A closely related molecule, nitrous oxide N 2 O , is a significant greenhouse gas that plays a role in global climate change. Nitrogen oxides form when oxygen and nitrogen from the air interact during a high-temperature combustion event.
These conditions occur in car engines and fossil fuel-powered electricity plants. Diesel engines, in particular, produce large amounts of nitrogen oxides. This is due to the combustion features characteristic of this type of engine, including their high operating pressures and temperatures, especially when compared to gasoline engines. In addition, diesel engines allow excess oxygen to exit the cylinders, diminishing the effectiveness of catalytic converters which prevent the release of most NOx gases in gasoline engines.
NOx gases play an important role in the formation of smog, producing the brown haze often observed over cities, particularly during the summer. During exposure to UV rays in sunlight and heat, NOx molecules interact with volatile organic compounds VOC and form ground-level or tropospheric ozone O 3.
Ozone at the ground level is a serious pollutant, unlike the protective ozone layer much higher up in the stratosphere. In the presence of rain, nitrogen oxides form nitric acid, contributing to the problem of acid rain. Additionally, NOx deposition in the oceans provides phytoplankton with nutrients , worsening the issue of red tides and other harmful algal blooms. Nitrogen oxides, nitric acid, and ozone can all readily enter the lungs, where they create serious damage to delicate lung tissue.
Even short-term exposure can irritate the lungs of healthy people. For those with medical conditions like asthma, just a short time spent breathing these pollutants has been shown to increase the risks of an emergency room visit or hospital stay.
For these residents—especially the very young and elderly—this air pollution can lead to respiratory diseases such as emphysema and bronchitis. NOx pollution can also worsen asthma and heart disease and is tied to elevated risks of premature death. In order to transform public opinion about diesel cars, Volkswagen marketed the diesel engines in their fleet of cars as new and clean-burning.
They said it was a "new era of diesel" and offered their vehicles as alternatives to hybrid cars, which were gobbling up bigger chunks of the market share. There were concerns over the cars' nitrogen oxide emissions, but those were appeased as the little Volkswagen diesel engines met the stringent requirements policed by the U.
Somehow, few other car companies seemed to be able to design and produce their own powerful but thrifty and clean diesel engines. The pie chart below shows that road transport and energy production are the greatest sources of NOx emissions in the EU during The anticipated relative proportion of emissions of NOx, from vehicles and gas boilers in the City during , is shown in the pie chart below.
A very similar picture is predicted for NOx mainly impacts on respiratory conditions causing inflammation of the airways at high levels. Long term exposure can decrease lung function, increase the risk of respiratory conditions and increases the response to allergens. NOx also contributes to the formation of fine particles PM and ground level ozone, both of which are associated with adverse health effects.
High levels of NOx can have a negative effect on vegetation, including leaf damage and reduced growth. It can make vegetation more susceptible to disease and frost damage. A study of the effect of nitrogen dioxide and ammonia NH3 on the habitat of Epping Forest has revealed that pollution is likely to be significantly influencing ecosystem health in the forest. The study demonstrated that local traffic emissions contribute substantially to exceeding the critical levels and critical loads in the area.
NOx also reacts with other pollutants in the presence of sunlight to form ozone which can damage vegetation at high concentrations. Notes: Critical Level is the threshold level for the atmospheric concentration of a pollutant above which harmful direct effects can be shown on a habitat or species. Critical Load is the threshold level for the deposition of a pollutant above which harmful indirect effects can be shown on a habitat or species.
In some instances the limits were exceeded by significant amounts. Qin, G. Plattner, M. Tignor, S. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. In , methane CH 4 accounted for about 10 percent of all U. Human activities emitting methane include leaks from natural gas systems and the raising of livestock. Methane is also emitted by natural sources such as natural wetlands. In addition, natural processes in soil and chemical reactions in the atmosphere help remove CH 4 from the atmosphere.
Methane's lifetime in the atmosphere is much shorter than carbon dioxide CO 2 , but CH 4 is more efficient at trapping radiation than CO 2. Pound for pound, the comparative impact of CH 4 is 25 times greater than CO 2 over a year period. Globally, percent of total CH 4 emissions come from human activities. Methane is also emitted from a number of natural sources.
Natural wetlands are the largest source, emitting CH 4 from bacteria that decompose organic materials in the absence of oxygen. Smaller sources include termites, oceans, sediments, volcanoes, and wildfires. To find out more about the role of CH 4 in warming the atmosphere and its sources, visit the Climate Change Indicators page. Methane emissions in the United States decreased by 15 percent between and During this time period, emissions increased from sources associated with agricultural activities, while emissions decreased from sources associated with landfills, coal mining, and from natural gas and petroleum systems.
There are a number of ways to reduce CH 4 emissions. Some examples are discussed below. EPA has a series of voluntary programs for reducing CH 4 emissions, in addition to regulatory initiatives. EPA also supports the Global Methane Initiative , an international partnership encouraging global methane reduction strategies.
Upgrading the equipment used to produce, store, and transport oil and natural gas can reduce many of the leaks that contribute to CH 4 emissions. Methane from coal mines can also be captured and used for energy. Methane from manure management practices can be reduced and captured by altering manure management strategies.
Additionally, modifications to animal feeding practices may reduce emissions from enteric fermentation. Because CH 4 emissions from landfill gas are a major source of CH 4 emissions in the United States, emission controls that capture landfill CH 4 are an effective reduction strategy. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. Averyt, M. Tignor and H. 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.
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