Evaluation of Volatile Organic Compounds in Mexico City Metropolitan Area 2005- 2006

One of the main air quality problems in the Mexico City Metropolitan Area (MCMA) are the high ozone levels, resulting from the photochemical reactions among precursors such as nitrogen oxides and volatile organic compounds. The MCMA air quality monitoring network includes 19 NOx and 19 O3 monitoring sites. However, no routine VOC monitoring is carried out. This work presents results of a field campaign done from September 2005 to September 2006 in the MCMA. 24 hours integrated samples were obtained every six days in five different sites, considered representative of the northwest, northeast, southeast, southwest, and center of the MCMA. Samples were obtained in stainless steel canisters adapted with a programmable flow controller. Analyses were done using a GC-FID to identify 57 VOCs following USEPA-TO-14A. A total of 354 samples were obtained corresponding to 62 sampling days. On the average, highest concentrations were found in the center, whereas lowest concentrations were found at the southwest. However, the overall maximum concentration (741 ppbV) was determined at the northeast site, and the overall minimum concentration (27 ppbV) was determined at the southwest site. At all sites, propane, butane, acetylene and toluene were the compounds found at highest concentrations. The main source for propane and butane is LPG, whereas for acetylene and toluene are combustion and evaporation of gasoline. It was found that southwest site is significantively different from the rest of all sites. A short field campaign was also done during 5 days in November-December 2005 with 3 periods of 3hrs integrated samples.