In fact, we have seen few places worse than the U.K. Mexico City and Kathmandhu are two; however, in Mexico City they are trying to do something about their problem. One of the most elegant results of remote sensing programs to date shows the Mexico City success. Figure 4 shows as "91" symbols data from 1991 and as "94" data from the same locations in 1994. The emissions reductions are readily apparent. We believe that the major cause is the introduction of closed-loop catalyst systems on the (mostly VW Beetle) taxi cab fleet.

Figure 3. This graph represents carbon monoxide emissions versus model year, with results from three countries: filled squares, Los Angeles, Calif., U.S.A.; open squares, Gothenberg, Sweden; filled triangles, various locations in the U.K.

Despite these research results, there remain critics who believe that our results are random (Pittsburgh Tribune Review, May 15, 1995). This is hard to believe since we routinely show new cars averaging lower emissions than old cars. The video camera and license plate data are independent of the emissions data, thus these results could not be obtained with a random detector.