The main components of automobile exhaust are carbon dioxide (CO2) and water vapor (H2O). Carbon dioxide is the most important anthropogenic greenhouse gas (GHG) and the most significant Greenhouse Gas emitted in the U.S. (with 82-84% of all U.S. emissions).[1] Increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change.[2]
The CO2 emission standards can be referred to the fuel or to the vehicle :
CO2 mass emission in vehicles is measured in g/km (g/mi * 0.621371192 = g/km).
Transportation accounts for forty percent of California's annual greenhouse gas emissions, and California relies on petroleum-based fuels for 96 percent of its transportation needs.
The Californian Governor Arnold Schwarzenegger issued an Executive Order in January 2007 for California adopt a Low-Carbon Fuel Standard (LCFS).[3] The LCFS requires oil refineries to ensure that the mix of fuel they sell in the California Market meets, on average, a declining target for greenhouse gas emissions measured in CO2-equivalent grams per unit of fuel energy sold. By 2020, the LCFS will produce a 10 % reduction in carbon intensity from production and use of transport fuels in California.[4]