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

8. DETERMINATION OF NITROGEN DIOXIDE IN THE
ATMOSPHERE
1.0 TITLE
Method for determination of Nitrogen Dioxide in the Atmosphere (Sodium
Arsenite method).
2.0 PURPOSE
The purpose is to lay down an uniform and reliable method for sampling and
analysis of nitrogen dioxide in ambient air.
3.0 PRINCIPLE
3.1 Ambient nitrogen dioxide (NO2) is collected by bubbling air through a solution of
sodium hydroxide and sodium arsenite. The concentration of nitrite ion (NO - 2)
produced during sampling is determined colorimetrically by reacting the nitrite ion
with phosphoric acid, sulfanilamide, and N-(1-naphthyl)-ethylenediamine dihydrochloride
(NEDA) and measuring the absorbance of the highly colored azodye
at 540 nm.
3.2 The nominal range of the method is 9 to 750 µg NO2/m 3 (0.005 to 0.4 ppm) 3 .
The range of the analysis is 0.04 to 2.0 µg NO - 2/ml, following Beer's Law
throughout this range (0 to 1.0 absorbance units). Under the specified conditions
of 50 ml of absorbing reagent, a sampling rate of 200 cm 3 /min for 24 hours, and
a sampling efficiency of 0.82, the range of the method is, therefore, 9 to 420
µg/NO2/m 3 (0.005 to 0.22 ppm). Nitrogen dioxide concentrations in the range of
420 to 750 µg/m 3 (0.22 to 0.4 ppm) are accurately measured by 1:1 dilution of
the collected sample.
3.3 Based on results from a collaborative study, the within laboratory standard
deviation is 8 µg/m 3 (0.004 ppm) and the between laboratory standard deviation
is 11 µg/m 3 (0.006 ppm) over the range of 50 to 300 µg NO2/m 3 (0.027 to 1.16
ppm) 4 .
3.4 Based on results from a collaborative study, the method has an average bias of -
3% over the range of 50 to 300 µg NO2/m 3 (0.027 to 0.16 ppm) 4 .
4.0 SCOPE
This method is applicable to 24 hours integrated sampling of NO2 in ambient air.
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