HR: 14:40h
AN: A23D-05    [Abstracts]
TI: Concentrations, Sources, and Transformation of Particulate Polycyclic Aromatic Hydrocarbons in Mexico City
AU: * Marr, L C
EM: lmarr@vt.edu
AF: Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, 411 Durham Hall, Blacksburg, VA 24061 United States
AU: * Marr, L C
EM: lmarr@vt.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Dzepina, K
EM: katja.dzepina@colorado.edu
AF: Department of Chemistry and Biochemistry, Cooperative Institute for Research in the Environmental Sciences, University of Colorado, UCB 216, Boulder, CO 80309 United States
AU: Jimenez, J L
EM: jose.jimenez@colorado.edu
AF: Department of Chemistry and Biochemistry, Cooperative Institute for Research in the Environmental Sciences, University of Colorado, UCB 216, Boulder, CO 80309 United States
AU: Bethel, H L
AF: Air Pollution Research Center, University of California, 900 University Avenue, Riverside, CA 92521 United States
AU: Riesen, F
AF: Air Pollution Research Center, University of California, 900 University Avenue, Riverside, CA 92521 United States
AU: Arey, J
EM: janet.arey@ucr.edu
AF: Air Pollution Research Center, University of California, 900 University Avenue, Riverside, CA 92521 United States
AU: Gaffney, J S
EM: gaffney@anl.gov
AF: Environmental Research Division, Argonne National Laboratory, Building 203/ER, Argonne, IL 60439 United States
AU: Marley, N A
EM: marley@anl.gov
AF: Environmental Research Division, Argonne National Laboratory, Building 203/ER, Argonne, IL 60439 United States
AU: Brune, W H
EM: whb2@psu.edu
AF: Department of Meteorology, Pennsylvania State University, 503 Walker Building, University Park, PA 16802 United States
AU: Shirley, T R
EM: trs161@psu.edu
AF: Department of Meteorology, Pennsylvania State University, 503 Walker Building, University Park, PA 16802 United States
AU: Molina, L T
EM: ltmolina@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Molina, M J
EM: mmolina@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: Understanding ambient concentrations of polycyclic aromatic hydrocarbons (PAHs) and their transformation in the atmosphere is important because of their potent mutagenicity and carcinogenicity and potential role as indicators for aerosol aging. The measurement of particulate polycyclic aromatic hydrocarbons by three different methods during the Mexico City Metropolitan Area air quality study in 2003 (MCMA-2003) presents a unique opportunity for characterization of these compounds. The three methods are (1) time-integrated filter samples for detailed speciation of PAHs; (2) aerosol photoemission for quantification of surface-bound PAHs at high time resolution; and (3) aerosol mass spectrometry for measurement of total and size-resolved PAHs. While the results from the three techniques generally agree, certain disparities emphasize methodological limitations or interesting PAH behavior. Total particle-bound PAH concentrations measured by photoemission and by traditional filter methods are correlated, except during the morning, when filter reaction artifacts may lead to underestimation of actual concentrations. Speciation profiles and diurnal patterns suggest that motor vehicles are the predominant daytime source of PAH emissions in the MCMA. The presence of triphenylbenzene and retene indicate that garbage and wood burning are also important sources of PAHs. For the first time, ambient PAHs were detected by an aerosol mass spectrometer (AMS). The AMS is able to quantify bulk phase PAHs that aerosol photoemission, a surface technique, cannot. Ambient particle-bound PAH concentrations exhibit a strong diurnal pattern. They typically peak at ~100 ng m$^{-3}$ during the morning rush hour and then rapidly decrease to a steady daytime level of ~10 ng m$^{-3}$, with the photoemission signal dropping much faster than black carbon concentrations. We explore two hypotheses to explain this behavior: coating of soot particles by secondary aerosol compounds causing the suppression of the photoemission signal, and reaction of particle-bound PAHs with OH. The first explanation is important because coating of soot particles greatly affects their light absorption properties, with implications for climate and visibility. The second explanation could have important implications for PAH-related health effects, due to the formation through heterogeneous reactions of compounds that are either more or less toxic than the original PAHs. Additionally, condensation and/or heterogeneous reactions may transform soot particles into more effective condensation nuclei.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting