Simultaneous determination of atmospheric nitric acid and nitrous acid by reduction with hydrazine and ascorbic acid with chemiluminescence detection

A continuous-flow system for the simultaneous determination of atmospheric HNO3 and HNO2 has been developed that consists of two sets of dual-channel flow systems: one is for the measurement of total HNO3—HNO2 and the other is for the measurement of HNO2. Nitric acid and HNO2 are continuously stripped from the atmosphere into an NaOH solution by drawing the air sample and the solution through a glass coil. The nitrate is reduced with hydrazine sulfate in the presence of Cu11 to nitrite, which is then reduced to NO with ascorbic acid solution, and the NO is detected by a chemiluminescence NOx analyser. This measurement system can also be used to determine HNO2, thus giving the total concentration of HNO3 and HNO2. The measurement system without the hydrazine reduction procedure determines HNO2 alone. The concentration of HNO3 is determined by the difference between the two measurements. Of the common pollutants, NO2 and peroxyacetyl nitrate showed positive interferences. In order to correct for these positive interferences, each of the measurement systems utilizes a dual flow system and a dual-channel NOx analyser.