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

Journal Article · Wed Aug 04 04:00:00 EDT 2010 · Atmospheric Chemistry and Physics, 10(15):7137–7159

DOI:https://doi.org/10.5194/acp-10-7137-2010· OSTI ID:991584

Voss, Paul B; Zaveri, Rahul A; Flocke, Frank M; Mao, Huitimg; Hartley, Tom; DeAmicis, Pam; Deonandan, Indira; Contrerars-Jimenez, G; Martinez-Antonio, O; Figueroa Estrada, M; Greenberg, David; Campos, Teresa; Weinheimer, Andrew J; Knapp, David; Montzka, DeeDee; Crounse, J D; Wennberg, P O; Apel, Eric; Madronich, Sasha; de Foy, B

One of the major objectives of the Megacities Initiative: Local And Global Research 3 Observations (MILAGRO 2006) campaign was to investigate the long-range transport of 4 Mexico City Metropolitan Area (MCMA) pollution outflow and its downwind impacts on air 5 quality and climate. Four aircraft (DOE G-1, NSF/NCAR C-130, NASA-J31, and NASA 6 DC-8) made extensive chemical, aerosol, and radiation measurements above MCMA and over 7 1000 km downwind in order to characterize the evolution of MCMA pollution as it aged and 8 dispersed over the central Mexican plateau and the Gulf of Mexico. As part of this effort, 9 free-floating Controlled-Meteorological (CMET) balloons, capable of changing altitude on 10 command via satellite, characterized the MCMA outflow by performing repeated soundings 11 during the transit. In this paper, we present an analysis based on the data from two CMET 12 balloons that were launched near Mexico City on the afternoon of 18 March 2006 and floated 13 downwind with the outflow for nearly 30 hours. Continuous profile measurements made by 14 the balloons show the evolving structure of the MCMA outflow in considerable detail: its 15 stability and stratification, interaction with other air masses, mixing episodes, and dispersion 16 into the regional background. Air parcel trajectories, computed directly from the balloon 17 wind profiles, show three different transport pathways for Mexico City outflow on 18-19 18 March: (a) high-altitude advection of the top of the MCMA mixed layer, (b) low-altitude flow 19 over the Sierra Madre Oriental followed by decoupling and isolated transport over the Gulf, 20 and (c) the same decoupling scenario with entrainment into a cleaner westerly jet below the 21 plateau. The C-130 intercepted the balloon-based trajectories three times on 19 March, once 22 along each transport pathway. In all three cases, distinct peaks in the urban tracer signature 23 and LIDAR backscatter imagery provided evidence for Mexico City air. The coherence of the 24 high-altitude outflow was well preserved after 25 hours whereas that lower in the atmosphere 25 was more widely dispersed over the same time period. Other C-130 intercepts, previously 26 thought to be from Mexico City, are shown to have likely originated elsewhere. These 27 findings address key questions about the long-range transport of Mexico City pollution and its 28 impact on the regional background. The particular intercepts identified should prove useful in 29 answering a wide range scientific questions pertaining to the transport, transformation, and 30 downwind impacts of megacity air pollution. 31 32

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 991584
• Report Number(s): PNNL-SA-70484; KP1701000
• Journal Information: Atmospheric Chemistry and Physics, 10(15):7137–7159, Journal Name: Atmospheric Chemistry and Physics, 10(15):7137–7159 Journal Issue: 15 Vol. 10
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADVECTION
AIR POLLUTION
AIR QUALITY
AIRCRAFT
ALTITUDE
DECOUPLING
ENTRAINMENT
GULF OF MEXICO
LONG-RANGE TRANSPORT
NASA
OPTICAL RADAR
POLLUTION
RADIATIONS
STABILITY
STRATIFICATION
TRAJECTORIES
TRANSPORT
URBAN AREAS