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| Titel |
Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons |
| VerfasserIn |
P. B. Voss, R. A. Zaveri, F. M. Flocke, H. Mao, T. P. Hartley, P. DeAmicis, I. Deonandan, G. Contreras-Jiménez, O. Martínez-Antonio, M. Figueroa Estrada, D. Greenberg, T. L. Campos, A. J. Weinheimer, D. J. Knapp, D. D. Montzka, J. D. Crounse, P. O. Wennberg, E. Apel, S. Madronich, B. Foy |
| 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 ; 10, no. 15 ; Nr. 10, no. 15 (2010-08-04), S.7137-7159 |
| Datensatznummer |
250008676
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| Publikation (Nr.) |
 copernicus.org/acp-10-7137-2010.pdf |
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| Zusammenfassung |
| One of the major objectives of the Megacities Initiative: Local And Global
Research Observations (MILAGRO-2006) campaign was to investigate the
long-range transport of polluted Mexico City Metropolitan Area (MCMA)
outflow and determine its downwind impacts on air quality and climate. Six
research aircraft, including the National Center for Atmospheric Research
(NCAR) C-130, made extensive chemical, aerosol, and radiation measurements
above MCMA and more than 1000 km downwind in order to characterize the
evolution of the outflow as it aged and dispersed over the Mesa Alta, Sierra
Madre Oriental, Coastal Plain, and Gulf of Mexico. As part of this effort,
free-floating Controlled-Meteorological (CMET) balloons, commanded to change
altitude via satellite, made repeated profile measurements of winds and
state variables within the advecting outflow. In this paper, we present an
analysis of the data from two CMET balloons that were launched near Mexico
City on the afternoon of 18 March 2006 and floated downwind with the MCMA
pollution for nearly 30 h. The repeating profile measurements show the
evolving structure of the outflow in considerable detail: its stability and
stratification, interaction with other air masses, mixing episodes, and
dispersion into the regional background. Air parcel trajectories, computed
directly from the balloon wind profiles, show three transport pathways on
18–19 March: (a) high-altitude advection of the top of the MCMA mixed layer,
(b) mid-level outflow over the Sierra Madre Oriental followed by decoupling
and isolated transport over the Gulf of Mexico, and (c) low-level outflow
with entrainment into a cleaner northwesterly jet above the Coastal Plain.
The C-130 aircraft intercepted the balloon-based trajectories three times on
19 March, once along each of these pathways; in all three cases, peaks in
urban tracer concentrations and LIDAR backscatter are consistent with MCMA
pollution. In comparison with the transport models used in the campaign, the
balloon-based trajectories appear to shear the outflow far more uniformly
and decouple it from the surface, thus forming a thin but expansive polluted
layer over the Gulf of Mexico that is well aligned with the aircraft
observations. These results provide critical context for the extensive
aircraft measurements made during the 18–19 March MCMA outflow event and may
have broader implications for modelling and understanding long-range
transport. |
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