Characterization of on-road vehicle emissions in the Mexico City Metropolitan Area using a mobile laboratory in chase and fleet average measurement modes during the MCMA-2003 field campaign

摘要

A mobile laboratory was used to measure on-road vehicle emission ratiosduring the MCMA-2003 field campaign held during the spring of 2003 in theMexico City Metropolitan Area (MCMA). The measured emission ratios representa sample of emissions of in-use vehicles under real world drivingconditions for the MCMA. From the relative amounts of NO_x and selectedVOC's sampled, the results indicate that the technique is capable ofdifferentiating among vehicle categories and fuel type in real world drivingconditions. Emission ratios for NO_x, NO_y, NH₃, H₂CO,CH₃CHO, and other selected volatile organic compounds (VOCs) arepresented for chase sampled vehicles in the form of frequency distributionsas well as estimates for the fleet averaged emissions. Our measurements ofemission ratios for both CNG and gasoline powered "colectivos" (publictransportation buses that are intensively used in the MCMA) indicate that – in a mole per mole basis – have significantly larger NO_x and aldehydesemissions ratios as compared to other sampled vehicles in the MCMA.Similarly, ratios of selected VOCs and NO_y showed a strong dependenceon traffic mode. These results are compared with the vehicle emissionsinventory for the MCMA, other vehicle emissions measurements in the MCMA,and measurements of on-road emissions in U.S. cities. We estimate NO_xemissions as 100 600±29 200 metric tons per year for light dutygasoline vehicles in the MCMA for 2003. According to these results, annualNO_x emissions estimated in the emissions inventory for this categoryare within the range of our estimated NO_x annual emissions. Ourestimates for motor vehicle emissions of benzene, toluene, formaldehyde, andacetaldehyde in the MCMA indicate these species are present inconcentrations higher than previously reported. The high motor vehiclealdehyde emissions may have an impact on the photochemistry of urban areas.