighttime and free tropospheric (FT)/residual layer (RL) conditions
only. We show that a seasonal variability is still observed for these FT/RL
conditions. The FT/RL seasonal variation is due to both seasonal changes in
the air mass origin from winter to summer and enhanced concentrations of
particles in the residual layer/free troposphere in summer. The later
observation can be explained by higher emissions intensity in the boundary
layer, stronger exchanges between the boundary layer and the free
troposphere as well as enhanced photochemical processes. Finally, aerosols
mean size distributions are calculated for a given air mass type
(marine/continental/regional) according to the season for the specific
conditions of the residual layer/free troposphere. The seasonal variability
in aerosol sources seems to be predominant over the continent compared to
the seasonal variation of marine aerosol sources. These results are of
regional relevance and can be used to constrain chemical-transport models
over Western Europe. |
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