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| Titel |
Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| VerfasserIn |
A. M. Thompson, N. V. Balashov, J. C. Witte, J. G. R. Coetzee, V. Thouret, F. Posny |
| 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. 18 ; Nr. 14, no. 18 (2014-09-17), S.9855-9869 |
| Datensatznummer |
250119044
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| Publikation (Nr.) |
 copernicus.org/acp-14-9855-2014.pdf |
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| Zusammenfassung |
| Increases in free-tropospheric (FT) ozone based on ozonesonde records from
the early 1990s through 2008 over two subtropical stations, Irene (near
Pretoria, South Africa) and Réunion (21° S, 55° E;
~2800 km NE of Irene in the Indian Ocean), have been reported. Over
Irene a large increase in the urban-influenced boundary layer (BL, 1.5–4 km)
was also observed during the 18-year period, equivalent to
30% decade−1. Here we show that the Irene BL trend is at least
partly due to a gradual change in the sonde launch times from early morning
to the midday period. The FT ozone profiles over Irene in 1990–2007 are
re-examined, filling in a 1995–1999 gap with ozone profiles taken during the
Measurements of Ozone by Airbus In-service Aircraft (MOZAIC) project over
nearby Johannesburg. A multivariate regression model that accounts for the
annual ozone cycle, El Niño–Southern Oscillation (ENSO) and possible
tropopause changes was applied to monthly averaged Irene data from 4 to
11 km and to 1992–2011 Réunion sonde data from 4 to 15 km.
Statistically significant trends appear predominantly in the middle and upper
troposphere (UT; 4–11 km over Irene, 4–15 km over Réunion) in winter
(June–August), with increases ~1 ppbv yr−1 over Irene and
~2 ppbv yr−1 over Réunion. These changes are equivalent to
~25 and 35–45% decade−1, respectively. Both stations also
display smaller positive trends in summer, with a 45% decade−1
ozone increase near the tropopause over Réunion in December. To explain
the ozone increases, we investigated a time series of dynamical markers,
e.g., potential vorticity (PV) at 330–350 K. PV affects UT ozone over Irene
in November–December but displays little relationship with ozone over
Réunion. A more likely reason for wintertime FT ozone increases over
Irene and Réunion appears to be long-range transport of growing pollution
in the Southern Hemisphere. The ozone increases are consistent with
trajectory origins of air parcels sampled by the sondes and with recent
NOx emissions trends estimated for Africa, South America and
Madagascar. For Réunion trajectories also point to sources from the
eastern Indian Ocean and Asia. |
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