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| Titel |
Aircraft measurements over Europe of an air pollution plume from Southeast Asia – aerosol and chemical characterization |
| VerfasserIn |
A. Stohl, C. Forster, H. Huntrieser, H. Mannstein, W. W. McMillan, A. Petzold, H. Schlager, B. Weinzierl |
| 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 ; 7, no. 3 ; Nr. 7, no. 3 (2007-02-16), S.913-937 |
| Datensatznummer |
250004572
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| Publikation (Nr.) |
 copernicus.org/acp-7-913-2007.pdf |
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| Zusammenfassung |
| An air pollution plume from Southern and Eastern Asia, including regions in
India and China, was predicted by the FLEXPART particle dispersion model to
arrive in the upper troposphere over Europe on 24–25 March 2006. According to
the model, the plume was exported from Southeast Asia six days earlier,
transported into the upper troposphere by a warm conveyor belt, and travelled
to Europe in a fast zonal flow. This is confirmed by the retrievals of carbon
monoxide (CO) from AIRS satellite measurements, which are in excellent
agreement with the model results over the entire transport history. The
research aircraft DLR Falcon was sent into this plume west of Spain on 24
March and over Southern Europe on 25 March. On both days, the pollution plume
was found close to the predicted locations and, thus, the measurements taken
allowed the first detailed characterization of the aerosol content and
chemical composition of an anthropogenic pollution plume after a nearly
hemispheric transport event. The mixing ratios of CO, reactive nitrogen
(NOy) and ozone (O3) measured in the Asian plume were all clearly
elevated over a background that was itself likely elevated by Asian
emissions: CO by 17–34 ppbv on average (maximum 60 ppbv) and O3 by
2–9 ppbv (maximum 22 ppbv). Positive correlations existed between these
species, and a ΔO3/ΔCO slope of 0.25 shows that ozone was
formed in this plume, albeit with moderate efficiency. Nucleation mode and
Aitken particles were suppressed in the Asian plume, whereas accumulation
mode aerosols were strongly elevated and correlated with CO. The suppression
of the nucleation mode was likely due to the large pre-existing aerosol
surface of the transported larger particles. Super-micron particles, likely
desert dust, were found in part of the Asian pollution plume and also in
surrounding cleaner air. The aerosol light absorption coefficient was
enhanced in the plume (average values for individual plume encounters
0.25–0.70 Mm−1), as was the fraction of non-volatile Aitken particles.
This indicates that black carbon (BC) was an important aerosol component.
During the flight on 25 March, which took place on the rear of a trough
located over Europe, a mixture of Asian pollution and stratospheric air was
found. Asian pollution was mixing into the lower stratosphere, and
stratospheric air was mixing into the pollution plume in the troposphere.
Turbulence was encountered by the aircraft in the mixing regions, where the
thermal stability was low and Richardson numbers were below 0.2. The result
of the mixing can clearly be seen in the trace gas data, which are following
mixing lines in correlation plots. This mixing with stratospheric air is
likely very typical of Asian air pollution, which is often lifted to the
upper troposphere and, thus, transported in the vicinity of stratospheric
air. |
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