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NO x 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. [ 1 ] [ 2 ] [ 3 ] In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution.
Nitric oxide (nitrogen oxide or nitrogen monoxide [1]) is a colorless gas with the formula NO.It is one of the principal oxides of nitrogen.Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula (• N=O or • NO).
Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral. Nitric oxide (NO), nitrogen(II) oxide, or ...
Nitrogen dioxide is a reddish-brown gas with a pungent, acrid odor above 21.2 °C (70.2 °F; 294.3 K) and becomes a yellowish-brown liquid below 21.2 °C (70.2 °F; 294.3 K). It forms an equilibrium with its dimer , dinitrogen tetroxide ( N 2 O 4 ), and converts almost entirely to N 2 O 4 below −11.2 °C (11.8 °F; 261.9 K).
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NO x) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. [1] EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders .
Ground-level ozone (O 3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas.
x level in the exhaust gas (before catalytic converter, after catalytic converter, and possibly between catalytic converters if there is more than one), current ammonia filling level, [11] engine operating temperature and speed. [12]
The term NO x represents several forms of nitrogen oxides such as NO (nitric oxide), NO 2 (nitrogen dioxide) and N 2 O (nitrous oxide, also known as laughing gas).In a gasoline engine, NO is the most common form of NO x at around 93%, while NO 2 is around 5% and the rest is N 2 O.