The contribution of gasoline-powered vehicles to air toxic emissions in the Metropolitan Area of Mexico City (MAMC) is not well established. The MAMC has particular geographic conditions such as being in a valley at high altitude (2280 m above sea level) and has a very old and technologically heterogeneous vehicular fleet. Toxic compounds emitted by the exhaust of motor vehicles (e.g., benzene, 1,3-butadiene, formaldehyde, and acetaldehyde) were estimated. In this work, tests using Mexican gasolines in a vehicular fleet representative of the MAMC (ca. 1999) were carried out. As a comparison, some tests were done using an American gasoline (Federal Reformulated Gasoline, RFG-1) in a representative fleet of vehicles operated in Mexico

The metropolitan area of Mexico City is the urban area of the country that presents the most critical environmental problem due to fuel consumption. Attempting to reduce the ambient concentration of pollutants, the environmental program adopted consisted of a broad series of strategies designed to improve the air quality. Modification of fuel formulation, which include composition and physical properties, provide a particularly effective way to reduce emissions. The reformulated gasoline in Mexico has reduced aromatics, olefins, and benzene contents as well as a lower Reid vapor pressure. The regulated emissions (carbon monoxide, total hydrocarbons, and nitrogen oxides) were evaluated for each vehicle as well as the speciated hydrocarbons present in the exhaust emission. With these data, we estimated the ozone-forming potential of the fuels and correlate the results with the technology of the vehicles. When these data are compared with those obtained in United States, there is an important difference in the technological devices related to emission control in vehicles of the Mexican market. Moreover, our results strongly suggest that emission standards for new vehicles sold in Mexico must be tighten further in order equal those demanded in other countries.

The environmental agency in the metropolitan area of Mexico City has launched a program to introduce more energy-efficient modes of transport, one of which is the use of alternative and less polluting fuels. With the perspective in mind, a liquefied petroleum gas (LPG) fleet of vehicles is exempt of the mandatory "one day without a car" program if the emission of pollutants is below the standard authorized for that specific purpose. Today, about 28,000 light-duty vehicles and heavy-duty trucks circulate in the area, most of them as aftermarket converted vehicles. In this work, we evaluated regulated exhaust emission and other parameters on 134 representative vehicles of that fleet. From the data obtained, an estimate of emission factors and their contribution to the global emission in the metropolitan area is provided. It is concluded that more than 95% of the in-use vehicles using LPG presented regulated emissions which exceeded in one or more the environmental regulations values required for certification. The poor maintenance of the vehicles and the type of conversion kit installed could be the culprits of the results obtained.

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A 1999 ordinance by the Government of Mexico City bans 1993 model-year vehicles from on-road operation if their catalytic converters are not replaced with new ones. To validate the benefits of this action, we examined three issues related to exhaust emissions of vehicles equipped with catalytic converters. After selecting representative fleets of in-use vehicles, a comparison between emissions and catalyst efficiency in cars with two categories of exhaust emission limits was carried out. For that purpose, two fleets were selected, each made up of 10 vehicles run under similar conditions. A third, larger fleet with emissions control systems was used to evaluate and simulate real-world conditions of vehicles in a controlled laboratory. Finally, the aging effect on the catalytic converter was studied on vehicles run for 100,000 km, replacing their old emission control devices for new ones.The 1991 FTP-75. Our results suggest that the replacement of old catalytic converters with new ones will have little effect on decreasing polluting emissions because these vehicles were in very bad mechanical condition. Results of catalytic activity as a function of mileage indicated inefficient catalyst performance for the fleets tested. All pollutant conversions were below 90% efficiency, and they deteriorated by an average of 30% after the vehicles were run for 100,000 km.