Model 405 nm NO
2
/NO/NO
x
Monitor Manual Rev. D
27
7.2.2. Measurement of Zero Air
1. Verify that the zero air supply is on and the calibrator is set to output zero
air only.
2. Allow the Model 405 nm to sample zero air until the response is stable.
3. Record the average zero air responses.
7.2.3. Measurement of NO
2
and NO Standards
1. Allow the Model 405 nm to sample zero air until a stable response is
measured and record the average responses.
2. To equilibrate the system, generate an NO concentration significantly
higher than twice the concentration range of NO
2
that will be calibrated and
allow the calibrator and equipment to equilibrate for at least 10 minutes.
3. The NO concentration should not be changed for the rest of the calibration.
4. Allow the Model 405 nm to sample the NO concentration standard until a
stable response is measured and record the average responses.
5. Generate an ozone concentration at the high end of the concentration
range of NO
2
that will be calibrated and allow the calibrator and equipment
to equilibrate for at least 10 minutes.
6. Allow the Model 405 nm to sample the NO
2
and NO concentration
standards until a stable response is measured and record the average
responses.
7. Generate several other ozone concentrations to produce other
concentrations of NO
2
and NO. At least 4 concentration standards are
recommended over the range of interest.
8. For each concentration, record the responses of the Model 405 nm.
9. Turn off the ozone generator and continue to produce the NO
concentration used during the calibration process and allow the calibrator
and equipment to equilibrate for at least 10 minutes.
10. Verify that the standing NO concentration used during the calibration did
not change more than a few ppb from the beginning of the calibration
procedure. If the NO concentration is significantly different at the
beginning and end of the calibration, then the calibration setup was not
adequately equilibrated before collecting measurements.
11. Allow the Model 405 nm to sample zero air until a stable response is
measured and record the average responses.
7.2.4. Calibration Curve
1. Calculate the measured NO
2
as the difference between the average zero
response and the response at each concentration of NO
2
. Any offset from
background NO
2
released from the GPT chamber will be cancelled out this
way.
2. Calculate the measured NO as the difference between the average
standing NO concentration during the calibration and response at each
concentration of NO.
