Nitrous Oxide

Figure Data

Estimated U.S. anthropogenic emissions of nitrous oxide in 2005 totaled 366.6 MMTCO₂e, or 1.2 MMT nitrous oxide. Nitrous oxide emissions represented 5.1 percent of total U.S. greenhouse gas emissions in 2005 and were 1.9 percent (6.7 MMTCO₂e) above the 2004 level of 359.9 MMTCO₂e. Most of the increase from 2004 can be attributed to increased emissions from agricultural sources, which rose by 7.0 MMTCO₂e in 2005. Emissions from waste management contributed about 1 percent to the total growth from 2004 to 2005, whereas emissions from industrial sources were 5.3 percent lower in 2005 than in 2004 (Table ES5 and Figure ES5). 

Agriculture 

Agricultural sources, at 279.9 MMTCO₂e, accounted for 76 percent of total U.S. nitrous oxide emissions in 2005. Agricultural emissions in 2005 were 2.6 percent above the 2004 total of 272.9 MMTCO₂e, primarily as the result of an increase of 2.9 percent (6.2 MMTCO₂e) in emissions from the nitrogen fertilization of agricultural soils. Emissions from nitrogen fertilization, at 218.1 MMTCO₂e, accounted for 60 percent of nitrous oxide emissions from agriculture in 2005. Emissions from the solid waste of domesticated animals, at 61.2 MMTCO₂e, made up 22 percent of agricultural nitrous oxide emissions in 2005, and burning of crop residues produced another 0.6 MMTCO₂e. Total U.S. emissions of nitrous oxide from agriculture sources have increased by 12.3 percent since 1990. 

Energy Use 

U.S. nitrous oxide emissions associated with fossil fuel combustion in 2005 were 67.3 MMTCO₂e, or 18 percent of total nitrous oxide emissions. Most of the energy-related emissions of nitrous oxide in 2005 (78 percent or 52.6 MMTCO₂e) were from mobile sources, principally, motor vehicles equipped with catalytic converters. The remainder (22 percent or 14.7 MMTCO₂e) was from stationary source combustion of fossil fuels. Nitrous oxide emissions from energy sources have increased by 32 percent since 1990. 

Industrial Processes and Waste Management 

Industrial processes and waste management facilities were responsible for 3.6 percent and 1.6 percent, respectively, of total U.S. nitrous oxide emissions in 2005. Industrial process emissions in 2005 (13.2 MMTCO₂e) were 5.3 percent below the 2004 level of 14.0 MMTCO₂e. Industrial process emissions have fallen by 54 percent since 1990 due to decreases in nitrous oxide emissions from the manufacture of adipic acid. 

Nitrous oxide emissions from waste management facilities in 2005 (6.2 MMTCO₂e) increased by 1.1 percent from the 2004 level of 6.1 MMTCO₂e. Most of the 2005 emissions (5.8 MMTCO₂e) were from human sewage in wastewater and the remainder from waste combustion. Nitrous oxide emissions from waste management facilities have increased by 26 percent since 1990.

Notes