HR: 10:20h
AN: A32A-01 INVITED    [Abstracts]
TI: Aerosol Absorption Measurements in MILAGRO.
AU: * Gaffney, J S
EM: jsgaffney@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Marley, N A
EM: namarley@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Arnott, W P
EM: patarnott@physics.unr.edu
AF: University of Nevada, Reno, Mail Stop 220 1664 N. Virgina St., Reno, NV 89957, United States
AU: Paredes-Miranda, L
EM: gparedes@physics.unr.edu
AF: University of Nevada, Reno, Mail Stop 220 1664 N. Virgina St., Reno, NV 89957, United States
AU: Barnard, J C
EM: james.barnard@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352, United States
AB: During the month of March 2006, a number of instruments were used to determine the absorption characteristics of aerosols found in the Mexico City Megacity and nearby Valley of Mexico. These measurements were taken as part of the Department of Energy's Megacity Aerosol Experiment – Mexico City (MAX-Mex) that was carried out in collaboration with the Megacity Interactions: Local and Global Research Observations (MILAGRO) campaign. MILAGRO was a joint effort between the DOE, NSF, NASA, and Mexican agencies aimed at understanding the impacts of a megacity on the urban and regional scale. A super-site was operated at the Instituto Mexicano de Petroleo in Mexico City (designated T-0) and at the Universidad Technologica de Tecamac (designated T-1) that was located about 35 km to the north east of the T-0 site in the State of Mexico. A third site was located at a private rancho in the State of Hidalgo approximately another 35 km to the northeast (designated T-2). Aerosol absorption measurements were taken in real time using a number of instruments at the T-0 and T-1 sites. These included a seven wavelength aethalometer, a multi-angle absorption photometer (MAAP), and a photo-acoustic spectrometer. Aerosol absorption was also derived from spectral radiometers including a multi-filter rotating band spectral radiometer (MFRSR). The results clearly indicate that there is significant aerosol absorption by the aerosols in the Mexico City megacity region. The absorption can lead to single scattering albedo reduction leading to values below 0.5 under some circumstances. The absorption is also found to deviate from that expected for a "well-behaved" soot anticipated from diesel engine emissions, i.e. from a simple 1/lambda wavelength dependence for absorption. Indeed, enhanced absorption is seen in the region of 300-450 nm in many cases, particularly in the afternoon periods indicating that secondary organic aerosols are contributing to the aerosol absorption. This is likely due to carbonyl- and nitro- functional groups on conjugated and aromatic organic structures (e.g. PAH, and terpene derived products). Using 12-hour fine (0.1-1.0 micron) aerosol samples collected in the field on quartz filters, uv/vis and infrared spectra were obtained in the laboratory using integrating spheres and diffuse reflectance spectroscopy, respectively. An inter-comparison of the "real-time" measurements made by the photo-acoustic, aethalometer and MAAP techniques have been described. In addition, the in situ aethalometer (seven-channel) results are compared with continuous integrating sphere uv-visible spectra to examine the angstrom absorption coefficient variance. These results will be briefly overviewed and the specific posters detailing these results will be highlighted highlighted. This work was performed as part of the Department of Energy's Megacity Aerosol Experiment - Mexico City under the support of the Atmospheric Science Program. "This researchwas supported by the Office of Science (BER), U. S. Department of Energy, Grant No. DE-FG02-07ER64329.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0360 Radiation: transmission and scattering
DE: 3359 Radiative processes
DE: 3394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting