Fig. 3 presents the distribution of emissions according to fuel use and major vehicle type.
The four main groups contributed about equally to CO emissions. Although heavy-duty vehicles were small in number compared to the total fleet (2%), their emissions represented 23% of total CO2 emissions, nearly equaling those of gasoline and diesel vehicles, because of their high number of VKT and the associated high fuel consumption values. Gasoline light-duty vehicles were the main emitters of CO and NMVOC, accounting for 85% and 65% of emissions respectively, while they only represented a small fraction (-20%) of CH4 , N2O, NO and SO emissions. Together, diesel light and heavy-duty vehicles were responsible for almost all PM emissions, 80% of SO emissions and 55% of NOx emissions, while they accounted for only 4% of CO emissions.
CNG light-duty vehicles were the main emitters of CH4 and N2O, accounting for more than 70% in both cases.