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Description de l’éditeur
The main source of atmospheric pollution in all cities is represented by motor vehicles. These consume mostly gasoline and diesel fuel, whose combustion emits into the atmosphere contaminating substances that affect the health of urban populations. The emissions' reduction in order to ameliorate air quality is a priority among urban authorities, and this is prompting the implementation of zero-emissions vehicles. Vehicles fed by fossil fuels contribute with ~25% of the increase in greenhouse gases, which are responsible for global warming. Of the fossil fuels used in vehicles, the least contaminant, both at urban and at worldwide levels, is natural gas. The vehicles utilizing natural gas emit ~20% less carbon dioxide than gasoline vehicles; however, this can revert when considering the possible non-burnt methane losses (Interciencia 18: 285-286, 1993). With the goal of reducing oil dependency, the use of bio-fuels, alone or mixed with gasoline, is being implemented in several countries. In this case, the emissions of "urban contaminants" continue to be significant. As for the emissions of greenhouse gases, these depend upon the origin of the bio-fuel. In general, the evaluation of life cycles ("from the source to the wheel") indicates that the emission reductions are discrete, but when changes in the use of land are involved, the emissions are substantially higher than those produced by fossil fuels (Interciencia 34: 106-112, 2009).