|
Nitrous Oxide U.S. nitrous oxide emissions decreased by 1.1 percent from 2001 to 2002, to 1.1 million metric tons of nitrous oxide or 333.1 million metric tons carbon dioxide equivalent (4.9 percent of total U.S. greenhouse gas emissions). The 2002 decline in nitrous oxide emissions resulted from decreases in emissions from agricultural sources. Since 1990, U.S. nitrous oxide emissions have fallen by 0.2 percent. Emissions estimates for nitrous oxide are more uncertain than those for either carbon dioxide or methane. Nitrous oxide is not systematically measured, and for many sources of nitrous oxide emissions, including nitrogen fertilization of soils and motor vehicles, a significant number of assumptions are required for the derivation of emissions estimates.
U.S. nitrous oxide emissions include two large categories of sources, agriculture and energy use, and two smaller categories, industrial processes and waste management (Figure ES5). Agricultural sources, at 791 thousand metric tons of nitrous oxide or 234.2 million metric tons carbon dioxide equivalent, account for 70.3 percent of total U.S. nitrous oxide emissions. Emissions associated with nitrogen fertilization of soils, at 583 thousand metric tons or 172.5 million metric tons carbon dioxide equivalent, account for 73.7 percent of nitrous oxide emissions from agriculture. Emissions from the solid waste of animals, at 207 thousand metric tons or 61.2 million metric tons carbon dioxide equivalent, make up 26.1 percent of agricultural nitrous oxide emissions. Nitrous oxide emissions from agriculture have decreased by 2.8 percent since 1990. U.S. nitrous oxide emissions associated with fossil fuel combustion in 2002 were 0.3 million metric tons of nitrous oxide, or 23.4 percent of total nitrous oxide emissions. Of these energy-related emissions, 81.4 percent comes from mobile sources, principally motor vehicles equipped with catalytic converters. The remainder comes from stationary source combustion of fossil fuels. Nitrous oxide emissions from energy sources have increased by 31.5 percent since 1990. Industrial processes and wastewater treatment facilities are responsible for 6.2 percent of total nitrous oxide emissions. Industrial process emissions increased from 47 thousand metric tons (14.0 million metric tons carbon dioxide equivalent) in 2001 to 50 thousand metric tons (14.9 million metric tons carbon dioxide equivalent) in 2002. This represents the first increase in industrial nitrous oxide emissions since 1996. The increase can be attributed to the leveling off of emissions reductions from adipic acid production, as well as a slight increase in emissions from nitric acid production. Emissions from wastewater treatment facilities were 20 thousand metric tons of nitrous oxide (6.0 million metric tons carbon dioxide equivalent), an increase of 0.3 thousand metric tons (0.1 million metric tons carbon dioxide equivalent) or 1.4 percent from 2001
Released: October 2003 |
