Propane's Environmental Impact |
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| Reducing Emissions, One Gallon at a Time |
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Propane is not a direct greenhouse
gas when released into the air. Current measurements have not found a global
climate impact from propane emissions (Intergovernmental Panel on Climate
Change-IPCC). Compared to conventional fuel sources, propane generates fewer GHG
emissions in almost every application. At the point of use, propane has a lower
carbon content than gasoline, diesel, heavy fuel oil, or even biodiesel and
ethanol.
Propane represents a small but important part of the U.S. energy. Because of
propane’s relatively low GHG emission rate, its share of GHG emissions is smaller
than its share of energy supply.
When quantifying the greenhouse gas emissions that result from the use of energy,
it is important to distinguish between the emissions released at the location
where the energy is consumed and the emissions released as a result of extracting,
processing and delivering a refined and usable energy product to that location.
The fuel lifecycle begins where the raw feedstock is extracted from the well or
mine and ends where the fuel is consumed to power a vehicle, appliance, or other
technology.
The Greenhouse Gas (GHG) footprint of propane is relatively small compared to
other fuels in terms of total emissions and emissions per unit of energy consumed.
Figure 1 shows the relative CO2 emission rates for various fuels, and propane has
the lowest emission rate of the major energy sources, with the exception of natural
gas. Electricity is included in this chart based on the average U.S. emissions of
the power generation industry.
Emissions released at the point of use are termed end-use emissions, while those
emissions that occur along the delivery pathway are termed upstream emissions.
Upstream emissions include all emissions resulting from the recovery, processing,
and transport of fuel to the point of delivery to the end-user.
Energy use is not the only source of upstream emissions. Other production
processes also release greenhouse gases. For example, the growing of crops for
biofuels production requires the application of nitrogen fertilizer, which causes
the formation of nitrogen oxide, while natural gas refining causes the release of
fugitive emissions of methane. These processes have been quantified by the
Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET)
model, making it a valuable tool for comparative lifecycle analyses of fuel
systems.
The inclusion of upstream emissions in an analytical comparison of different fuel
options can have a significant impact on the results. Limiting the comparison to
end-use emissions only, for example, can give the impression that electricity,
with zero end-use emissions, is an energy source with no greenhouse gas emissions.
Limiting the evaluation to end-use emissions only would mask the very large
fraction of upstream emissions caused by the combustion of fossil fuels for the
purpose of electricity generation.
Why Propane?
- Propane exhaust creates 60 to 70 percent less smog-producing hydrocarbons than
gasoline (Southwest Research Institute).
- Compared to gasoline, propane yields 12 percent less carbon dioxide, about 20
percent less nitrogen oxide, and as much as 60 percent less carbon monoxide (World
Liquid Propane Gas Association, January 2003; California Energy Commission, January
2003).
- Propane cuts emissions of toxins and carcinogens like benzene and toluene by up
to 96 percent compared to gasoline (Southwest Research Institute).
- Propane’s octane rating is 104, while premium grade gasoline’s is only 91 to 92,
which allows for a higher compression ratio in the engine and greater engine
efficiency. This leads to significant reductions in exhaust emissions like carbon
monoxide.
- Propane is listed as an approved alternative fuel in the 1990 Clean Air Act and
the Energy Policy Act of 1992.
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