Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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PIT-MS Measurements of VOCs at a suburban ground site (T1) in Mexico City during the MILAGRO 2006 campaign: Emission Ratios and Source Apportionment

Daniel Welsh-Bon, Carsten Warneke, William Kuster, Joost de Gouw, Oscar Vargas, Greg Huey, Jose L. Jimenez and Ingrid M. Ulbrich

Volatile organic compounds (VOCs) were measured by several different methods at a suburban ground site (T1) in Mexico City located approximately 30 km north east of the city center during the MILAGRO campaign in March, 2006. For most primary emissions a strong diurnal variation was observed with very high mixing ratios at night when VOC emissions accumulated in a shallow boundary layer, and lower mixing ratios during the day when VOCs were mixed in a deeper boundary layer and were removed by photochemistry. Diurnal patterns in VOC measurements were substantially different for oxygenated VOCs. Emission ratios for primary VOCs in Mexico City are generally a factor of 2 higher than typical values observed for cities in the United States. Positive Matrix Factorization (PMF) analysis clearly distinguishes compounds with only primary emissions (e.g. alkanes, alkenes, and aromatics) from oxygenated species (e.g. acetaldehyde, acetone), which have both direct emission sources and a large proportion of secondary formation. PMF analysis results are shown to depend on the individual atmospheric lifetimes of VOCs included in the analysis. A novel application of PMF provides chemical information about unknown VOCs and is used to estimate VOC emission ratios.