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| Titel |
Lightning-produced NOx over Brazil during TROCCINOX: airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems |
| VerfasserIn |
H. Huntrieser, H. Schlager, A. Roiger, M. Lichtenstern, U. Schumann, C. Kurz, D. Brunner, C. Schwierz, A. Richter, A. Stohl |
| 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. 11 ; Nr. 7, no. 11 (2007-06-12), S.2987-3013 |
| Datensatznummer |
250005043
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| Publikation (Nr.) |
 copernicus.org/acp-7-2987-2007.pdf |
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| Zusammenfassung |
| During the TROCCINOX field experiments in February–March 2004 and February
2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing
ratios and the J(NO2) photolysis rate were carried out in the anvil
outflow of thunderstorms over southern Brazil. Both tropical and subtropical
thunderstorms were investigated, depending on the location of the South
Atlantic convergence zone. Tropical air masses were discriminated from
subtropical ones according to the higher equivalent potential temperature
(Θe) in the lower and mid troposphere, the higher CO mixing
ratio in the mid troposphere, and the lower wind velocity in the upper troposphere
within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations,
typically at 20–40 km horizontal scales, NOx mixing ratios were distinctly enhanced and the absolute mixing ratios
varied between 0.2–1.6 nmol mol−1 on average. This enhancement was mainly
attributed to NOx production by lightning and partly due to upward
transport from the NOx-richer boundary layer. In addition, CO mixing
ratios were occasionally enhanced, indicating upward transport from the
boundary layer. For the first time, the composition of the anvil outflow
from a large, long-lived mesoscale convective system (MCS) advected from
northern Argentina and Uruguay was investigated in more detail. Over a
horizontal scale of about 400 km, NOx, CO and O3 absolute mixing ratios
were significantly enhanced in these air masses in the range of 0.6–1.1,
110–140 and 60–70 nmol mol−1, respectively. Analyses from trace gas
correlations and a Lagrangian particle dispersion model indicate that
polluted air masses, probably from the Buenos Aires urban area and from
biomass burning regions, were uplifted by the MCS. Ozone was distinctly
enhanced in the aged MCS outflow, due to photochemical production and
entrainment of O3-rich air masses from the upper troposphere – lower
stratosphere region. The aged MCS outflow was transported to the north,
ascended and circulated, driven by the Bolivian High over the Amazon basin.
In the observed case, the O3-rich MCS outflow remained over the
continent and did not contribute to the South Atlantic ozone maximum. |
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