GAW Report No. 205 - IGAC Project

CHAPTER 5 – NORTH AMERICAEmission inventories have been developed in the MCMA since 1986. There were largeuncertainties in the early inventories, especially for VOC emissions [Molina and Molina, 2002].Figure 15 presents the 2006 MCMA emissions inventory for PM 10 , PM 2.5 , VOC and NO X [SMA-GDF, 2008]. Mobile emission sources represent a significant fraction of the total anthropogenicemissions of NO X and PM 2.5 (76% and 62%, respectively) but only a relatively small fraction (34%)of VOC. However, ambient VOC measurements suggest that emissions associated with gasolineemissions dominate in MCMA as well as some other mega-cities [Parrish et al., 2009a]. As in allcurrent emission inventories throughout the world, a great deal more effort is required for emissioninventory testing and improvement.Figure 15 - Emissions inventory for the Year 2006 [SMA-GDF, 2008]The combination of population, topography, meteorology, and multi-pollutant emissiondensity of the MCMA has attracted a number of field studies. The Mexico City Air QualityResearch Initiative (MARI) project gathered surface and vertical profile observations ofmeteorology and pollutants during 1990-1994 [Streit and Guzman, 1996]. The IMADA-AVER(Investigación sobre Materia Particulada y Deterioro Atmosférico, Aerosol and Visibility EvaluationResearch) campaign in February - March 1997 yielded comprehensive meteorologicalmeasurements in the basin, and provided insights into particulate composition [Doran et al., 1998;Edgerton et al., 1999]. The MCMA-2002/2003 campaigns in February 2002 and April 2003provided detailed measurements of many oxidant precursors and photochemical intermediatesincluding radicals, as well as meteorology and emissions [Molina et al., 2007]. The largest study todate, MILAGRO (Megacity Initiative: Local and Global Research Observations), took place inMarch 2006 and included a wide range of instruments at ground sites, on aircraft, and satellitesthat provided detailed measurements of gas and aerosol chemistry, aerosol microphysics andoptics, radiation and meteorology [Molina et al., 2010; Singh et al., 2009; and references therein].The intensive field campaigns have provided a wealth of information on the emission,dispersion and transformation of species emitted to the MCMA atmosphere and their urban,regional and hemispheric impacts. Motor vehicles produce abundant amounts of VOC and NO X(ozone and aerosol precursors), primary PM, elemental carbon, particle-bound polycyclic aromatichydrocarbons, CO and a wide range of air toxics, including formaldehyde, acetaldehyde, benzene,183