Instrument - Nitrogen oxide analyzer

Short name:
NOx monitor

Full name:
Nitrogen oxide analyzer

What is being measured:

Sampling Protocol:



Instrument year :
None specified

Data recording software:

Data analysis software:

Raw data time resolution:
0.1 Hz

Analysis data averaging:

Detection limit:
0.4 ppb

Sensitivity to temperature (and correction method, if applicable): :
Since the density of the sample gas effects the brightness of the chemiluminescence reaction, the M200E software compensates for temperature and pressure changes. Stability is further enhanced by an Auto-Zero feature which periodically redirects the gas flow through the analyzer so that no chemiluminescence reaction is present in the sample chamber. The analyzer measures this "dark" condition and uses the results as an offset, which is subtracted from the sensor readings recorded while the instrument is measuring NO and NOx.

Sensitivity to relative humidity (and correction method, if applicable): :

Sampling method:
Direct sampling

Sample preparation method:

Sample residence time (chamber to instrument) (seconds):

Length of tubing (cm):

Instrument flow rate:

Tubing inner diameter:

Tubing material:
FEP Teflon

Chemical identification method:
The instrument calculates the amount of NO present by measuring the amount of chemiluminescence given off when the sample gas is exposed to ozone (O3). A catalytic-reactive converter converts any NO2 in the sample gas to NO, which is then measured as above (including the original NO in the sample gas) and reported as NOx. NO2 is calculated as the difference between NOx and NO.

Data analysis method:
The data is saved to Excel as a timeseries of NO, NO2 and NOx concentrations. It is post-averaged if required and then timeseries are plotted. If "instrument background" measurements were taken, they are subtracted from the timeseries.

Quantification method:

Calibration method:
A multipoint calibration is done where a span gas of NO+clean air at different mixing ratios is fed into the instrument. The span gas injection takes place over an hour for each calibration point, to ensure appropriately clean lines and therefore correct measurements. A plot of actual injected concentration versus the instrument measured concentration is made.

Calibration drift estimate:
Low (on the order of weeks)

Calibration schedule:
As Needed

Uncertainty estimation method:
Triplicate measurements are taken for each calibration point and the average uncertainty is calculated based on the % difference between the instrument readings.

Known interferences:
Common interferences for this NOx monitor includes NH3, which can also be converted to NO2 in the reaction cell and can therefore artificially increase the estimated NOx concentration. Carbon dioxide, excess water vapor, and sulfur dioxide gas could also produce measurement artifacts. Gas-phase organic nitrates such as isopropyl nitrate, as well as HNO3 can also inflate the NOx measurements.

Link to supplemental information:

Additional notes:

Measurement uncertainty:

Measurement units: