Measuring of nitrous Acid in the City of Gothenburg

Atmospheric concentrations of nitrous acid were measured during a five months period in central Gothenburg. Samples of HNO2 were collected in 12-hrs intervals by means of an ompregnated denuder technique. The sampling was followed by colorimetric analysis with respect to nitrite ions. During the period January ot May values in the range of approximately 1 to 50 nmole/m3 were observed. Simultaneous mesurement of NO, NO2 and H2O show that observed nighttime HNO2 is approximately 10-50 % of calculated equilibrium concentrations, while the daytime fraction is markedly lower. This indicates that HNO2 is decomposed to OH-radicale during daytime by daylight pholotysis. Correlation coefficient calculations for ambient HNO2 and NO-, NO2-N + NO2 + H2O to 2HNO2 is the major sources of nitrous acid at night.