Nitrogen Oxides (NO/NO2/NOX)
About Nitrogen Oxides
The nitric oxide (NO) molecule is quite reactive and unstable. In ambient air, it reacts with oxygen to form the toxic nitrogen dioxide (NO2).
Human activity has drastically increased the production of nitric oxide in combustion chambers, e.g. car engines and power plants.
The phase in of the new NO2 thresholds values will make the nitrogen oxides a subject of major public interest.
Health and Environmental Effects
Nitric oxide has a multitude of effects, primarily in the lung but also in other organs, such as the spleen and the liver. In the blood it leads to the creation of metahemoglobin, which cannot transport oxygen. Nitric oxide in the air may later convert to nitric acid in acid rain. Furthermore, both NO and NO2 participate in the ozone layer reduction.
Sources: WHO Regional Publications, European Series, No. 91, "Air quality guidelines for Europe", 2nd edition, 2000;
GESTIS Stoffdatenbank (http://www.hvbg.de/d/bia/fac/stoffdb/index.html); U.S. Environmental Protection Agency (www.epa.gov)
Nitrogen Oxides and the airpointer®
Measuring Principle: Chemiluminescence (EN 14211)
NO / NO2 / NOX / Chemiluminescence
Nitric Oxides in the sample gas react with ozone and this reaction results in electrically excited molecules. The molecules release their excess energy by emitting photons, which are measured by a photomultiplier tube. The airpointer® NOX Module is equipped with a delay loop to allow NO and NO2 results from the identical sample.
A zero air source is included in every airpointer®, so a zero point check can be performed periodically e.g. once a day. An internal NO2 source is optionally available for a periodical span point check.
|Component||Nitrogen Oxides NO/NO2/NOX
|EU Directive / EPA Methodology||Chemiluminescence (EN 14211)
|Range||Dynamic, up to 20 ppm
|Zero Noise||0.2 ppb RMS
|Lower Detectable Limit||0.4 ppb
|Zero Drift (24 Hour)||< 0.4 ppb|
|Span Drift (24 Hour)
||+/- 1% of reading > 100 ppb
|Response Time||< 60 seconds|
|Precision||1% of reading or 1 ppb (whichever is greater) @ < 500 ppb
|Linearity||+/- 1% of reading > 100 ppm|
|Sample Flow Rate||1000 ml/min|