How does a chemiluminescence NOx analyzer work?

• A. They measure electrical conductivity.
• B. NOx analyzers typically convert all NOx to NO with a converter and measure the resulting chemiluminescent light from the reaction of NO with ozone.
• C. They count NOx molecules directly.
• D. They measure infrared absorption.

Answer: (B)

Chemiluminescence NOx analysis relies on detecting light produced when NO reacts with ozone. To measure all the NOx forms present, the sample is passed through a converter that transforms all NOx species (like NO2 and other oxidized forms) into NO. This way, the subsequent reaction with ozone produces a chemiluminescent glow, and the light intensity is proportional to the amount of NO in the stream. Since that NO came from all NOx species after conversion, the signal represents the total NOx in the sample. In practice, some instruments compare signals with the converter on and off to separate NO from NOx, but the core idea is converting NOx to NO and measuring the resulting light from NO + O3. Other options don’t describe this light-emission reaction or the role of conversion: electrical conductivity isn’t the basis of this method, counting molecules directly isn’t how chemiluminescence works, and infrared absorption involves a different principle altogether.