Miller eds. Cambridge University Press. Cambridge, United Kingdom pp. In , nitrous oxide N 2 O accounted for about 7 percent of all U. Human activities such as agriculture, fuel combustion, wastewater management, and industrial processes are increasing the amount of N 2 O in the atmosphere.
Nitrous oxide is also naturally present in the atmosphere as part of the Earth's nitrogen cycle, and has a variety of natural sources. Nitrous oxide molecules stay in the atmosphere for an average of years before being removed by a sink or destroyed through chemical reactions.
The impact of 1 pound of N 2 O on warming the atmosphere is almost times that of 1 pound of carbon dioxide. 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 N 2 O.
Natural emissions of N 2 O 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 sources of N 2 O and its role in warming the atmosphere, visit the Climate Change Indicators page.
Nitrous oxide emissions in the United States have remained relatively flat between and Nitrous oxide emissions from mobile combustion decreased by 60 percent from to as a result of emission control standards for on-road vehicles.
Nitrous oxide emissions from agricultural soils have varied during this period and were about 9 percent higher in than in , primarily driven by increasing use of nitrogen fertilizers. The application of nitrogen fertilizers accounts for the majority of N 2 O emissions in the United States.
Emissions can be reduced by reducing nitrogen-based fertilizer applications and applying these fertilizers more efficiently, 3 as well as modifying a farm's manure management practices. Additionally, the introduction of pollution control technologies e. Production of adipic acid results in N 2 O emissions that can be reduced through technological upgrades. Greenhouse Gas Mitigation Potential in U. Forestry and Agriculture. Unlike many other greenhouse gases, fluorinated gases have no natural sources and only come from human-related activities.
They are emitted through their use as substitutes for ozone-depleting substances e. Many fluorinated gases have very high global warming potentials GWPs relative to other greenhouse gases, so small atmospheric concentrations can have disproportionately large effects on global temperatures. They can also have long atmospheric lifetimes—in some cases, lasting thousands of years.
Like other long-lived greenhouse gases, most fluorinated gases are well-mixed in the atmosphere, spreading around the world after they are emitted. Many fluorinated gases are removed from the atmosphere only when they are destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by human activities.
The largest sources of fluorinated gas emissions are described below. To find out more about the role of fluorinated gases in warming the atmosphere and their sources, visit the Fluorinated Greenhouse Gas Emissions page. Overall, fluorinated gas emissions in the United States have increased by about 86 percent between and This increase has been driven by a percent increase in emissions of hydrofluorocarbons HFCs since , as they have been widely used as a substitute for ozone-depleting substances.
Emissions of perfluorocarbons PFCs and sulfur hexafluoride SF 6 have actually declined during this time due to emission reduction efforts in the aluminum production industry PFCs and the electricity transmission and distribution industry SF 6. Because most fluorinated gases have a very long atmospheric lifetime, it will take many years to see a noticeable decline in current concentrations.
Jump to site search. You do not have JavaScript enabled. Please enable JavaScript to access the full features of the site or access our non-JavaScript page. Issue 5, From the journal: Physical Chemistry Chemical Physics. You have access to this article.
Please wait while we load your content Something went wrong. Try again? Cited by. Unable to display preview. Download preview PDF. Skip to main content. This service is more advanced with JavaScript available. Advertisement Hide. Nitrogen comes out of solution much more quickly causing a more aggressive foaming reaction. This more aggressive reaction has both positive and negative aspects.
On the positive side, nitrogen will tend to create a higher cell density which also translates to an overall smaller cell size. In addition nitrogen will create cell structure in thinner walls than will CO2.
The images below show a clarified random copolymer PP molded in a container with a wall thickness of 0. This occurs as the polymer freezes before the CO2 can cause the cells to grow while the nitrogen rapids expands the cells. The negative aspect of the aggressive foaming seen with nitrogen is that nitrogen will typically produce a more pronounce surface change than CO2.
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By: Levi Kishbaugh. Background: The initial development work on microcellular foaming was done using a batch process.
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