HR: 1340h
AN: A43C-1419    [Abstracts]
TI: Enhanced UV Absorption in Carbonaceous Aerosols during MILAGRO and Identification of Potential Organic Contributors.
AU: * Mangu, A
EM: axmangu@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Kelley, K L
EM: kxbrock@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Marchany-Rivera, A
EM: angierosy@gmail.com
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Kilaparty, S
EM: kspramila@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
AU: Gunawan, G
EM: gxgunawan@ualr.edu
AF: University of Arkansas at Little Rock, 2801 S. University Avenue, Little Rock, AR 72204, United States
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
AB: Measurements of aerosol absorption were obtained as part of the MAX-Mex component of the MILAGRO field campaign at site T0 (Instituto Mexicano de Petroleo in Mexico City) during the month of March, 2006 by using a 7- channel aethalometer (Thermo-Anderson). These measurements, obtained at 370, 470, 520, 590, 660, 880, and 950 nm at a 5 minute time resolution, showed an enhanced absorption in the UV over that expected from carbon soot alone. Samples of fine atmospheric aerosols (less than 0.1micron) were also collected at site T0 and T1 (Universidad Technologica de Tecamac, State of Mexico) from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. The samples were collected on quartz fiber filters with high volume impactor samplers. The samples have been characterized for total carbon content (stable isotope ratio mass spectroscopy) and natural radionuclide tracers (210Pb, 210Po, 210Bi, 7Be, 13C, 14C, 40K, 15N). Continuous absorption spectra of these aerosol samples have been obtained in the laboratory from 280 to 900nm with the use of an integrating sphere coupled to a UV-visible spectrometer (Beckman DU with a Labsphere accessory). The integrating sphere allows the detector to collect and spatially integrate the total radiant flux reflected from the sample and therefore allows for the measurement of absorption on highly reflective or diffusely scattering samples (1). The continuous spectra also show an enhanced UV absorption over that expected from carbon soot and the general profiles are quite similar to those observed for humic and fulvic acids found as colloidal materials in surface and groundwaters (2), indicating the presence of humic-like substances (HULIS) in the fine aerosols. The spectra also show evidence of narrow band absorbers below 400 nm typical of polycyclic aromatics (PAH) and nitrated aromatic compounds. Spectra were also obtained on NIST standard diesel soot (SRM 2975), NIST standard air particulate matter (SRM 8785), and nitrated PAH compounds for comparison. Potential organic aerosol components are identified which contribute to the enhanced absorption observed in the field. The wavelength dependence of the mass specific absorption is obtained from these spectra and total carbon measurements. The wavelength dependence of the aerosol complex refractive index (m = n +ik) in the UV-visible spectral region is determined by application of the Kramers Kronig function. The importance of the aerosol absorption in the infrared spectral region to radiative forcing will be discussed. 1. Marley, N.A., J.S. Gaffney, J.C. Baird, C.A. Blazer, P.J. Drayton, and J.E. Frederick, Aerosol Sci. Technol., 34, 535-549, (2001). 2. N.A. Marley, J.S. Gaffney, and K.A. Orlandini, Chapter 7 in Humic/Fulvic Acids and Organic Colloidal Materials in the Environment, ACS Symposium Series 651, American Chemical Society, Washington, D.C., pp. 96-107, 1996. This work was conducted as part of the Department of Energy's Atmospheric Science Program as part of the Megacity Aerosol Experiment – Mexico City during MILAGRO. This research was supported by the Office of Science (BER), U.S. Department of Energy Grant No. DE-FG02-07ER64329. We also wish to thank Mexican Scientists and students for their assistance from the Instituto Mexicano de Petroleo (IMP) and CENICA.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0360 Radiation: transmission and scattering
DE: 0394 Instruments and techniques
DE: 3394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting