Ambient Air quality Monitoring Guidlines. - Maharashtra Pollution ...

9. CONTINUOUS MEASUREMENT OF OXIDES OF
NITROGEN IN AMBIENT AIR BY CHEMILUMINESCENCE
1.0 TITLE
Method for continuous measurement of oxides of nitrogen in ambient air by
chemiluminescence.
2.0 PURPOSE
The purpose is to lay down a uniform and reliable method for measurement of
oxides of nitrogen in ambient air.
3.0 PRINCIPLE
3.4 The measurement method is based upon the rapid chemiluminescent reaction of
nitric oxide (NO) with excess ozone (O3) (1, 2). The reaction is made to take
place in a light free chamber.
NO + O3 → NO*2 + O2
K = 1.0 x 10 7 L mol -1 sec -1
A portion of the resultant nitrogen dioxide is produced in a highly excited energy
state (NO*2) and subsequently decays to the ground level state emitting light in a
broad frequency band with a peak at about 1200 nm :
NO*2 → NO2 + photons (hv)
The intensity of the light emitted is linearly proportional to the nitric oxide
concentration and is measured by a photomultiplier tube.
3.5 Atmospheric nitric oxide is determined directly in a sample stream as described
in Section 3.1.
3.6 Atmospheric nitrogen dioxide in a sample stream is measured indirectly after
conversion to nitric oxide. (Converters capable of this reduction are described in
Section 8.1). The detection and determination of the total oxides of nitrogen (NO
+ NO from NO2) then proceeds as shown in Section 3.1. The NO2 concentration
is calculated by the subtraction of the measured NO concentration from the
measured total oxides of nitrogen.
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