A nitrogen oxide sensor or sensor is typically a high-temperature device built to detect nitrogen oxides in combustion environments such as an automobile, truck tailpipe or smokestack. Overview The term represents several forms of nitrogen oxides such as NO (nitric oxide), NO2 (nitrogen dioxide) and N2O (nitrous oxide, also known as laughing gas). In a gasoline engine, NO is the most common form of at around 93%, while NO2 is around 5% and the rest is N2O. There are other forms of such as N2O4 (the dimer of NO2), which only exists at lower temperatures, and N2O5, for example. Meanwhile, for diesel engines, the emissions situation is different. Owing to their much higher combustion temperatures (resulting from their high cylinder compression ratios as well as turbocharging or supercharging), diesel engines produce much higher engine-out emissions than spark-ignition gasoline engines. The recent availability of Selective catalytic reduction (SCR) allows properly equipped diesel engines to emit similar values of at the tailpipe compared to a typical gasoline engine with a 3-way catalyst. The SCR changes the harmful nitrogen oxides by adding the solution AdBlue which reduces environmental pollution and protects the exhaust system. In addition, the diesel oxidation catalyst significantly increases the fraction of NO2 in "" by oxidizing over 50% of NO using the excess oxygen in the diesel exhaust gases. The drive to develop a sensor arises from environmental factors. gases can cause various problems such as smog and acid rain. Many governments around the world have passed laws to limit their emissions (along with other combustion gases such as SOx (oxides of sulfur), CO (carbon monoxide) and CO2 (carbon dioxide) and hydrocarbons). Companies have realized that one way of minimizing emissions is to first detect them and then to employ some sort of feedback loop in the combustion process, thereby enabling the minimization of production by, for example, combustion optimization or regeneration of traps. Therefore, in many applications with exhaust-gas treatment systems, one NOx sensor is used upstream of the exhaust-gas treatment system (upstream) and a second sensor is used downstream of the exhaust-gas treatment system. The upstream sensor is used for the aforementioned feedback loop. Meanwhile, the downstream sensor is used mainly to confirm that the legislated emissions limits have not been exceeded. Challenges Harsh environment Due to the high temperature of the combustion environment, only certain types of material can operate in situ. The majority of sensors