NOx: Құрамы мен әсері

Term for nitric oxide and nitrogen dioxide
DISPLAYTITLE:NOx

In atmospheric chemistry, is shorthand for nitric oxide and nitrogen dioxide (|NO2), the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone. gases are usually produced from the reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as in car engines. In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution. gases are also produced naturally by lightning. does not include nitrous oxide (|N2O), and high global warming potential. is defined as the sum of plus the compounds produced from the oxidation of which include nitric acid, nitrous acid (HONO), dinitrogen pentoxide (|N2O5), peroxyacetyl nitrate (PAN), alkyl nitrates (|RONO2), peroxyalkyl nitrates (|ROONO2), the nitrate radical (|NO3), and peroxynitric acid (|HNO4).

When and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog, a significant form of air pollution. The presence of photochemical smog increases during the summer when the incident solar radiation is higher. The emitted hydrocarbons from industrial activities and transportation react with quickly and increase the concentration of ozone and peroxide compounds, especially peroxyacetyl nitrate (PAN). Children, people with lung diseases such as asthma, and people who work or exercise outside are particularly susceptible to adverse effects of smog such as damage to lung tissue and reduction in lung function.

It is estimated that transportation fuels cause 54% of the anthropogenic (i. e. human caused) The major source of production from nitrogen bearing fuels such as certain coals and oil, is the conversion of fuel bound nitrogen to during combustion. Although the complete mechanism is not fully understood, there are two primary pathways of formation. The first involves the oxidation of volatile nitrogen species during the initial stages of combustion. During the release and before the oxidation of the volatiles, nitrogen reacts to form several intermediaries which are then oxidized into NO. If the volatiles evolve into a reducing atmosphere, the nitrogen evolved can readily be made to form nitrogen gas, rather than The second pathway involves the combustion of nitrogen contained in the char matrix during the combustion of the char portion of the fuels. This reaction occurs much more slowly than the volatile phase. Only around 20% of the char nitrogen is ultimately emitted as , since much of the that forms during this process is reduced to nitrogen by the char, which is nearly pure carbon.

Nitrogen oxides are released during manufacturing of nitrogen fertilizers. Though nitrous oxide is emitted during its application, it is then reacted in atmosphere to form nitrogen oxides. This third source is attributed to the reaction of atmospheric nitrogen, |N2, with radicals such as C, CH, and |CH2 fragments derived from fuel, rather than thermal or fuel processes. Occurring in the earliest stage of combustion, this results in the formation of fixed species of nitrogen such as NH (nitrogen monohydride), NCN (diradical cyanonitrene), HCN (hydrogen cyanide), •|H2CN (dihydrogen cyanide) and •CN (cyano radical) which can oxidize to NO. In fuels that contain nitrogen, the incidence of prompt is comparatively small and it is generally only of interest for the most exacting emission targets.

There is strong evidence that respiratory exposure can trigger and exacerbate existing asthma symptoms, and may even lead to the development of asthma over longer periods of time. It has also been associated with heart disease, diabetes, birth outcomes, and all cause mortality, but these nonrespiratory effects are less well established. reacts with ammonia, moisture, and other compounds to form nitric acid vapor and related particles. reacts with volatile organic compounds in the presence of sunlight to form ozone. Ozone can cause adverse effects such as damage to lung tissue and reduction in lung function mostly in susceptible populations (children, elderly, asthmatics). Ozone can be transported by wind currents and cause health impacts far from the original sources. The American Lung Association estimates that nearly 50 percent of United States inhabitants live in counties that are not in ozone compliance. In South East England, ground level ozone pollution tends to be highest in the countryside and in suburbs, while in central London and on major roads NO emissions are able to "mop up" ozone to form and oxygen. also readily reacts with common organic chemicals, and even ozone, to form a wide variety of toxic products: nitroarenes, nitrosamines and also the nitrate radical some of which may cause DNA mutations. Recently another pathway, via , to ozone has been found that predominantly occurs in coastal areas via formation of nitryl chloride when comes into contact with salt mist. The direct effect of the emission of has positive contribution to the greenhouse effect. Instead of reacting with ozone in Reaction 3, NO can also react with |HO2* and organic peroxyradicals (|RO2*) and thus increase the concentration of ozone. Once the concentration of exceeds a certain level, atmospheric reactions result in net ozone formation. Since tropospheric ozone can absorb infrared radiation, this indirect effect of is intensifying global warming. There are also other indirect effects of that can either increase or decrease the greenhouse effect. First of all, through the reaction of NO with |HO2* radicals, •OH radicals are recycled, which oxidize methane molecules, meaning emissions can counter the effect of greenhouse gases. For instance, ship traffic emits a great amount of which provides a source of over the ocean. Then, photolysis of |NO2 leads to the formation of ozone and the further formation of hydroxyl radicals (·OH) through ozone photolysis. Since the major sink of methane in the atmosphere is by reaction with •OH radicals, the emissions from ship travel may lead to a net global cooling. However, in the atmosphere may undergo dry or wet deposition and return to land in the form of |HNO3/|NO3−. Through this way, the deposition leads to nitrogen fertilization and the subsequent formation of nitrous oxide (|N2O) in soil, which is another greenhouse gas. In conclusion, considering several direct and indirect effects, emissions have a negative contribution to global warming. in the atmosphere is removed through several pathways. During daytime, |NO2 reacts with hydroxyl radicals (·OH) and forms nitric acid (|HNO3), which can easily be removed by dry and wet deposition. Organic peroxyradicals (|RO2·) can also react with NO and |NO2 and result in the formation of organic nitrates. These are ultimately broken down to inorganic nitrate, which is a useful nutrient for plants. During nighttime, |NO2 and NO can form nitrous acid (HONO) through surface catalyzed reaction. Although the reaction is relatively slow, it is an important reaction in urban areas. While earlier studies suggested biodiesel could sometimes decrease and sometimes increase emissions, subsequent investigation has shown that blends of up to 20% biodiesel in USEPA approved diesel fuel have no significant impact on emissions compared with regular diesel. The state of California uses a special formulation of diesel fuel to produce less relative to diesel fuel used in the other 49 states. This has been deemed necessary by the California Air Resources Board (CARB) to offset the combination of vehicle congestion, warm temperatures, extensive sunlight, PM, and topography that all contribute to the formation of ozone and smog. CARB has established a special regulation for Alternative Diesel Fuels to ensure that any new fuels, including biodiesel, coming into the market do not substantially increase emissions. The reduction of emissions is one of the most important challenges for advances in vehicle technology. While diesel vehicles sold in the US since 2010 are dramatically cleaner than previous diesel vehicles, urban areas continue to seek more ways to reduce the formation of smog and ozone. formation during combustion is associated with a number of factors such as combustion temperature. As such, it can be observed that the vehicle drive cycle, or the load on the engine have more significant impact on emissions than the type of fuel used. This may be especially true for modern, clean diesel vehicles that continuously monitor engine operation electronically and actively control engine parameters and exhaust system operations to limit emission to less than 0.2 g/km. Low temperature combustion or LTC technology diesel trucks and in some diesel cars. The use of exhaust gas recirculation and catalytic converters in motor vehicle engines have significantly reduced vehicular emissions. was the main focus of the Volkswagen emissions violations. Other technologies such as flameless oxidation (FLOX) and staged combustion significantly reduce thermal in industrial processes. Bowin low technology is a hybrid of staged premixed radiant combustion technology with major surface combustion preceded by minor radiant combustion. In the Bowin burner, air and fuel gas are premixed at a ratio greater than or equal to the stoichiometric combustion requirement. Water Injection technology, whereby water is introduced into the combustion chamber, is also becoming an important means of reduction through increased efficiency in the overall combustion process. Alternatively, the water (e. g. 10 to 50%) is emulsified into the fuel oil before the injection and combustion. This emulsification can either be made in line (unstabilized) just before the injection or as a drop in fuel with chemical additives for long term emulsion stability (stabilized). Excessive water addition facilitates hot corrosion, which is the primary reason why dry low technologies are favored today besides the requirement of a more complex system.