Overview of Greenhouse Gases
Nitrous Oxide Emissions
|Lifetime in Atmosphere||114 years|
|Global Warming Potential (100-year)||298|
U.S. Nitrous Oxide Emissions, By Source
In 2013, nitrous oxide (N2O) accounted for about 5% 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 114 years before being removed by a sink or destroyed through chemical reactions. The impact of 1 pound of N2O on warming the atmosphere is almost 300 times that of 1 pound of carbon dioxide.
Globally, about 40% of total N2O emissions come from human activities.  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 74% of total U.S. N2O emissions in 2013. Nitrous oxide is also emitted during the breakdown of nitrogen in livestock manure and urine, which contributed to 5% of N2O emissions in 2013.
- 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.
Emissions and Trends
Nitrous oxide (N2O) emissions in the United States have increased by about 8% between 1990 and 2013. 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 18% higher in 2013 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. 
U.S. Nitrous Oxide Emissions, 1990-2013
Reducing Nitrous Oxide Emissions
There are a number of ways to reduce emissions of nitrous oxide (N2O). Some examples are discussed below. To learn more about opportunities to reduce non-CO2 greenhouse gases, and the costs of reduction technologies, see the EPA report Global Mitigation of Non-CO2 Greenhouse Gases: 2010-2030 and Mitigation of Non-CO2 Greenhouse Gases in the United States: 2010-2030 (PDF, 46pp, 9.47MB)
|Emissions Source||Examples of How Emissions Can be Reduced|
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,  as well as following better manure management practices.
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.
Global Warming Potential Describes Impact of Each Gas
Certain greenhouse gases (GHGs) are more effective at warming Earth ("thickening the blanket") than others.The two most important characteristics of a GHG in terms of climate impact are how well the gas absorbs energy (preventing it from immediately escaping to space), and how long the gas stays in the atmosphere.
The Global Warming Potential (GWP) for a gas is a measure of the total energy that a gas absorbs over a particular period of time (usually 100 years), compared to carbon dioxide. The larger the GWP, the more warming the gas causes. For example, methane's 100-year GWP is 21, which means that methane will cause 21 times as much warming as an equivalent mass of carbon dioxide over a 100-year time period.
- Carbon dioxide (CO2) has a GWP of 1 and serves as a baseline for other GWP values. CO2 remains in the atmosphere for a very long time - changes in atmospheric CO2 concentrations persist for thousands of years.
- Methane (CH4) has a GWP more than 20 times higher than CO2 for a 100-year time scale. CH4 emitted today lasts for only about a decade in the atmosphere, on average. However, on a pound-for-pound basis, CH4 absorbs more energy than CO2, making its GWP higher.
- Nitrous Oxide (N2O) has a GWP 300 times that of CO2 for a 100-year timescale. N2O emitted today remains in the atmosphere for more than 100 years, on average.
Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO2.
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 NRC (2010). Advancing the Science of Climate Change . National Research Council. The National Academies Press, Washington, DC, USA.
*Global Warming Potential (GWP) values are from the U.S. Inventory of Greenhouse Gas Emissions and Sinks. United Nations guidance currently requires national inventories to use GWPs from the IPCC???s Second Assessment Report.