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

6. CONTINUOUS MEASUREMENT OF SULPHUR DIOXIDE -
ULTRAVIOLET FLUORESCENCE METHOD
1.0 TITLE
Method for continuous measurement of Sulphur Dioxide - Ultravoilet
Fluorescence method.
2.0 PURPOSE
The purpose is to lay down a uniform and reliable method for measurement of
sulphur dioxide in ambient air.
3.0 PRINCIPLE
The UV fluorescence method is based on the fluorescence emission of light by
SO2 molecules previously excited by UV radiation.
The first reaction step is :
SO2 + hυ 1 (UV) → SO2 *
Then in the second step, the excited SO2 * molecule returns to the original ground
state, emitting an energy hυ 1 according to the reaction :
SO2 * → SO2 + hυ 1 (UV)
The intensity of the fluorescent radiation is proportional to the number of SO2
molecules in the detection volume and is therefore proportional to the
concentration of SO2.
Therefore :
F = k [SO2]
where :
F = is the intensity of fluorescence radiation;
k = is the factor of proportionality;
[SO2] = concentration of SO2
The air sample flows into the inlet of the analyser where it is scrubbed to remove
any interference by aromatic hydrocarbons that may be present. A hydrocarbon
scrubber device usually accomplishes this.
100