Greenhouse Gas Emissions from Light Duty Vehicles Under a Variety of Driving Conditions

Data on greenhouse gas (GHG) emissions - carbon dioxide, methane and nitrous oxide (CO₂, CH₄ and N₂O respectively), fuel consumption (U100 km) and fuel economy (miles per US gallon) were collected for 187 light duty gasoline vehicles (cars and light trucks) and 11 light duty diesel cars. Vehicles meeting Tier 1 through Tier 2 emission standards were tested (model years 1997 through 2004). The vehicles were tested over four different driving cycles to simulate different driving conditions, though not all vehicles were tested over all driving cycles. On all of these tests criteria emissions and greenhouse gas emissions (CO₂ and CH₄) were determined. N₂O was determined on 50 of the more recent model year vehicles. The driving cycle used to determine compliance with criteria emissions standards is the Federal Test Procedure (FTP). FTP emission rates vary between 65 and 370 g/km for CO₂, between 0.0007 and 0.11 g/km for CH₄ and between <0.0005 and 0.01 g/km for N₂O. Under highway driving conditions, CH₄ and N₂O emission rates were lower than observed for the FTP. Under congested urban driving conditions, CH₄ and N₂O emissions were significantly greater than observed for the FTP. Under aggressive driving conditions, CH₄ emissions varied while N₂O emissions were always lower than observed for the FTP. The emission factors used in inventory development for CH₄ and N₂O were found to be much greater than the measured emission factors.