ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-23229-2010 Measurements of volatile organic compounds at a suburban ground site (T1) in Mexico City during the MILAGRO 2006 campaign: measurement comparison, emission ratios, and source attribution Bon D. M. 1 2 3 de Gouw J. A. 1 2 Warneke C. 1 2 Kuster W. C. 1 Alexander M. L. 4 Baker A. 5 Beyersdorf A. 5 10 Blake D. 5 Fall R. 2 3 Jimenez J. L. 2 3 Herndon S. C. 6 Huey L. G. 7 Knighton W. B. 8 Ortega J. 4 Springston S. 9 Ulbrich I. M. 2 3 Vargas O. 7 NOAA Earth System Research Laboratory, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA Pacific Northwest National Laboratory, Richland, Washington, USA University of California, Irvine, California, USA Aerodyne Research Inc. Billerca, Massachusetts, USA Georgia Institute of Technology, Atlanta, Georgia, USA Montana State University, Bozeman, Montana, USA Brookhaven National Laboratory, Upton, New York, USA now at: NASA Langley Research Center, Hampton, Virginia, USA 08 10 2010 10 10 23229 23286 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-discuss.net/10/23229/2010/acpd-10-23229-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/23229/2010/acpd-10-23229-2010.pdf

Volatile organic compound (VOC) mixing ratios were measured with two different instruments at the T1 ground site in Mexico City during the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign in March of 2006. A gas chromatograph with flame ionization detector (GC-FID) quantified 18 light alkanes, alkenes and acetylene while a proton-transfer-reaction ion-trap mass spectrometer (PIT-MS) quantified 12 VOC species including oxygenated VOCs (OVOCs) and aromatics. A GC separation system was used in conjunction with the PIT-MS (GC-PIT-MS) to evaluate PIT-MS measurements and to aid in the identification of unknown VOCs. The VOC measurements are also compared to simultaneous canister samples and to two independent proton-transfer-reaction mass spectrometers (PTR-MS) deployed on a mobile and an airborne platform during MILAGRO. VOC diurnal cycles demonstrate the large influence of vehicle traffic and liquid propane gas (LPG) emissions during the night and photochemical processing during the afternoon. Emission ratios for VOCs and OVOCs are determined from early-morning enhancement ratios and compared to emission ratios calculated from the PMF results. Average emission ratios for non-oxygenated species relative to CO are on average a factor of 2 higher than measured for US cities. Emission ratios for OVOCs are estimated and compared to literature values the northeastern US and to tunnel studies in California. Positive matrix factorization analysis (PMF) is used to provide insight into VOC sources and processing and to estimate OVOC emission ratios. Three PMF factors were distinguished by the analysis including the emissions from vehicles, the use of liquid propane gas and the production of secondary VOCs + long-lived species. The total PIT-MS signal was summed to estimate the fraction of identified vs. unidentified VOC species.

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