Environ. Sci. Technol. 2003, 37, 196-200
Evaluation of the Vehicle Inspection/ Maintenance Program in the Metropolitan Area of Mexico City I . S C H I F T E R , * L . D IÄ A Z , M . V E R A , E . G U Z M AÄ N , J . D U R AÄ N , F . R A M O S , A N D E. LO Ä PEZ-SALINAS Instituto Mexicano del Petro´leo, Competencia de Estudios Ambientales, Eje Central 152, Me´xico, D.F., 07730 Mexico
The Inspection/Maintenance Program in the Metropolitan Area of Mexico City (MAMC) mandates a test every 6 months for all gasoline motor vehicles as one of the strategies to decrease emissions of vehicular pollutants. FTP-75 and ASM procedures were performed in our facilities to a fleet of 108 in-use motor vehicles before and after the approval of the I/M mandatory test. When our laboratorysimulated ASM data were compared with those of the official certificate, a large difference was observed between them. On the other hand, audits at the test-only centers indicate poor maintenance of the analytical instruments and dynamometers. On the basis of our FTP results, an estimation of the emissions change for the MAMC fleet shows a net 4% decrease in CO emissions, while total hydrocarbons and NOx increased 9 and 8%, respectively. Our results indicate that the I/M system in the MAMC lacks the technical capability and investment to ensure that software and hardware are properly maintained, calibrated, and upgraded. Sometimes limited attention is paid to ensure adequate training of inspectors, auditors, and quality control staff.
Introduction In the metropolitan area of Mexico City (MAMC), three types of emission control programs for vehicles have been implemented. The first program set emission standards on newly manufactured vehicles. The second one focused on improving the fuel composition, and the third one, which started in 1988, is the mandatory Inspection & Maintenance (I/M) Program twice a year to all vehicles (1, 2). Considering that the average lifetime of vehicles in the developed world is much longer than in Europe or the United States, the purpose of I/M is to identify poorly maintained or defective vehicles and to ensure that they are properly repaired. Many countries in Asia, for instance, have adopted emission standards for new vehicles, but there is still limited capacity for testing and verifying compliance with the requirements. A properly operating I/M program can be an important element of a comprehensive air quality management plan by significantly reducing emissions from the entire fleet of inspected vehicles (3). I/M programs are often characterized as “centralized” or “decentralized”. Test-and-repair networks generally consist of large number of low-volume repair garages owned and operated by a separate entity or person. Test-only networks generally involve a single entity or contractor that conducts * Corresponding author e-mail:
[email protected]; phone: (+52)55-3003-8507; fax: (+52)55-3003-8484. 196
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only the testing, while repairs are done at an independent garage. In the case of the MAMC, the I/M program is based on the acceleration simulation mode (ASM) test system (4). A recent report of the National Research Council states that I/M programs have generally achieved less emissions reduction than originally projected (5). Independent and statesponsored evaluations of ongoing I/M programs have estimated that the emissions reductions attributable to these programs are from zero to about one-half of the reductions predicted by the models. There is considerable interest, therefore, from the state authorities and local transportation officials in knowing the degree to which implemented emissions control strategies in mobile sources are actually accomplishing their intended objective (6). Experience from many countries indicates that test-only, single-contractor-operated I/M systems have produced the best results. Test-and-repair systems have been much less successful because they are very difficult to supervise and audit and have been found to be subject to corruption. Notwithstanding, several countries are adopting hybrid systems that combine elements of both approaches, which raises concerns about their overall effectiveness. In the present conditions of the Mexican I/M program, all vehicles must pass the test twice a year at test-only stations. If they fail, they are not allowed to circulate. Owners of vehicles must repair their vehicles at their own expense. Thus, no official repair garages exist where the authorities gather information on the failure rates. Therefore, the I/M program, being the most important mechanism to control emissions, must be performed with the highest standards to pinpoint high-emitting vehicles. In this work, a stratified sample of 108 in-use vehicles was selected and evaluated with mass emission (e.g., Federal Test Procedure, FTP-75) and concentration tests (e.g., ASM), under controlled conditions in our laboratories, before and after the vehicles passed or failed the official I/M protocol. After the vehicles obtained the certificate result, we audited the I/M stations where the tests were performed, to evaluate the accuracy of their emissions equipment and procedures. From the data obtained from our FTP tests, any expected change in emissions of the entire vehicle fleet in the MAMC in order to assess I/M effectiveness to reduce emissions was estimated.
Experimental Section Chassis Dynamometer Emission Measurements. All measurements were obtained from July to September 2000. The required sample of vehicles was reduced by stratified sampling. In this technique, the fleet is divided into several groups. Typically, different ranges of model years (MYs) are used, which act as a surrogate for different emission control technologies. Vehicles covered a range of MYs representative of the MAMC, according to the fleet distribution reported by the World Bank (7). One hundred eight units were recruited in areas of the MAMC of different socioeconomic indicators through newspaper ads, used car dealers, and repair garages in exchange of payment of the mandated I/M certificate fees. The number of vehicles recruited aimed to include a high number of hypothetically high emitters. However, one has to be aware that recruited vehicles have serious bias issues because high emitters, tampered vehicles, and expensive luxurious vehicles are less likely to be voluntarily submitted for testing. Emissions from high-emitting vehicles are much more variable than emissions from normal emitters (8). Thus, it requires a large sampling fraction to obtain reasonably accurate estimates for the emissions control programs. 10.1021/es020549t CCC: $25.00
2003 American Chemical Society Published on Web 12/04/2002
TABLE 1. Distribution of Vehicles in the MAMC, Percentage and Number of Units Tested in This Work type of vehicle private
taxis
vehicle technology
MY
no. of units in MAMC
% distribution
units tested (% distribution)
fuel injection, close loop, TWCa fuel injection, TWC carburated, oxidative catalyst carburated, no emission control carburated, no emission control fuel injection, close loop, TWC carburated, oxidative catalyst carburated, no emission control
1995-2000 1993-1994 1991-1992 1986-1990
