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

10. DETERMINATION OF OZONE IN THE ATMOSPHERE
1.0 TITLE
Method for determination of Ozone in the Atmosphere (Chemical Method).
2.0 PURPOSE
The purpose is to lay down an uniform and reliable method for sampling and
analysis of ozone in ambient air.
3.0 PRINCIPLE
3.1 Micro-amounts of ozone and the oxidants liberate iodine when absorbed in a 1%
solution of potassium iodine buffered at pH 6.8 + 0.2. The iodine is determined
spectrophotometrically by measuring the absorption of triiodide ion at 352 nm.
3.2 The stoichiometry is approximated by the following reaction :
O3 + 3 KI + H2O --> KI3 + 2 KOH + O2
3.3 This method covers the manual determination of oxidant concentrations between
0.01 to 10 ppm (19.6 to 19620 µg/m 3 ) as ozone (1).
3.4 When 10 ml of absorbing solution is used, between 1 and 10 µl of ozone,
corresponding to absorbance between 0.1 and 1 in a 1 cm cell, are collected.
3.5 The precision of the method within the recommended range (Section 3.2) is
about + 5% deviation from the mean. The major error is from loss of iodine
during sampling periods; this can be reduced by using a second impinger.
3.6 The accuracy of this method has not been established for atmospheric sampling.
3.7 The method was compared against an absolute ultraviolet photometer (8). In the
range of 40-60% relative humidity (see section 7.6) the ozone-iodine
stoichiometry was 1.25 and not 1.00 as suggested by the equation in Section 3.2.
4.0 SCOPE
This method is applicable for measurement of ozone present in ambient air.
5.0 INTERFERENCES
5.1 Sulfur dioxide produces a negative interference equivalent to 100% of that of an
equimolar concentration of oxidant.
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