Potential impacts of compressed natural gas in the vehicular fleet of Mexico City

One of the control measures to decrease urban air pollution in Mexico City is the introduction of compressed natural gas in gasoline-powered vehicles. In this study, an in-use vehicular fleet, representative of Mexico City's total vehicle population, was selected and converted to use natural gas. A comparison of emission factors for total hydrocarbons, CO, and NOx were obt ained from the gasoline-and gas-powered vehicles using the Federal Test Pro cedure (FTP-75). Average emissions reductions from private cars and taxis, the most numerous fleet type, were 88% for CO, 91% for non-methane hydrocar bons, and 40% NOx. However, there is a 13% emissions increase in total hydr ocarbons (that is, including methane). Speciated hydrocarbon data were used to estimate the potential of the emissions to form ozone and to predict th e impact of fuel changes on air quality. In average, emissions from natural gas-converted vehicles were 2.3 times less reactive to form ozone than tho se from same vehicle fleet when gasoline-powered. Considering present natur al gas-powered vehicles growth rate, regulated emissions reductions until t he year 2007 were estimated.