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Emissions of Greenhouse Gases Report
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Nitrous Oxide Emissions
Total Emissions | Agriculture | Energy Use | Industrial Sources | Waste Management |
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Total Emissions |
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U.S. nitrous oxide emissions in 2008 were 0.1 percent (0.4 MMTCO2e) above
their 2007 total (Table 21 below).
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Sources of U.S. nitrous oxide emissions include agriculture, energy use,
industrial processes, and waste management. The largest source is agriculture,
and the majority of agricultural emissions result from nitrogen fertilization
of agricultural soils (75.7 percent) and the management of animal waste
(24.0 percent). |
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Annual U.S. nitrous oxide emissions rose from 1990 to 1994, then fell from
1994 to 2003 (Figure 20 on right). They rose sharply from 2003 to 2008, largely
as a result of increased use of synthetic fertilizers, which grew by more
than 30 percent from 2005 to 2008.
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Since 2005, when the Renewable Fuels Standard was signed into law, U.S.
ethanol production has more than doubled (a 130-percent increase
from 2005 to 2008). Nearly all U.S. ethanol production is from corn, and
with corn production rising by 8.9 percent since 2005, the percentage used
for ethanol production also has risen, from 16.1 percent to 21.1 percent
of total U.S. corn production. As the demand for corn has increased, use
of synthetic fertilizer (a nitrous oxide emitter that is used most heavily
in corn production) has risen by 8.2 percent. |
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figure data
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| Agriculture |
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Agricultural sources, at 217.9 MMTCO2e, account for 73 percent of U.S.
nitrous oxide emissions. Nitrous oxide emissions from agricultural sources
increased by 1.9 percent (4.0 MMTCO2e) from 2007 to 2008 (Table 22 below). |
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Three-quarters (165.0 MMTCO2e) of U.S. agricultural emissions of nitrous
oxide in 2008 is attributable to nitrogen fertilization of soils (Figure
21 on right), including 145.2 MMTCO2e from direct emissions and 19.8 MMTCO2e from
indirect emissions. |
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Microbial denitrification of solid waste from domestic animals in the United
States, primarily cattle, emitted 52.3 MMTCO2e of nitrous oxide in 2008.
The amount released is a function of animal size and manure production,
the amount of nitrogen in the waste, and the method of managing the waste.
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Agricultural emissions of nitrous oxide are 23 to 28 percent lower in all
years in the 2008 inventory than in the 2007 inventory, following the IPCC’s
downward revisions of direct and indirect emissions factors for nitrogen
from the fertilization of agricultural soils. |
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figure data
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| Energy Use |
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Emissions from energy sources made up about 21 percent of total U.S. nitrous
oxide emissions in 2008. Nitrous oxide is a byproduct of fuel combustion
in mobile and stationary sources (Figure 22).
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More than three-quarters of U.S. nitrous oxide emissions from energy use
can be traced to mobile sources—motor vehicles, primarily passenger cars
and light trucks (Table 23). Emissions from mobile sources dropped by 4.8
percent (2.4 MMTCO2e) from 2007 to 2008, primarily because of a 5.2-percent
decrease in emissions from passenger cars and light trucks. Vehicle miles
traveled by passenger vehicles were 3.3 percent lower in 2008 than in 2007,
as a result of higher gasoline prices and economic uncertainty. |
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Nitrous oxide emissions from stationary combustion sources result predominantly
from the burning of coal at electric power plants (9.2 MMTCO2e, or 61.2
percent of all nitrous oxide from stationary combustion). |
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| Industrial Sources |
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figure data
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| Waste Management |
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figure data
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Notes and Sources |
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