CHEMILUMINESCENCE
LIGHT-BASED MEASUREMENTS FOR NOx ANALYSIS
Chemiluminescence detectors take advantage of nitric oxide ( NO ) and nitrogen dioxide ( NO 2 ) chemical reactions that emit light as part of that process . This is different from fluorescence or phosphorescence , in that the light produced stems from a chemical reaction rather than by the absorption of photons by the molecule .
Chemiluminescence analyzers use a thermally stabilized photodiode to measure the intensity of the light produced by the reaction of NO with ozone ( O 3 ). The intensity is directly proportional to the concentration of NO that was converted to NO 2 by the reaction .
By converting the NO 2 in the gas stream to NO , then reacting it with the O 3 , the total NOx value can be calculated , allowing speciation of NO , NO 2 and total NOx with a single analyzer .
CHEMILUMINESCENCE PROCESS DIAGRAM
AMBIENT AIR
NO + NO 2
NO 2 to NO catalyst
NO
SWITCHING VALVE
WINDOW
REACTION CHAMBER
O 3 + NO |
NO 2 * + O 2
|
NO 2 * |
NO 2 + light |
MULTIPLIER PHOTOTUBE
ELECTRONIC SIGNAL PROCESSOR
O 3
OZONIZER VACUUM PUMP
O 2
OXYGEN SOURCE VENT
P70