Chemiluminescent method for continuous monitoring of nitrous acid in ambient air

A continuous-flow method for measuring atmospheric HNO{sub 2} concentration in real time has been developed that uses a chemiluminescent NO{sub x} monitor. A Na{sub 2}CO{sub 3} solution strips gaseous HNO{sub 2} 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 separating coil is swept out by a stream of clean air and detected with a chemiluminescent NO{sub x} monitor. The technique utilizes a dual flow system and dual channel NO{sub x} monitor to correct positive interferences from NO{sub 2} and peroxyacetylnitrate (PAN). The concentration of HNO{sub 2} 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.