4. Measurement methods

Operators of certain industrial plants are often required to measure their own nitrogen oxide emissions on an ongoing basis, as this is an integral part of their process.

In practice, in combustion fumes, excluding nitrous oxide N ₂ O, a stable compound, the NO ₂ concentration represents less than 5% of the total NO _x concentration and the measurement of NO alone may suffice. However, in other cases (gas turbine fumes in particular), the presence of NO ₂ is no longer negligible, then requiring measurement of the sum of NO and NO ₂ .

In these cases, where NO ₂ measurement...