ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-6-1733-2006 Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City Marr L. C. 1 2 Dzepina K. 3 Jimenez J. L. 3 Reisen F. 4 Bethel H. L. 4 Arey J. 4 Gaffney J. S. 5 Marley N. A. 5 Molina L. T. 2 Molina M. J. 2 6 Dept. of Civil and Environmental Engineering, Virginia Polytechnic Inst. and State Univ., Blacksburg, Virginia, USA Dept. of Earth, Atmospheric, and Planetary Sciences, Massachusetts Inst. of Technology, Cambridge, Massachusetts, USA Dept. of Chemistry and Biochemistry, and Cooperative Inst. for Research in Environmental Sciences (CIRES), Univ. of Colorado, Boulder, Colorado, USA Air Pollution Research Center and Department of Environmental Sciences, Univ. of California, Riverside, USA Argonne National Laboratory, Illinois, USA now at: Dept. of Chemistry and Biochemistry, Univ. of California, San Diego, USA 23 05 2006 6 6 1733 1745 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/6/1733/2006/acp-6-1733-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/1733/2006/acp-6-1733-2006.pdf

Understanding sources, concentrations, and transformations of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particle-bound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and intercomparison of the methods. The three methods are (1) collection and analysis of bulk samples for time-integrated gas- and particle-phase speciation by gas chromatography/mass spectrometry; (2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and (3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations of particle-phase PAHs typically peak at ~110 ng m<sup>-3</sup> during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentrations during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions.