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The SIR Model S-5012 Nitrogen Oxides Analyzer is designed to measure the amount of nitric oxide (NO), nitrogen dioxide (NO2) and total oxides of nitrogen (NOx) in a continuous, ambient air sample. The instrument reacts quickly to changes in NO NO2 and NOx concentrations in the sample, while providing a highly stabilized measurement capability for extended periods, without repeated adjustments.
The analyzer utilizes the photometric detection of chemiluminescence which results from the gas phase reaction of ozone with NO In this reaction, some of the resultant NO2 is produced in an electronically excited state; the excited NO2 immediately decays to the ground state (or normal NO2) while emitting light in the spectral region from about 600 nm to 2400 nm, with a peak at about 1200 nm. This phenomenon is known as chemiluminescence. The intensity of light generated in the reaction is proportional to the concentration of NO present, and the reaction is applicable to the direct measurement of atmospheric concentrations of NO.
tvleasurements of NO2 are made indirectly by first reducing the NO2 to NO her reacting the resultant NO with ozone and measuring the light intensity from the reaction. In practice, the NO2 in a sample of air is first reduced to NO by means of a converter. Any NO, which is already present in the at sample, passes through the converter unchanged, causing a resultant total NOx concentration equal to NO + NO2. A portion of the air sample is also reacted with ozone without having passed through the converter, which yields the NO concentration. This latter NO measurement is subtracted from the previous NOx measurement (NO + NO2) to yield the final NO2 measurement.
The analyser provides automatic cycling between the NO and NOx measurements, with the concentrations (NO2) updated and displayed after each cycle. Normal cycle time is approximately 24 seconds.
MODEL S-5012 Chemiluminescence NO-NO2-NOx Analyzer
