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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.
The flames caused as a result of a fuel undergoing combustion (burning) Air pollution abatement equipment provides combustion control for industrial processes.. Combustion, or burning, [1] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.
In most hydrogen-fusing stars, including the Sun, a chemical cycle involved in stellar nucleosynthesis occurs which is known as a carbon-nitrogen-oxygen or . In addition to this cycle, stars also have a helium cycle. [1] Various cycles involving gas and dust have been found to occur in galaxies. [2]
Due to relatively weak N–O bonding, all nitrogen oxides are unstable with respect to N 2 and O 2, which is the principle behind the catalytic converter, and prevents the oxygen and nitrogen in the atmosphere from combusting.
When exposed to oxygen, nitric oxide converts into nitrogen dioxide: 2 • NO + O 2 → 2 • NO 2. This reaction is thought to occur via the intermediates ONOO • and the red compound ONOONO. [16] In water, nitric oxide reacts with oxygen to form nitrous acid (HNO 2). The reaction is thought to proceed via the following stoichiometry:
The oxygen cycle demonstrates how free oxygen is made available in each of these regions, as well as how it is used. The oxygen cycle is the biogeochemical cycle of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. [1]
This allows the gases to stratify by molecular weight, with the heavier ones, such as oxygen and nitrogen, present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.
Reactive nitrogen species act together with reactive oxygen species (ROS) to damage cells, causing nitrosative stress. Therefore, these two species are often collectively referred to as ROS/RNS. Reactive nitrogen species are also continuously produced in plants as by-products of aerobic metabolism or in response to stress. [3]