A simple Method for Determination of gaseous nitrous Acid in the Atmosphere

A denuder technique for sampling an analysing nitrous acid at sub ppb level is described. After sampling teh denuder is leached in waer and the NO2-concentration is determined spectrophotometrically. The detection limit for 24 hours sampling is better than 0.02 ppb. PAN might be an important interference in background air during summertime conditions. The method was tested on synthetic gas mixtures of NO, NO2 and HNO2. It has been appeared that HNO2 can be formed by heterogeneous rections at surfaces. Measurements in the city of Gothenburg indicate that the major pathwy for HNO2-formation in urban air is the reaction between NO, NO2 and water vapor.