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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 2007 were 2.2 percent (8.2 MMTCO2e) above
their 2006 total (see Table 21 below). |
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Rising demand for corn-based ethanol in 2007 led to an 18-percent increase
in U.S. corn production and a 19-percent drop in soybean production. As
a result, the use of synthetic fertilizer (a nitrous oxide emitter), which
is required for corn production, rose by 9.6 percent. (Soybeans do not
need synthetic fertilizer, because they fix nitrogen in the soil.) |
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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 and the disposal of animal waste. |
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Annual U.S. nitrous oxide emissions rose from 1990 to 1994, then fell from
1994 to 2003 (see Figure 18 on right). They began rising sharply from 2003 to 2007,
largely as a result of increased use of synthetic fertilizers. |
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figure data
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| Agriculture |
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Agricultural sources, at 292.4 MMTCO2e, account for more than three-quarters
of all U.S. nitrous oxide emissions. U.S. nitrous oxide emissions from
agricultural sources increased by 2.4 percent from 2006 to 2007 (see Table
22 below). |
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More than three-quarters (229.6 MMTCO2e) of U.S. agricultural emissions
of nitrous oxide in 2007 is attributable to nitrogen fertilization of soils
(see Figure 19 on right), including 174.0 MMTCO2e from direct emissions and 55.7 MMTCO2e
from indirect emissions. |
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Microbial denitrification of solid waste from domestic animals in the United
States, primarily cattle, emitted 62.2 MMTCO2e of nitrous oxide in 2007.
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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figure data
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| Energy Use |
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Emissions from energy sources made up almost 20 percent of total U.S. nitrous
oxide emissions in 2007. Nitrous oxide is a byproduct of fuel combustion
in mobile and stationary sources (see Figure 20 on right). |
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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 (see Table 23 below). Emissions from mobile sources increased by
1.8 percent from 2006 to 2007, primarily because of a 12.9-percent increase
in emissions from off-road vehicles (included in “Other Mobile Sources”). |
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Nitrous oxide emissions from stationary combustion sources are dominated
by coal-fired generation at electric power plants. |
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figure data
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| Industrial Sources |
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U.S. nitrous oxide emissions from industrial sources in 2007, at 14.0 MMTCO2e,
were unchanged from 2006 (see Table 24 below). |
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The two industrial sources of nitrous oxide emissions are production of
adipic acid and production of nitric acid. |
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A large decline in nitrous oxide emissions from industrial processes since
1996 (see Figure 21 on right) is a result of emissions control technology at three of
the four adipic acid plants operating in the United States. Adipic acid
is a fine white power used primarily in the manufacture of nylon fibers
and plastics. The three companies operating the U.S. plants manufacture
adipic acid by oxidizing a ketone-alcohol mixture with nitric acid. The
chemical reaction releases nitrous oxide emissions. |
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Nitric acid, a primary ingredient in fertilizers, usually is manufactured
by oxidizing ammonia with a platinum catalyst. The oxidation process releases
nitrous oxide emissions. |
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figure data
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| Waste Management |
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Emissions from residential and commercial wastewater account for nearly
all U.S. nitrous oxide emissions from waste management. The remainder is
associated with the combustion of municipal solid waste (see Figure 22 on right and
Table 25 belos).
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Estimates of nitrous oxide emissions from wastewater are scaled to population
size and per-capita intake of protein. |
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Nitrous oxide is emitted from wastewater that contains nitrogen-based organic
materials, such as those found in human or animal waste. Factors that influence
the amount of nitrous oxide generated from wastewater include temperature,
acidity, biochemical oxygen demand, and nitrogen concentration. |
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figure data
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