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Climate Change

Overview of Greenhouse Gases

Nitrous Oxide Emissions

photo of nitrous oxide molecule
Properties of Nitrous Oxide
Chemical Formula N2O
Lifetime in Atmosphere 114 years
Global Warming Potential (100-year) 310
U.S. Nitrous Oxide Emissions, By Source
Pie chart of U.S. nitrous oxide emissions by source. 75 percent is from agricultural soil management, 6 percent from industry or chemical production,  5 percent from stationary combustion, 5 percent from other sources, 5 percent from manure management, and 4 percent from transportation.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012.

In 2012, nitrous oxide (N2O) accounted for about 6% of all U.S. greenhouse gas emissions from human activities. Nitrous oxide is naturally present in the atmosphere as part of the Earth's nitrogen cycle, and has a variety of natural sources. However, human activities such as agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere. Nitrous oxide molecules stay in the atmosphere for an average of 120 years before being removed by a sink or destroyed through chemical reactions. The impact of 1 pound of N2O on warming the atmosphere is over 300 times that of 1 pound of carbon dioxide.

Globally, about 40% of total N2O emissions come from human activities. [1] Nitrous oxide is emitted from agriculture, transportation, and industry activities, described below.

  • Agriculture. Nitrous oxide is emitted when people add nitrogen to the soil through the use of synthetic fertilizers. Agricultural soil management is the largest source of N2O emissions in the United States, accounting for about 75% of total U.S. N2O emissions in 2012. Nitrous oxide is also emitted during the breakdown of nitrogen in livestock manure and urine, which contributed to 4% of N2O emissions in 2012.
  • Transportation. Nitrous oxide is emitted when transportation fuels are burned. Motor vehicles, including passenger cars and trucks, are the primary source of N2O emissions from transportation. The amount of N2O emitted from transportation depends on the type of fuel and vehicle technology, maintenance, and operating practices.
  • Industry. Nitrous oxide is generated as a byproduct during the production of nitric acid, which is used to make synthetic commercial fertilizer, and in the production of adipic acid, which is used to make fibers, like nylon, and other synthetic products.

Nitrous oxide emissions occur naturally through many sources associated with the nitrogen cycle, which is the natural circulation of nitrogen among the atmosphere, plants, animals, and microorganisms that live in soil and water. Nitrogen takes on a variety of chemical forms throughout the nitrogen cycle, including N2O. Natural emissions of N2O are mainly from bacteria breaking down nitrogen in soils and the oceans. Nitrous oxide is removed from the atmosphere when it is absorbed by certain types of bacteria or destroyed by ultraviolet radiation or chemical reactions.

To find out more about the role of N2O in warming the atmosphere and its sources, visit the Causes of Climate Change page and the Greenhouse Gas Indicators page in the Science section.

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Nitrous oxide (N2O) emissions in the United States have increased by about 3% between 1990 and 2012. This increase in emissions is due in part to annual variation in agricultural soil emissions, and an increase in emissions from the electric power sector. Nitrous oxide emissions from agricultural soils have varied during this period and were about 9% higher in 2012 than in 1990.

Going forward, N2O emissions are projected to increase by 5% between 2005 and 2020, driven largely by increases in emissions from agricultural activities. [2]

U.S. Nitrous Oxide Emissions, 1990-2012
Line graph that shows U.S. nitrous oxide emissions from 1990 to 2012. In 1990 nitrous oxide emissions were at approximately 400 million metric tons of carbon dioxide equivalents. The emissions increase to a peak in 1996 around 470 million metric tons of carbon dioxide equivalents, then decrease to just above 400 million metric tons of carbon dioxide equivalents in 2012.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012.

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Reducing Nitrous Oxide Emissions

There are a number of ways to reduce emissions of nitrous oxide (N2O), discussed below.

Examples of Reduction Opportunities for Nitrous Oxide Emissions
Emissions Source Examples of How Emissions Can be Reduced

Agriculture

The application of fertilizers accounts for the majority of N2O emissions. Emissions can be reduced by reducing nitrogen-based fertilizer applications and applying fertilizers more efficiently, [3] as well as following better manure management practices.

Transportation

  • Nitrous oxide is a byproduct of fuel combustion, so reducing mobile fuel consumption in motor vehicles can reduce transportation emissions.
  • Additionally, the introduction of pollution control technologies, such as catalytic converters to reduce exhaust pollutants from passenger cars, can also reduce emissions of N2O.

Industry

  • Nitrous oxide is generally emitted from industry through fossil fuel combustion so technological upgrades and fuel switching are effective ways to reduce industry emissions of N2O.
  • Production of adipic acid results in N2O emissions that can be reduced through technological upgrades.

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References

1. EPA (2010). Methane and Nitrous Oxide Emissions from Natural Sources (PDF). U.S. Environmental Protection Agency, Washington, DC, USA.

2. U.S. Department of State (2007). Projected Greenhouse Gas Emissions. In: Fourth Climate Action Report to the UN Framework Convention on Climate Change . U.S. Department of State, Washington, DC, USA.

3. EPA (2005). Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture . U.S. Environmental Protection Agency, Washington, DC, USA.

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