Introduction Spain is currently the top producer of concentrated

Table 5 shows data for the emissions of the regulated pollutants from non-hybrid diesel and CNG buses for each of the five different driving cycles; this AG 1879 data includes all exhaust after-treatment technologies. It is clear that the NYBus and Paris cycles generally had the highest emissions for a specific pollutant and fuel, while the OCC and Braun cycles had the lowest emissions. For all five driving cycles, the HC emissions for the CNG fueled buses were higher than for diesel fueled vehicles. NOx emissions were not significantly different for diesel and CNG fueled buses for all of the test cycles, with the exception of the Paris cycle, while the CNG fueled emissions of NOx were significantly lower. CO emissions were not significantly different for diesel and CNG fueled buses for all of the test cycles, with the exception of the CBD cycle, where the CNG fueled emissions of CO were significantly greater. PM emissions with CNG fuels were significantly lower than growth hormone (GH) for diesel fuels for each of the test cycles.