b'Power & Energy | Engineer InnovationNitrogen dioxide or NOx is a compound formed from nitrogen and oxygen as a result of the high temperatures generated during combustion processes. NOx is composed of oxygen and nitrogen, so the air entering the engine, consisting of 21 percent oxygen and 79 percent nitrogen, contains all the ingredients necessary to produce this pollutant. The only additional factor that is required is a temperature high enough to cause oxygen and nitrogen to combine. Although NOx can be created naturally, the vast majority of global NOx production is a consequence of combustion, from energy production and transportation NOx reacts with ammonia, moisture, and other compounds to form nitric acid vapor, which damages lung tissue and has a deleterious effect on breathing and respiration. NOx is also a key component of acid rain that has an environmental impact on forests and lakes. It also contributes to the formation of fine particles and ground-level ozone, both of which are associated with adverse health effects.Since the introduction of emission standards for gas turbines in the late 1970s, gas turbine manufacturers have implemented a variety of innovative solutions that both reduce the pollutants created during the combustion process and increase the amount removed through aftertreatment of exhaust gases. These measures have been highly successful in reducing the emission of harmful pollutants, particularlyIn the early 1980s, industrial gas turbines were routinely emitting 75ppm NOx. Today regulations in most countries require that emissions are limited to 25 ppm or less, and increasingly in Europe and the US even stricter NOx emission standards require maximum levels of 15 or even 10 ppm. In response to this, manufacturers such as Siemens Energy had largely achieved so-called single-digit NOx emissions in the latest generations of gas turbines ( 10 ppm).11'