Ambient NOx Monitor

The APNA-370 uses a combination of the dual cross flow modulation type chemiluminescence principle and the referential calculation method.
This gives it the advantages of the single-detector method plus the ability to do continuous measurements of NOx, NO, and NO₂. The design gives great stability and extremely high sensitivity (0.1 ppm F.S.)

Standard equipment includes a drier unit with an automatic recycle function to provide dry ambient air as the ozone source. This makes long-term continuous measurements possible.

The detector uses a silicon photodiode sensor to reduce size and prolong working life.

All the necessary features are built right into a single rack-sized unit, including a reference-gas generator, an ozone-source drier unit, an ozone decomposer, and a sampling pump. No supplemental gas is required.

Cross flow modulation type, reduced pressure chemiluminescence (CLD)
The chemiluminescence method uses the reaction of NO with O₃
NO+O₃ → NO₂*+O₂
NO₂+NO₂+h ν
A portion of the NO₂ generated as the result of this reaction becomes NO₂*. As these excited molecules return to the ground state, chemiluminescence is generated in the range of 600 nm to 3,000 nm. The light intensity is in proportion to the concentration of NO molecules and by measuring it we obtain the NO concentration of the sample. A deoxidation conver-ter changes the NO₂ to NO, which is measured. In other words, the NO₂ concentration can be obtained by the difference between (1) the NOx concentration measured when the sample gas is directed through a converter and (2) the NO concentration measured when the gas is not run through the converter.