Chemiluminescent method for continuous monitoring of nitrous acid in ambient air

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Abstract
A continuous-flow method for measuring atmospheric HNO2 concentration in real time has been developed that uses a chemiluminescent NOx monitor. A Na2CO3 solution strips gaseous HNO2 from the atmosphere by means of pulling an air sample and the solution through a glass coil and mixing continuously with ascorbic acid solution which reduces nitrite to NO. The mixture is led into a gas-liquid separating coil consisting of microporous PTFE tubing. The NO evolved from the separting coil is swept out by a stream of clean air and detected with a chemiluminescent NOx monitor. The technique utilizes a dual flow system and dual channel NOx monitor to correct positive interferences from NO2 and peroxyacetylnitrate (PAN). The concentration of HNO2 is determined by difference between the two measurements. Sensitivity of the method is a function of the ratio of sampling flow rate to carrier gas flow rate, which permits readily a highly sensitive measurement.

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