Which NOx measurement technique uses chemiluminescence detection?

Which NOx measurement technique uses chemiluminescence detection?

• A. Nondispersive infrared spectroscopy
• B. Chemiluminescence
• C. Pararosaniline
• D. Transmissometer

Answer: (B)

The technique that uses chemiluminescence detection for NOx relies on light produced during a chemical reaction. In this method, nitric oxide (NO) reacts with ozone (O3) to form an excited NO2 species (NO2*), which emits photons as it relaxes to its ground state. A photomultiplier or similar detector measures that light, and the signal is proportional to the NO concentration in the gas. To measure total NOx, the sample can first pass through a converter that converts NO2 to NO, so the detector’s signal represents all oxides of nitrogen as NO. This is why chemiluminescence is the correct choice: it detects light from the NO–O3 reaction, a unique hallmark of this NOx measurement approach. Other options don’t use this light-emission detection. Nondispersive infrared spectroscopy relies on infrared absorption by gases, not chemiluminescence. Pararosaniline refers to a colorimetric color-change method, which produces a visible color rather than light from a chemical reaction detected as photons. A transmissometer measures how much light passes through a sample to assess turbidity, not gas concentrations.

The technique that uses chemiluminescence detection for NOx relies on light produced during a chemical reaction. In this method, nitric oxide (NO) reacts with ozone (O3) to form an excited NO2 species (NO2*), which emits photons as it relaxes to its ground state. A photomultiplier or similar detector measures that light, and the signal is proportional to the NO concentration in the gas. To measure total NOx, the sample can first pass through a converter that converts NO2 to NO, so the detector’s signal represents all oxides of nitrogen as NO. This is why chemiluminescence is the correct choice: it detects light from the NO–O3 reaction, a unique hallmark of this NOx measurement approach.

Other options don’t use this light-emission detection. Nondispersive infrared spectroscopy relies on infrared absorption by gases, not chemiluminescence. Pararosaniline refers to a colorimetric color-change method, which produces a visible color rather than light from a chemical reaction detected as photons. A transmissometer measures how much light passes through a sample to assess turbidity, not gas concentrations.