1NOAA Earth System Research Laboratory, Boulder, Colorado, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
3Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
4Pacific Northwest National Laboratory, Richland, Washington, USA
5University of California, Irvine, California, USA
6Aerodyne Research Inc. Billerca, Massachusetts, USA
7Georgia Institute of Technology, Atlanta, Georgia, USA
8Montana State University, Bozeman, Montana, USA
9Brookhaven National Laboratory, Upton, New York, USA
*now at: NASA Langley Research Center, Hampton, Virginia, USA
**now at: National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, Colorado, USA
Received: 15 Sep 2010 – Discussion started: 08 Oct 2010
Abstract. 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 relative to CO are derived from early-morning measurements. 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. 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. Emission ratios to CO calculated from the results of PMF analysis are compared to emission ratios calculated directly from measurements. The total PIT-MS signal is summed to estimate the fraction of identified versus unidentified VOC species.
Revised: 28 Feb 2011 – Accepted: 08 Mar 2011 – Published: 16 Mar 2011
Bon, D. M., Ulbrich, I. M., de Gouw, J. A., Warneke, C., Kuster, W. C., Alexander, M. L., Baker, A., Beyersdorf, A. J., Blake, D., Fall, R., Jimenez, J. L., Herndon, S. C., Huey, L. G., Knighton, W. B., Ortega, J., Springston, S., and Vargas, O.: 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, Atmos. Chem. Phys., 11, 2399-2421, doi:10.5194/acp-11-2399-2011, 2011.