Emissions of nitrous oxide and methane from conventional and alternative fuel motor vehicles

This paper provides estimates of emissions of two important but often not well-characterized greenhouse gas (GHG) emissions related to transportation energy use: methane (CH4) and nitrous oxide (N2O). The paper focuses on emissions of CH4 and N2O from motor vehicles because unlike emissions of CO2, which are relatively easy to estimate, emissions of CH4 and N2O are a function of many complex aspects of combustion dynamics and of the type of emission control systems used. They therefore cannot be derived easily and instead must be determined through the use of published emission factors for each combination of fuel, end-use technology, combustion conditions, and emission control system. Furthermore, emissions of CH4 and N2O may be particularly important with regard to the relative CO2-equivalent GHG emissions of the use of alternative transportation fuels, in comparison with the use of conventional fuels. By analyzing a database of emission estimates, we develop emission factors for N2O and CH4 from conventional vehicles, in order to supplement recent EPA and IPCC estimates, and we estimate relative emissions of N2O and CH4 from different alternative fuel passenger cars, light-duty trucks, and heavy-duty vehicles.