Measurement methods
NOx (Nitrogen oxides)

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 N₂O, a stable compound, the NO₂ 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 NO₂ is no longer negligible, then requiring measurement of the sum of NO and NO₂.

In these cases, where NO₂ measurement is necessary, we actually operate indirectly by transforming the NO₂ into NO in a thermal and/or catalytic converter (often a furnace filled with copper and molybdenum catalyst, heated to between 200 and 300°C) located upstream of the analyzer. In...