Continuous VOC Monitoring at the CENICA Supersite during April 2000-2004: A Comparison with the MCMA-2003 Campaign

Since 1999, VOC's have been monitored at CENICA, located in the southeast of the Mexico City Metropolitan Area (MCMA), in order to contribute to the understanding of ozone formation and the presence of toxic air pollutants. CENICA was also the supersite of the MCMA-2003 campaign. This work presents an analysis of the total and thirteen specific VOC's (compounds from C2-C9) measured over some days of the month of April from 2000-2004. Hourly measurements were made throughout the year on four minute samples using a humidifier and cryogenic trap. Samples were analyzed with gas chromatography and FID according to the EPA TO-15 method. The highest and second highest total and specific VOC concentrations were observed during the morning (7-9 am) and night period (9-11 pm), respectively. The highest VOC concentrations were observed for propane, n-butane, acetylene and toluene in both periods. Statistical analysis will be presented to determine if there are significant differences between the different years. Correlations among the 13 VOC's indicated common sources for specific compounds. Therefore, the Chemical Mass Balance Model was applied using samples from 8 am of each year respectively. Preliminary results imply that the GLP contribution increased during this five year period and that the vehicle exhaust contribution decreased in the same time.