Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
2-22
servicing these units, or during their retirement; at which time the HFCs can be
recycled. Efforts to prevent these leaks, such as strengthening the requirement
and training of technicians to use recovery equipment, and not vent refrigerant
during equipment service, have reduced emissions. Investigating new
refrigerants with lower GWP values could decrease the global warming effect of
future releases of current refrigerants.
Figure 2.13 shows the steady increase in HFC emissions from 1990 to 2006
associated with the gradual introduction of HFCs to replace CFCs and HCFCs as
common refrigerants. HFC emissions plateau after 2005, possibly due to better
leak prevention and completion of the HFC phase-in.
Figure 2.13 HFC Emissions from Mobile Air Conditioners and Refrigerated
Transport
MMT CO2e
80
70
60
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Source: U.S. EPA (2008). Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 to 2006.
2.3 LIFE-CYCLE TRANSPORTATION GREENHOUSE GAS
EMISSIONS
A primary source of transportation greenhouse gases is the combustion of fuel or
other energy sources to power vehicles, also known as “tailpipe” emissions.
However, transportation depends on an array of other processes that also
produce additional GHG emissions. These include the production and
distribution of fuel, the manufacture of vehicles, and the construction and
maintenance of transportation infrastructure. These supporting processes—
known as the fuel, vehicle manufacture, and infrastructure cycles—generally are
not included in U.S. transportation sector GHG estimates. Many of these
processes are included in U.S. industrial sector estimates, and some occur
overseas, and are therefore excluded from estimates of U.S. transportation sector
GHG emissions. However, these processes are important elements of the