Chemiluminescence (chemiluminescence analyser)

Chemiluminescence is an analytical technique that quantifies a gas by measuring the light emitted when it undergoes a specific chemical reaction. In air monitoring its classic application is the NOₓ analyser: nitric oxide (NO) reacts with ozone to form excited NO₂, which emits light as it relaxes; the light intensity is proportional to the NO concentration, and NO₂ is measured by first converting it to NO. It is the NAAQS reference method for nitrogen oxides and is also used for ozone and ammonia measurement.

The technique is prized for being continuous, sensitive and specific — it gives real-time readings down to very low concentrations with little interference, which is why it underpins both manual reference monitoring and the automatic analysers in continuous ambient and stack monitoring systems. This contrasts with gravimetric particulate measurement, which is mass-based and not real-time.

For recyclers, chemiluminescence is the method behind the NO₂/NOₓ numbers in ambient air reports and behind the NOₓ channel of any continuous monitoring system. Since every combustion source on a recycling site — gensets, boilers, dryers, pyrolysis burners — emits NOₓ, the chemiluminescence-derived NO₂ figure is a routine parameter in the plant's air data.

The practical relevance is mostly interpretive: a recycler need not operate the instrument, but should understand that the NO₂/NOₓ values in monitoring reports come from a real-time, reference-grade method, and that an OCEMS on a large source will typically use chemiluminescence (or equivalent) for its NOₓ channel, transmitting live data to the SPCB. Knowing the method helps in reading and trusting the data, and in specifying credible monitoring when commissioning a plant.