What is NOx?

Answer 1

NOx is shorthand for "oxides of nitrogen", which are largely byproducts of infernal combustion. Inclusive of NO2, N2O, N2O5 and more. Naturally occurring NOx compounds are made high in the atmosphere, in the ozone layer (lower stratosphere), too. Whether or not they remain stable or decay to nitrogen, oxygen and/or ozone depends on how much water vapor is present there. Typically, NOx made up here does also not survive to reach the troposphere, since it is very chemically reactive (much like ozone). At the surface NOx is a product of combustion and can be emitted from internal combustion engines, furnace, boilers and heaters.