Toxic emissions from mobile sources: A total fuel-cycle analysis for conventional and alternative fuel vehicles

Mobile sources are among the largest contributors of four hazardous air pol lutants-benzene, 1,3-butadiene, acetaldehyde, and formaldehyde-in urban are as. At the same time, federal and state governments are promoting the use o f alternative fuel vehicles as a means to curb local air pollution. As yet, the impact of this movement toward alternative fuels with respect to toxic emissions has not been well studied. The purpose of this paper is to compa re toxic emissions from vehicles operating on a variety of fuels, including reformulated gasoline (RFG), natural gas, ethanol, methanol, liquid petrol eum gas (LPG), and electricity. This study uses a version of Argonne Nation al Laboratory's Greenhouse Gas, Regulated Emissions, and Energy Use in Tran sportation (GREET) model, appropriately modified to estimate toxic emission s. The GREET model conducts a total fuel-cycle analysis that calculates emi ssions from both downstream (e.g., operation of the vehicle) and upstream ( e.g., fuel production and distribution) stages of the fuel cycle. We find t hat;almost all of the fuels studied reduce 1,3-butadiene emissions compared with conventional gasoline (CG). However, the use of ethanol in E85 (fuel made with 85% ethanol) or RFG leads to increased acetaldehyde emissions, an d the use of methanol, ethanol, and compressed natural gas (CNG) may result in increased formaldehyde emissions. When the modeling results for the fou r air toxics are considered together with their cancer risk factors, all th e fuels and vehicle technologies show air toxic emission reduction benefits .