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| Titel |
Assessment of atmospheric processes driving ozone variations in the subtropical North Atlantic free troposphere |
| VerfasserIn |
E. Cuevas, Y. González, S. Rodríguez, J. C. Guerra, A. J. Gómez-Peláez, S. Alonso-Pérez, J. Bustos, C. Milford |
| 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 ; 13, no. 4 ; Nr. 13, no. 4 (2013-02-20), S.1973-1998 |
| Datensatznummer |
250017671
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| Publikation (Nr.) |
 copernicus.org/acp-13-1973-2013.pdf |
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| Zusammenfassung |
| An analysis of the 22-yr ozone (O3) series (1988–2009) at the
subtropical high mountain Izaña~station (IZO; 2373 m
a.s.l.), representative of free troposphere (FT) conditions, is
presented. Diurnal and seasonal O3 variations as well as the
O3 trend (0.19 ± 0.05 % yr−1 or 0.09 ppbv yr−1), are
assessed. A climatology of O3 transport pathways using
backward trajectories shows that higher O3 values are
associated with air masses travelling above 4 km altitude from North
America and North Atlantic Ocean, while low O3 is transported
from the Saharan continental boundary layer (CBL). O3 data
have been compared with PM10, 210Pb, 7Be,
potential vorticity (PV) and carbon monoxide (CO). A clear negative
logarithmic relationship was observed between PM10 and
surface O3 for all seasons. A similar relationship was found
between O3 and 210Pb. The highest daily O3 values (90th
percentile) are observed in spring and in the first half of
summer time. A positive correlation between O3 and PV, and
between O3 and 7Be is found throughout the year,
indicating that relatively high surface O3 values at IZO
originate from the middle and upper troposphere. We find a good
correlation between O3 and CO in winter, supporting the
hypothesis of long-range transport of photochemically generated
O3 from North America. Aged air masses, in combination with
sporadic inputs from the upper troposphere, are observed in spring,
summer and autumn. In summer time high O3 values seem to be
the result of stratosphere-to-troposphere (STT) exchange processes in
regions neighbouring the Canary Islands. Since 1995–1996, the North
Atlantic Oscillation has changed from a predominantly high positive
phase to alternating between negative, neutral or positive
phases. This change results in an increased flow of the westerlies in
the mid-latitude and subtropical North Atlantic, thus favouring the
transport of O3 and its precursors from North America, and
a higher frequency of storms over North Atlantic, with a likely higher
incidence of STT processes in mid-latitudes. These processes lead to
an increase of tropospheric O3 in the subtropical North
Atlantic region after 1996 that has been reflected in surface
O3 records at IZO. |
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