On-road remote sensing of vehicle emissions in Mexico

In 1991, the nation of Mexico lowered light-duty vehicle emission standards leading to the introduction of catalytic convertors. On-road emissions were measured in Monterrey, Nuevo Leon, Mexico in 1995 from more than 24 000 vehicles. The Subsecretaria de Ecologia's Office was able to provide vehicle registration information for 10 654 vehicles. These data show a steady emission reduction that coincides with the introduction of light-duty vehicle exhaust emission standards for Mexican vehicles and the implementation of Monterrey's I/M program. The 1995 models are emitting 75% less CO, 70% less HC, and 65% less NO than precontrol models. Pre-1995 models appear to experience a steady degradation in their emission control capabilities, but the cause of this observation cannot reliably be determined without additional data. Comparisons to other locations reveal that Monterrey and Mexico City have improved their fleet emissions when compared to Jugrez despite a shorter time with access to vehicles manufactured with emission control systems. The Monterrey data set can also be used to help explain some of the large on-road reductions observed in Mexico City between 1991 and 1994. Sweden's experience in introducing three-way closed-loop emission control systems suggests that the service life of Mexican vehicle emission control systems can be improved.