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

Abstract

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 NO_x 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 NO_x analyser.