Abstract

The effect of the two most critical parameters, the sample flow rate and sampling duration, on the absorption efficiency of NO₂ in the sodium arsenite method of nitrogen dioxide determination in ambient air was studied. Laboratory experiments showed a high sensitivity to these parameters, which were subjected to variation during actual field monitoring. The reported NO₂ absorption efficiency of the method of 82% at a flow rate of 0.2 l min⁻¹ was found to be as low as 33% at a flow rate of 1.0 l min⁻¹ for a sampling duration of 24 h. Similarly, a considerable decrease in absorption efficiency with increasing sampling duration from 2 to 24 h was observed at a particular flow rate. Correction factors for the absorption efficiency were evolved that can be used to update the existing database, as well as future NO₂ data generated using this manual monitoring method.